Tejun Heo [Fri, 22 May 2015 22:23:34 +0000 (18:23 -0400)]
writeback: reset wb_domain->dirty_limit[_tstmp] when memcg domain size changes
The amount of available memory to a memcg wb_domain can change as
memcg configuration changes. A domain's ->dirty_limit exists to
smooth out sudden drops in dirty threshold; however, when a domain's
size actually drops significantly, it hinders the dirty throttling
from adjusting to the new configuration leading to unexpected
behaviors including unnecessary OOM kills.
This patch resolves the issue by adding wb_domain_size_changed() which
resets ->dirty_limit[_tstmp] and making memcg call it on configuration
changes.
Tejun Heo [Fri, 22 May 2015 22:23:33 +0000 (18:23 -0400)]
writeback: implement memcg wb_domain
Dirtyable memory is distributed to a wb (bdi_writeback) according to
the relative bandwidth the wb is writing out in the whole system.
This distribution is global - each wb is measured against all other
wb's and gets the proportinately sized portion of the memory in the
whole system.
For cgroup writeback, the amount of dirtyable memory is scoped by
memcg and thus each wb would need to be measured and controlled in its
memcg. IOW, a wb will belong to two writeback domains - the global
and memcg domains.
The previous patches laid the groundwork to support the two wb_domains
and this patch implements memcg wb_domain. memcg->cgwb_domain is
initialized on css online and destroyed on css release,
wb->memcg_completions is added, and __wb_writeout_inc() is updated to
increment completions against both global and memcg wb_domains.
The following patches will update balance_dirty_pages() and its
subroutines to actually consider memcg wb_domain for throttling.
Tejun Heo [Fri, 22 May 2015 22:23:32 +0000 (18:23 -0400)]
writeback: update wb_over_bg_thresh() to use wb_domain aware operations
wb_over_bg_thresh() currently uses global_dirty_limits() and
wb_dirty_limit() both of which are wrappers around operations which
take dirty_throttle_control. For cgroup writeback support, the
function will be updated to also consider memcg wb_domains which
requires the context information carried in dirty_throttle_control.
This patch updates wb_over_bg_thresh() so that it uses the underlying
wb_domain aware operations directly and builds the global
dirty_throttle_control in the process.
This patch doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:31 +0000 (18:23 -0400)]
writeback: move over_bground_thresh() to mm/page-writeback.c
and rename it to wb_over_bg_thresh(). The function is closely tied to
the dirty throttling mechanism implemented in page-writeback.c. This
relocation will allow future updates necessary for cgroup writeback
support.
While at it, add function comment.
This is pure reorganization and doesn't introduce any behavioral
changes.
Tejun Heo [Fri, 22 May 2015 22:23:30 +0000 (18:23 -0400)]
writeback: separate out domain_dirty_limits()
global_dirty_limits() calculates thresh and bg_thresh (confusingly
called *pdirty and *pbackground in the function) assuming
global_wb_domain; however, cgroup writeback support requires
considering per-memcg wb_domain too.
This patch separates out domain_dirty_limits() which takes
dirty_throttle_control out of global_dirty_limits(). As thresh and
bg_thresh calculation needs the amount of dirtyable memory in the
domain, dirty_throttle_control->avail is added. The new function
calculates the two thresholds and store them directly in the
dirty_throttle_control.
Also, as memcg domains can't follow vm_dirty_bytes and
dirty_background_bytes settings directly. If those are set and
domain_dirty_limits() is invoked for a !global domain, the settings
are translated to ratios by scaling them against globally available
memory. dirty_throttle_control->gdtc is added to enable this when
CONFIG_CGROUP_WRITEBACK.
global_dirty_limits() is now a thin wrapper around
domain_dirty_limits() and balance_dirty_pages() is updated to use the
new function too.
This patch doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:29 +0000 (18:23 -0400)]
writeback: make __wb_writeout_inc() and hard_dirty_limit() take wb_domaas a parameter
Currently __wb_writeout_inc() and hard_dirty_limit() assume
global_wb_domain; however, cgroup writeback support requires
considering per-memcg wb_domain too.
This patch separates out domain-specific part of __wb_writeout_inc()
into wb_domain_writeout_inc() which takes wb_domain as a parameter and
adds the parameter to hard_dirty_limit(). This will allow these two
functions to handle per-memcg wb_domains.
This patch doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:28 +0000 (18:23 -0400)]
writeback: add dirty_throttle_control->dom
Currently all dirty throttle operations use global_wb_domain; however,
cgroup writeback support requires considering per-memcg wb_domain too.
This patch adds dirty_throttle_control->dom and updates functions
which are directly using globabl_wb_domain to use it instead.
As this makes global_update_bandwidth() a misnomer, the function is
renamed to domain_update_bandwidth().
This patch doesn't introduce any behavioral changes.
wb->completions measures the wb's proportional write bandwidth in
global_wb_domain and thus naturally tied to the wb_domain. This patch
adds dirty_throttle_control->wb_completions which is initialized to
wb->completions by GDTC_INIT() and updates __wb_dirty_limits() to use
it instead of dereferencing wb->completions directly.
This will allow dirty_throttle_control to represent different
wb_domains and the matching wb completions.
This patch doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:26 +0000 (18:23 -0400)]
writeback: add dirty_throttle_control->pos_ratio
wb_position_ratio() is used to calculate pos_ratio, which is used for
two purposes. wb_update_dirty_ratelimit() uses it to adjust
wb->[balanced_]dirty_ratelimit gradually and balance_dirty_pages() to
immediately adjust dirty_ratelimit right before applying it to
determine pause duration.
While wb_update_dirty_ratelimit() is separately rate limited from
balance_dirty_pages(), on the run where the ratelimit is updated, we
end up calculating pos_ratio twice with the same parameters.
This patch adds dirty_throttle_control->pos_ratio.
balance_dirty_pages() calculates it once per run and
wb_update_dirty_ratelimit() uses the value stored in
dirty_throttle_control.
This removes the duplicate calculation and also will help implementing
memcg wb_domain.
Tejun Heo [Fri, 22 May 2015 22:23:25 +0000 (18:23 -0400)]
writeback: make __wb_calc_thresh() take dirty_throttle_control
wb_calc_thresh() calculates wb_thresh by scaling thresh according to
the wb's portion in the system-wide write bandwidth. cgroup writeback
support would need to calculate wb_thresh against memcg domain too.
This patch renames wb_calc_thresh() to __wb_calc_thresh() and makes it
take dirty_throttle_control so that the function can later be updated
to calculate against different domains according to
dirty_throttle_control.
wb_calc_thresh() is now a thin wrapper around __wb_calc_thresh().
v2: The original version was incorrectly scaling dtc->dirty instead of
dtc->thresh. This was due to the extremely confusing function and
variable names. Added a rename patch and fixed this one.
wb_bg_thresh is currently treated as a second-class citizen. It's
only used when BDI_CAP_STRICTLIMIT is set and balance_dirty_pages()
doesn't calculate it unless the cap is set. When the cap is set, the
calculated value is not passed around but instead recalculated
whenever it's used.
wb_position_ratio() calculates it by scaling wb_thresh proportional to
bg_thresh / thresh. wb_update_dirty_ratelimit() uses wb_dirty_limit()
on bg_thresh, which should generally lead to a similar result as the
proportional scaling but can also be way off in the presence of
max/min_ratio settings.
Avoiding wb_bg_thresh calculation saves us one u64 multiplication and
divsion when BDI_CAP_STRICTLIMIT is not set. Given that
balance_dirty_pages() is already ratelimited, this doesn't justify the
incurred extra complexity.
This patch adds wb_bg_thresh to dirty_throttle_control and makes
wb_dirty_limits() always calculate it and updates the users to use the
pre-calculated value.
Tejun Heo [Fri, 22 May 2015 22:23:23 +0000 (18:23 -0400)]
writeback: consolidate dirty throttle parameters into dirty_throttle_control
Dirty throttling implemented in balance_dirty_pages() and its
subroutines makes use of a number of parameters which are passed
around individually. This renders these functions somewhat unwieldy
and makes it difficult to add or change the involved parameters. Also
some functions use different or conflicting naming schemes for the
same parameters making the code confusing to follow.
This patch consolidates the main parameters into struct
dirty_throttle_control so that they can be passed around easily and
adding new paramters isn't painful. This also unifies how a given
parameter is named and accessed. The drawback of using this type of
control structure rather than explicit paramters is that it isn't
immediately obvious which function accesses and modifies what;
however, it's fairly clear that the benefits outweigh in this case.
GDTC_INIT() macro is provided to ease initializing
dirty_throttle_control for the global_wb_domain and
balance_dirty_pages() uses a separate pointer to point to its global
dirty_throttle_control. This is to make it uniform with memcg domain
handling which will be added later.
This patch doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:22 +0000 (18:23 -0400)]
writeback: move global_dirty_limit into wb_domain
This patch is a part of the series to define wb_domain which
represents a domain that wb's (bdi_writeback's) belong to and are
measured against each other in. This will enable IO backpressure
propagation for cgroup writeback.
global_dirty_limit exists to regulate the global dirty threshold which
is a property of the wb_domain. This patch moves hard_dirty_limit,
dirty_lock, and update_time into wb_domain.
This is pure reorganization and doesn't introduce any behavioral
changes.
Tejun Heo [Fri, 22 May 2015 22:23:21 +0000 (18:23 -0400)]
writeback: implement wb_domain
Dirtyable memory is distributed to a wb (bdi_writeback) according to
the relative bandwidth the wb is writing out in the whole system.
This distribution is global - each wb is measured against all other
wb's and gets the proportinately sized portion of the memory in the
whole system.
For cgroup writeback, the amount of dirtyable memory is scoped by
memcg and thus each wb would need to be measured and controlled in its
memcg. IOW, a wb will belong to two writeback domains - the global
and memcg domains.
Currently, what constitutes the global writeback domain are scattered
across a number of global states. This patch starts collecting them
into struct wb_domain.
* fprop_global which serves as the basis for proportional bandwidth
measurement and its period timer are moved into struct wb_domain.
* global_wb_domain hosts the states for the global domain.
* While at it, flatten wb_writeout_fraction() into its callers. This
thin wrapper doesn't provide any actual benefits while getting in
the way.
This is pure reorganization and doesn't introduce any behavioral
changes.
Tejun Heo [Fri, 22 May 2015 22:23:20 +0000 (18:23 -0400)]
writeback: reorganize [__]wb_update_bandwidth()
__wb_update_bandwidth() is called from two places -
fs/fs-writeback.c::balance_dirty_pages() and
mm/page-writeback.c::wb_writeback(). The latter updates only the
write bandwidth while the former also deals with the dirty ratelimit.
The two callsites are distinguished by whether @thresh parameter is
zero or not, which is cryptic. In addition, the two files define
their own different versions of wb_update_bandwidth() on top of
__wb_update_bandwidth(), which is confusing to say the least. This
patch cleans up [__]wb_update_bandwidth() in the following ways.
* __wb_update_bandwidth() now takes explicit @update_ratelimit
parameter to gate dirty ratelimit handling.
* mm/page-writeback.c::wb_update_bandwidth() is flattened into its
caller - balance_dirty_pages().
* fs/fs-writeback.c::wb_update_bandwidth() is moved to
mm/page-writeback.c and __wb_update_bandwidth() is made static.
* While at it, add a lockdep assertion to __wb_update_bandwidth().
Except for the lockdep addition, this is pure reorganization and
doesn't introduce any behavioral changes.
Tejun Heo [Fri, 22 May 2015 22:23:19 +0000 (18:23 -0400)]
writeback: clean up wb_dirty_limit()
The function name wb_dirty_limit(), its argument @dirty and the local
variable @wb_dirty are mortally confusing given that the function
calculates per-wb threshold value not dirty pages, especially given
that @dirty and @wb_dirty are used elsewhere for dirty pages.
Let's rename the function to wb_calc_thresh() and wb_dirty to
wb_thresh.
Tejun Heo [Fri, 22 May 2015 22:23:18 +0000 (18:23 -0400)]
memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online
cpu_possible_mask represents the CPUs which are actually possible
during that boot instance. For systems which don't support CPU
hotplug, this will match cpu_online_mask exactly in most cases. Even
for systems which support CPU hotplug, the number of possible CPU
slots is highly unlikely to diverge greatly from the number of online
CPUs. The only cases where the difference between possible and online
caused problems were when the boot code failed to initialize the
possible mask and left it fully set at NR_CPUS - 1.
As such, most per-cpu constructs allocate for all possible CPUs and
often iterate over the possibles, which also has the benefit of
avoiding the blocking CPU hotplug synchronization.
memcg open codes per-cpu stat counting for mem_cgroup_read_stat() and
mem_cgroup_read_events(), which iterates over online CPUs and handles
CPU hotplug operations explicitly. This complexity doesn't actually
buy anything. Switch to iterating over the possibles and drop the
explicit CPU hotplug handling.
Eventually, we want to convert memcg to use percpu_counter instead of
its own custom implementation which also benefits from quick access
w/o summing for cases where larger error margin is acceptable.
This will allow mem_cgroup_read_stat() to be called from non-sleepable
contexts which will be used by cgroup writeback.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Michal Hocko <mhocko@suse.cz> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:14:05 +0000 (17:14 -0400)]
ext2: enable cgroup writeback support
Writeback now supports cgroup writeback and the generic writeback,
buffer, libfs, and mpage helpers that ext2 uses are all updated to
work with cgroup writeback.
This patch enables cgroup writeback for ext2 by adding
FS_CGROUP_WRITEBACK to its ->fs_flags.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: linux-ext4@vger.kernel.org Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:14:04 +0000 (17:14 -0400)]
mpage: make __mpage_writepage() honor cgroup writeback
__mpage_writepage() is used to implement mpage_writepages() which in
turn is used for ->writepages() of various filesystems. All writeback
logic is now updated to handle cgroup writeback and the block cgroup
to issue IOs for is encoded in writeback_control and can be retrieved
from the inode; however, __mpage_writepage() currently ignores the
blkcg indicated by the inode and issues all bio's without explicit
blkcg association.
This patch updates __mpage_writepage() so that the issued bio's are
associated with inode_to_writeback_blkcg_css(inode).
v2: Updated for per-inode wb association.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Tue, 2 Jun 2015 14:37:23 +0000 (08:37 -0600)]
buffer, writeback: make __block_write_full_page() honor cgroup writeback
[__]block_write_full_page() is used to implement ->writepage in
various filesystems. All writeback logic is now updated to handle
cgroup writeback and the block cgroup to issue IOs for is encoded in
writeback_control and can be retrieved from the inode; however,
[__]block_write_full_page() currently ignores the blkcg indicated by
inode and issues all bio's without explicit blkcg association.
This patch adds submit_bh_blkcg() which associates the bio with the
specified blkio cgroup before issuing and uses it in
__block_write_full_page() so that the issued bio's are associated with
inode_to_wb_blkcg_css(inode).
v2: Updated for per-inode wb association.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:14:02 +0000 (17:14 -0400)]
writeback: dirty inodes against their matching cgroup bdi_writeback's
__mark_inode_dirty() always dirtied the inode against the root wb
(bdi_writeback). The previous patches added all the infrastructure
necessary to attribute an inode against the wb of the dirtying cgroup.
This patch updates __mark_inode_dirty() so that it uses the wb
associated with the inode instead of unconditionally using the root
one.
Currently, none of the filesystems has FS_CGROUP_WRITEBACK and all
pages will keep being dirtied against the root wb.
v2: Updated for per-inode wb association.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:14:01 +0000 (17:14 -0400)]
writeback: make writeback initiation functions handle multiple bdi_writeback's
[try_]writeback_inodes_sb[_nr]() and sync_inodes_sb() currently only
handle dirty inodes on the root wb (bdi_writeback) of the target bdi.
This patch implements bdi_split_work_to_wbs() and use it to make these
functions handle multiple wb's.
bdi_split_work_to_wbs() takes a base wb_writeback_work and create
clones of it and issue them to the wb's of the target bdi. The base
work's nr_pages is distributed using wb_split_bdi_pages() -
ie. according to each wb's write bandwidth's proportion in the bdi.
Cloning a bdi involves memory allocation which may fail. In such
cases, bdi_split_work_to_wbs() issues the base work directly and waits
for its completion before proceeding to the next wb to guarantee
forward progress and correctness under memory pressure.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
try_writeback_inodes_sb_nr() wraps writeback_inodes_sb_nr() so that it
handles s_umount locking and skips if writeback is already in
progress. The in progress test is performed on the root wb
(bdi_writeback) which isn't sufficient for cgroup writeback support.
The test must be done per-wb.
To prepare for the change, this patch factors out
__writeback_inodes_sb_nr() from writeback_inodes_sb_nr() and adds
@skip_if_busy and moves the in progress test right before queueing the
wb_writeback_work. try_writeback_inodes_sb_nr() now just grabs
s_umount and invokes __writeback_inodes_sb_nr() with asserted
@skip_if_busy. This way, later addition of multiple wb handling can
skip only the wb's which already have writeback in progress.
This swaps the order between in progress test and s_umount test which
can flip the return value when writeback is in progress and s_umount
is being held by someone else but this shouldn't cause any meaningful
difference. It's a fringe condition and the return value is an
unsynchronized hint anyway.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:59 +0000 (17:13 -0400)]
writeback: implement wb_wait_for_single_work()
For cgroup writeback, multiple wb_writeback_work items may need to be
issuedto accomplish a single task. The previous patch updated the
waiting mechanism such that wb_wait_for_completion() can wait for
multiple work items.
Issuing mulitple work items involves memory allocation which may fail.
As most writeback operations can't fail or blocked on memory
allocation, in such cases, we'll fall back to sequential issuing of an
on-stack work item, which would need to be waited upon sequentially.
This patch implements wb_wait_for_single_work() which waits for a
single work item independently from wb_completion waiting so that such
fallback mechanism can be used without getting tangled with the usual
issuing / completion operation.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:58 +0000 (17:13 -0400)]
writeback: implement bdi_wait_for_completion()
If the completion of a wb_writeback_work can be waited upon by setting
its ->done to a struct completion and waiting on it; however, for
cgroup writeback support, it's necessary to issue multiple work items
to multiple bdi_writebacks and wait for the completion of all.
This patch implements wb_completion which can wait for multiple work
items and replaces the struct completion with it. It can be defined
using DEFINE_WB_COMPLETION_ONSTACK(), used for multiple work items and
waited for by wb_wait_for_completion().
Nobody currently issues multiple work items and this patch doesn't
introduce any behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:57 +0000 (17:13 -0400)]
writeback: add wb_writeback_work->auto_free
Currently, a wb_writeback_work is freed automatically on completion if
it doesn't have ->done set. Add wb_writeback_work->auto_free to make
the switch explicit. This will help cgroup writeback support where
waiting for completion and whether to free automatically don't
necessarily move together.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:56 +0000 (17:13 -0400)]
writeback: make wakeup_dirtytime_writeback() handle multiple bdi_writeback's
wakeup_dirtytime_writeback() currently only starts writeback on the
root wb (bdi_writeback). For cgroup writeback support, update the
function to check all wbs.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:55 +0000 (17:13 -0400)]
writeback: make wakeup_flusher_threads() handle multiple bdi_writeback's
wakeup_flusher_threads() currently only starts writeback on the root
wb (bdi_writeback). For cgroup writeback support, update the function
to wake up all wbs and distribute the number of pages to write
according to the proportion of each wb's write bandwidth, which is
implemented in wb_split_bdi_pages().
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:54 +0000 (17:13 -0400)]
writeback: make bdi_start_background_writeback() take bdi_writeback instead of backing_dev_info
bdi_start_background_writeback() currently takes @bdi and kicks the
root wb (bdi_writeback). In preparation for cgroup writeback support,
make it take wb instead.
This patch doesn't make any functional difference.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:53 +0000 (17:13 -0400)]
writeback: make writeback_in_progress() take bdi_writeback instead of backing_dev_info
writeback_in_progress() currently takes @bdi and returns whether
writeback is in progress on its root wb (bdi_writeback). In
preparation for cgroup writeback support, make it take wb instead.
While at it, make it an inline function.
This patch doesn't make any functional difference.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:52 +0000 (17:13 -0400)]
writeback: make laptop_mode_timer_fn() handle multiple bdi_writeback's
For cgroup writeback support, all bdi-wide operations should be
distributed to all its wb's (bdi_writeback's).
This patch updates laptop_mode_timer_fn() so that it invokes
wb_start_writeback() on all wb's rather than just the root one. As
the intent is writing out all dirty data, there's no reason to split
the number of pages to write.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:51 +0000 (17:13 -0400)]
writeback: remove bdi_start_writeback()
bdi_start_writeback() is a thin wrapper on top of
__wb_start_writeback() which is used only by laptop_mode_timer_fn().
This patches removes bdi_start_writeback(), renames
__wb_start_writeback() to wb_start_writeback() and makes
laptop_mode_timer_fn() use it instead.
This doesn't cause any functional difference and will ease making
laptop_mode_timer_fn() cgroup writeback aware.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:49 +0000 (17:13 -0400)]
writeback: make bdi->min/max_ratio handling cgroup writeback aware
bdi->min/max_ratio are user-configurable per-bdi knobs which regulate
dirty limit of each bdi. For cgroup writeback, they need to be
further distributed across wb's (bdi_writeback's) belonging to the
configured bdi.
This patch introduces wb_min_max_ratio() which distributes
bdi->min/max_ratio according to a wb's proportion in the total active
bandwidth of its bdi.
v2: Update wb_min_max_ratio() to fix a bug where both min and max were
assigned the min value and avoid calculations when possible.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:48 +0000 (17:13 -0400)]
writeback: don't issue wb_writeback_work if clean
There are several places in fs/fs-writeback.c which queues
wb_writeback_work without checking whether the target wb
(bdi_writeback) has dirty inodes or not. The only thing
wb_writeback_work does is writing back the dirty inodes for the target
wb and queueing a work item for a clean wb is essentially noop. There
are some side effects such as bandwidth stats being updated and
triggering tracepoints but these don't affect the operation in any
meaningful way.
This patch makes all writeback_inodes_sb_nr() and sync_inodes_sb()
skip wb_queue_work() if the target bdi is clean. Also, it moves
dirtiness check from wakeup_flusher_threads() to
__wb_start_writeback() so that all its callers benefit from the check.
While the overhead incurred by scheduling a noop work isn't currently
significant, the overhead may be higher with cgroup writeback support
as we may end up issuing noop work items to a lot of clean wb's.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:47 +0000 (17:13 -0400)]
writeback: make bdi_has_dirty_io() take multiple bdi_writeback's into account
bdi_has_dirty_io() used to only reflect whether the root wb
(bdi_writeback) has dirty inodes. For cgroup writeback support, it
needs to take all active wb's into account. If any wb on the bdi has
dirty inodes, bdi_has_dirty_io() should return true.
To achieve that, as inode_wb_list_{move|del}_locked() now keep track
of the dirty state transition of each wb, the number of dirty wbs can
be counted in the bdi; however, bdi is already aggregating
wb->avg_write_bandwidth which can easily be guaranteed to be > 0 when
there are any dirty inodes by ensuring wb->avg_write_bandwidth can't
dip below 1. bdi_has_dirty_io() can simply test whether
bdi->tot_write_bandwidth is zero or not.
While this bumps the value of wb->avg_write_bandwidth to one when it
used to be zero, this shouldn't cause any meaningful behavior
difference.
bdi_has_dirty_io() is made an inline function which tests whether
->tot_write_bandwidth is non-zero. Also, WARN_ON_ONCE()'s on its
value are added to inode_wb_list_{move|del}_locked().
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
cgroup writeback support needs to keep track of the sum of
avg_write_bandwidth of all wb's (bdi_writeback's) with dirty inodes to
distribute write workload. This patch adds bdi->tot_write_bandwidth
and updates inode_wb_list_move_locked(), inode_wb_list_del_locked()
and wb_update_write_bandwidth() to adjust it as wb's gain and lose
dirty inodes and its avg_write_bandwidth gets updated.
As the update events are not synchronized with each other,
bdi->tot_write_bandwidth is an atomic_long_t.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:45 +0000 (17:13 -0400)]
writeback: implement WB_has_dirty_io wb_state flag
Currently, wb_has_dirty_io() determines whether a wb (bdi_writeback)
has any dirty inode by testing all three IO lists on each invocation
without actively keeping track. For cgroup writeback support, a
single bdi will host multiple wb's each of which will host dirty
inodes separately and we'll need to make bdi_has_dirty_io(), which
currently only represents the root wb, aggregate has_dirty_io from all
member wb's, which requires tracking transitions in has_dirty_io state
on each wb.
This patch introduces inode_wb_list_{move|del}_locked() to consolidate
IO list operations leaving queue_io() the only other function which
directly manipulates IO lists (via move_expired_inodes()). All three
functions are updated to call wb_io_lists_[de]populated() which keep
track of whether the wb has dirty inodes or not and record it using
the new WB_has_dirty_io flag. inode_wb_list_moved_locked()'s return
value indicates whether the wb had no dirty inodes before.
mark_inode_dirty() is restructured so that the return value of
inode_wb_list_move_locked() can be used for deciding whether to wake
up the wb.
While at it, change {bdi|wb}_has_dirty_io()'s return values to bool.
These functions were returning 0 and 1 before. Also, add a comment
explaining the synchronization of wb_state flags.
v2: Updated to accommodate b_dirty_time.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:44 +0000 (17:13 -0400)]
writeback: implement and use inode_congested()
In several places, bdi_congested() and its wrappers are used to
determine whether more IOs should be issued. With cgroup writeback
support, this question can't be answered solely based on the bdi
(backing_dev_info). It's dependent on whether the filesystem and bdi
support cgroup writeback and the blkcg the inode is associated with.
This patch implements inode_congested() and its wrappers which take
@inode and determines the congestion state considering cgroup
writeback. The new functions replace bdi_*congested() calls in places
where the query is about specific inode and task.
There are several filesystem users which also fit this criteria but
they should be updated when each filesystem implements cgroup
writeback support.
v2: Now that a given inode is associated with only one wb, congestion
state can be determined independent from the asking task. Drop
@task. Spotted by Vivek. Also, converted to take @inode instead
of @mapping and renamed to inode_congested().
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:43 +0000 (17:13 -0400)]
writeback, blkcg: propagate non-root blkcg congestion state
Now that bdi layer can handle per-blkcg bdi_writeback_congested state,
blk_{set|clear}_congested() can propagate non-root blkcg congestion
state to them.
This can be easily achieved by disabling the root_rl tests in
blk_{set|clear}_congested(). Note that we still need those tests when
!CONFIG_CGROUP_WRITEBACK as otherwise we'll end up flipping root blkcg
wb's congestion state for events happening on other blkcgs.
v2: Updated for bdi_writeback_congested.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
blk_{set|clear}_queue_congested() take @q and set or clear,
respectively, the congestion state of its bdi's root wb. Because bdi
used to be able to handle congestion state only on the root wb, the
callers of those functions tested whether the congestion is on the
root blkcg and skipped if not.
This is cumbersome and makes implementation of per cgroup
bdi_writeback congestion state propagation difficult. This patch
renames blk_{set|clear}_queue_congested() to
blk_{set|clear}_congested(), and makes them take request_list instead
of request_queue and test whether the specified request_list is the
root one before updating bdi_writeback congestion state. This makes
the tests in the callers unnecessary and simplifies them.
As there are no external users of these functions, the definitions are
moved from include/linux/blkdev.h to block/blk-core.c.
This patch doesn't introduce any noticeable behavior difference.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:41 +0000 (17:13 -0400)]
writeback: make congestion functions per bdi_writeback
Currently, all congestion functions take bdi (backing_dev_info) and
always operate on the root wb (bdi->wb) and the congestion state from
the block layer is propagated only for the root blkcg. This patch
introduces {set|clear}_wb_congested() and wb_congested() which take a
bdi_writeback_congested and bdi_writeback respectively. The bdi
counteparts are now wrappers invoking the wb based functions on
@bdi->wb.
While converting clear_bdi_congested() to clear_wb_congested(), the
local variable declaration order between @wqh and @bit is swapped for
cosmetic reason.
This patch just adds the new wb based functions. The following
patches will apply them.
v2: Updated for bdi_writeback_congested.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:40 +0000 (17:13 -0400)]
writeback: let balance_dirty_pages() work on the matching cgroup bdi_writeback
Currently, balance_dirty_pages() always work on bdi->wb. This patch
updates it to work on the wb (bdi_writeback) matching memcg and blkcg
of the current task as that's what the inode is being dirtied against.
balance_dirty_pages_ratelimited() now pins the current wb and passes
it to balance_dirty_pages().
As no filesystem has FS_CGROUP_WRITEBACK yet, this doesn't lead to
visible behavior differences.
v2: Updated for per-inode wb association.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:39 +0000 (17:13 -0400)]
writeback: attribute stats to the matching per-cgroup bdi_writeback
Until now, all WB_* stats were accounted against the root wb
(bdi_writeback), now that multiple wb (bdi_writeback) support is in
place, let's attributes the stats to the respective per-cgroup wb's.
As no filesystem has FS_CGROUP_WRITEBACK yet, this doesn't lead to
visible behavior differences.
v2: Updated for per-inode wb association.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:38 +0000 (17:13 -0400)]
writeback, blkcg: associate each blkcg_gq with the corresponding bdi_writeback_congested
A blkg (blkcg_gq) can be congested and decongested independently from
other blkgs on the same request_queue. Accordingly, for cgroup
writeback support, the congestion status at bdi (backing_dev_info)
should be split and updated separately from matching blkg's.
This patch prepares by adding blkg->wb_congested and associating a
blkg with its matching per-blkcg bdi_writeback_congested on creation.
v2: Updated to associate bdi_writeback_congested instead of
bdi_writeback.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:37 +0000 (17:13 -0400)]
writeback: make backing_dev_info host cgroup-specific bdi_writebacks
For the planned cgroup writeback support, on each bdi
(backing_dev_info), each memcg will be served by a separate wb
(bdi_writeback). This patch updates bdi so that a bdi can host
multiple wbs (bdi_writebacks).
On the default hierarchy, blkcg implicitly enables memcg. This allows
using memcg's page ownership for attributing writeback IOs, and every
memcg - blkcg combination can be served by its own wb by assigning a
dedicated wb to each memcg. This means that there may be multiple
wb's of a bdi mapped to the same blkcg. As congested state is per
blkcg - bdi combination, those wb's should share the same congested
state. This is achieved by tracking congested state via
bdi_writeback_congested structs which are keyed by blkcg.
bdi->wb remains unchanged and will keep serving the root cgroup.
cgwb's (cgroup wb's) for non-root cgroups are created on-demand or
looked up while dirtying an inode according to the memcg of the page
being dirtied or current task. Each cgwb is indexed on bdi->cgwb_tree
by its memcg id. Once an inode is associated with its wb, it can be
retrieved using inode_to_wb().
Currently, none of the filesystems has FS_CGROUP_WRITEBACK and all
pages will keep being associated with bdi->wb.
v3: inode_attach_wb() in account_page_dirtied() moved inside
mapping_cap_account_dirty() block where it's known to be !NULL.
Also, an unnecessary NULL check before kfree() removed. Both
detected by the kbuild bot.
v2: Updated so that wb association is per inode and wb is per memcg
rather than blkcg.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: kbuild test robot <fengguang.wu@intel.com> Cc: Dan Carpenter <dan.carpenter@oracle.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
cgroup writeback requires support from both bdi and filesystem sides.
Add BDI_CAP_CGROUP_WRITEBACK and FS_CGROUP_WRITEBACK to indicate
support and enable BDI_CAP_CGROUP_WRITEBACK on block based bdi's by
default. Also, define CONFIG_CGROUP_WRITEBACK which is enabled if
both MEMCG and BLK_CGROUP are enabled.
inode_cgwb_enabled() which determines whether a given inode's both bdi
and fs support cgroup writeback is added.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:35 +0000 (17:13 -0400)]
bdi: separate out congested state into a separate struct
Currently, a wb's (bdi_writeback) congestion state is carried in its
->state field; however, cgroup writeback support will require multiple
wb's sharing the same congestion state. This patch separates out
congestion state into its own struct - struct bdi_writeback_congested.
A new field wb field, wb_congested, points to its associated congested
struct. The default wb, bdi->wb, always points to bdi->wb_congested.
While this patch adds a layer of indirection, it doesn't introduce any
behavior changes.
Tejun Heo [Fri, 22 May 2015 21:13:33 +0000 (17:13 -0400)]
bdi: make inode_to_bdi() inline
Now that bdi definitions are moved to backing-dev-defs.h,
backing-dev.h can include blkdev.h and inline inode_to_bdi() without
worrying about introducing circular include dependency. The function
gets called from hot paths and fairly trivial.
This patch makes inode_to_bdi() and sb_is_blkdev_sb() that the
function calls inline. blockdev_superblock and noop_backing_dev_info
are EXPORT_GPL'd to allow the inline functions to be used from
modules.
While at it, make sb_is_blkdev_sb() return bool instead of int.
v2: Fixed typo in description as suggested by Jan.
Tejun Heo [Fri, 22 May 2015 21:13:32 +0000 (17:13 -0400)]
writeback: separate out include/linux/backing-dev-defs.h
With the planned cgroup writeback support, backing-dev related
declarations will be more widely used across block and cgroup;
unfortunately, including backing-dev.h from include/linux/blkdev.h
makes cyclic include dependency quite likely.
This patch separates out backing-dev-defs.h which only has the
essential definitions and updates blkdev.h to include it. c files
which need access to more backing-dev details now include
backing-dev.h directly. This takes backing-dev.h off the common
include dependency chain making it a lot easier to use it across block
and cgroup.
v2: fs/fat build failure fixed.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:31 +0000 (17:13 -0400)]
writeback: reorganize mm/backing-dev.c
Move wb_shutdown(), bdi_register(), bdi_register_dev(),
bdi_prune_sb(), bdi_remove_from_list() and bdi_unregister() so that
init / exit functions are grouped together. This will make updating
init / exit paths for cgroup writeback support easier.
This is pure source file reorganization.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:30 +0000 (17:13 -0400)]
writeback: move backing_dev_info->wb_lock and ->worklist into bdi_writeback
Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear. For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi. To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.
This patch moves bdi->wb_lock and ->worklist into wb.
* The lock protects bdi->worklist and bdi->wb.dwork scheduling. While
moving, rename it to wb->work_lock as wb->wb_lock is confusing.
Also, move wb->dwork downwards so that it's colocated with the new
->work_lock and ->work_list fields.
* bdi_wb_shutdown() is renamed to wb_shutdown() and now takes @wb.
The function contained parts which belong to the containing bdi
rather than the wb itself - testing cap_writeback_dirty and
bdi_remove_from_list() invocation. Those are moved to
bdi_unregister().
* bdi_wb_{init|exit}() are renamed to wb_{init|exit}().
Initializations of the moved bdi->wb_lock and ->work_list are
relocated from bdi_init() to wb_init().
* As there's still only one bdi_writeback per backing_dev_info, all
uses of bdi->state are mechanically replaced with bdi->wb.state
introducing no behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:29 +0000 (17:13 -0400)]
writeback: s/bdi/wb/ in mm/page-writeback.c
Writeback operations will now be per wb (bdi_writeback) instead of
bdi. Replace the relevant bdi references in symbol names and comments
with wb. This patch is purely cosmetic and doesn't make any
functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:28 +0000 (17:13 -0400)]
writeback: move bandwidth related fields from backing_dev_info into bdi_writeback
Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear. For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi. To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.
This patch moves bandwidth related fields from backing_dev_info into
bdi_writeback.
* The moved fields are: bw_time_stamp, dirtied_stamp, written_stamp,
write_bandwidth, avg_write_bandwidth, dirty_ratelimit,
balanced_dirty_ratelimit, completions and dirty_exceeded.
* writeback_chunk_size() and over_bground_thresh() now take @wb
instead of @bdi.
* Init/exits of the relocated fields are moved to bdi_wb_init/exit()
respectively. Note that explicit zeroing is dropped in the process
as wb's are cleared in entirety anyway.
* As there's still only one bdi_writeback per backing_dev_info, all
uses of bdi->stat[] are mechanically replaced with bdi->wb.stat[]
introducing no behavior changes.
v2: Typo in description fixed as suggested by Jan.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Jaegeuk Kim <jaegeuk@kernel.org> Cc: Steven Whitehouse <swhiteho@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:27 +0000 (17:13 -0400)]
writeback: move backing_dev_info->bdi_stat[] into bdi_writeback
Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear. For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi. To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.
This patch moves bdi->bdi_stat[] into wb.
* enum bdi_stat_item is renamed to wb_stat_item and the prefix of all
enums is changed from BDI_ to WB_.
* stat init is moved to bdi_wb_init() and bdi_wb_exit() is added and
frees stat.
* As there's still only one bdi_writeback per backing_dev_info, all
uses of bdi->stat[] are mechanically replaced with bdi->wb.stat[]
introducing no behavior changes.
Tejun Heo [Fri, 22 May 2015 21:13:26 +0000 (17:13 -0400)]
writeback: move backing_dev_info->state into bdi_writeback
Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear. For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi. To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.
This patch moves bdi->state into wb.
* enum bdi_state is renamed to wb_state and the prefix of all enums is
changed from BDI_ to WB_.
* Explicit zeroing of bdi->state is removed without adding zeoring of
wb->state as the whole data structure is zeroed on init anyway.
* As there's still only one bdi_writeback per backing_dev_info, all
uses of bdi->state are mechanically replaced with bdi->wb.state
introducing no behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: drbd-dev@lists.linbit.com Cc: Neil Brown <neilb@suse.de> Cc: Alasdair Kergon <agk@redhat.com> Cc: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Thu, 28 May 2015 00:00:02 +0000 (20:00 -0400)]
memcg: implement mem_cgroup_css_from_page()
Implement mem_cgroup_css_from_page() which returns the
cgroup_subsys_state of the memcg associated with a given page on the
default hierarchy. This will be used by cgroup writeback support.
This function assumes that page->mem_cgroup association doesn't change
until the page is released, which is true on the default hierarchy as
long as replace_page_cache_page() is not used. As the only user of
replace_page_cache_page() is FUSE which won't support cgroup writeback
for the time being, this works for now, and replace_page_cache_page()
will soon be updated so that the invariant actually holds.
Note that the RCU protected page->mem_cgroup access is consistent with
other usages across memcg but ultimately incorrect. These unlocked
accesses are missing required barriers. page->mem_cgroup should be
made an RCU pointer and updated and accessed using RCU operations.
v4: Instead of triggering WARN, return the root css on the traditional
hierarchies. This makes the function a lot easier to deal with
especially as there's no light way to synchronize against
hierarchy rebinding.
Tejun Heo [Fri, 22 May 2015 21:13:24 +0000 (17:13 -0400)]
blkcg: implement bio_associate_blkcg()
Currently, a bio can only be associated with the io_context and blkcg
of %current using bio_associate_current(). This is too restrictive
for cgroup writeback support. Implement bio_associate_blkcg() which
associates a bio with the specified blkcg.
bio_associate_blkcg() leaves the io_context unassociated.
bio_associate_current() is updated so that it considers a bio as
already associated if it has a blkcg_css, instead of an io_context,
associated with it.
Tejun Heo [Fri, 22 May 2015 21:13:23 +0000 (17:13 -0400)]
blkcg: implement task_get_blkcg_css()
Implement a wrapper around task_get_css() to acquire the blkcg css for
a given task. The wrapper is necessary for cgroup writeback support
as there will be places outside blkcg proper trying to acquire
blkcg_css and blkio_cgrp_id will be undefined when !CONFIG_BLK_CGROUP.
Tejun Heo [Fri, 22 May 2015 21:13:22 +0000 (17:13 -0400)]
cgroup, block: implement task_get_css() and use it in bio_associate_current()
bio_associate_current() currently open codes task_css() and
css_tryget_online() to find and pin $current's blkcg css. Abstract it
into task_get_css() which is implemented from cgroup side. As a task
is always associated with an online css for every subsystem except
while the css_set update is propagating, task_get_css() retries till
css_tryget_online() succeeds.
This is a cleanup and shouldn't lead to noticeable behavior changes.
Tejun Heo [Fri, 22 May 2015 21:13:21 +0000 (17:13 -0400)]
blkcg: add blkcg_root_css
Add global constant blkcg_root_css which points to &blkcg_root.css.
This will be used by cgroup writeback support. If blkcg is disabled,
it's defined as ERR_PTR(-EINVAL).
v2: The declarations moved to include/linux/blk-cgroup.h as suggested
by Vivek.
Tejun Heo [Fri, 22 May 2015 21:13:20 +0000 (17:13 -0400)]
memcg: add mem_cgroup_root_css
Add global mem_cgroup_root_css which points to the root memcg css.
This will be used by cgroup writeback support. If memcg is disabled,
it's defined as ERR_PTR(-EINVAL).
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org>
aCc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Tejun Heo [Fri, 22 May 2015 21:13:19 +0000 (17:13 -0400)]
blkcg: always create the blkcg_gq for the root blkcg
Currently, blkcg does a minor optimization where the root blkcg is
created when the first blkcg policy is activated on a queue and
destroyed on the deactivation of the last. On systems where blkcg is
configured but not used, this saves one blkcg_gq struct per queue. On
systems where blkcg is actually used, there's no difference. The only
case where this can lead to any meaninful, albeit still minute, save
in memory consumption is when all blkcg policies are deactivated after
being widely used in the system, which is a hihgly unlikely scenario.
The conditional existence of root blkcg_gq has already created several
bugs in blkcg and became an issue once again for the new per-cgroup
wb_congested mechanism for cgroup writeback support leading to a NULL
dereference when no blkcg policy is active. This is really not worth
bothering with. This patch makes blkcg always allocate and link the
root blkcg_gq and release it only on queue destruction.
Tejun Heo [Fri, 22 May 2015 21:13:18 +0000 (17:13 -0400)]
update !CONFIG_BLK_CGROUP dummies in include/linux/blk-cgroup.h
The header file will be used more widely with the pending cgroup
writeback support and the current set of dummy declarations aren't
enough to handle different config combinations. Update as follows.
* Drop the struct cgroup declaration. None of the dummy defs need it.
* Define blkcg as an empty struct instead of just declaring it.
* Wrap dummy function defs in CONFIG_BLOCK. Some functions use block
data types and none of them are to be used w/o block enabled.
Tejun Heo [Fri, 22 May 2015 21:13:17 +0000 (17:13 -0400)]
blkcg: move block/blk-cgroup.h to include/linux/blk-cgroup.h
cgroup aware writeback support will require exposing some of blkcg
details. In preprataion, move block/blk-cgroup.h to
include/linux/blk-cgroup.h. This patch is pure file move.
Greg Thelen [Fri, 22 May 2015 21:13:16 +0000 (17:13 -0400)]
memcg: add per cgroup dirty page accounting
When modifying PG_Dirty on cached file pages, update the new
MEM_CGROUP_STAT_DIRTY counter. This is done in the same places where
global NR_FILE_DIRTY is managed. The new memcg stat is visible in the
per memcg memory.stat cgroupfs file. The most recent past attempt at
this was http://thread.gmane.org/gmane.linux.kernel.cgroups/8632
The new accounting supports future efforts to add per cgroup dirty
page throttling and writeback. It also helps an administrator break
down a container's memory usage and provides evidence to understand
memcg oom kills (the new dirty count is included in memcg oom kill
messages).
The ability to move page accounting between memcg
(memory.move_charge_at_immigrate) makes this accounting more
complicated than the global counter. The existing
mem_cgroup_{begin,end}_page_stat() lock is used to serialize move
accounting with stat updates.
Typical update operation:
memcg = mem_cgroup_begin_page_stat(page)
if (TestSetPageDirty()) {
[...]
mem_cgroup_update_page_stat(memcg)
}
mem_cgroup_end_page_stat(memcg)
Summary of mem_cgroup_end_page_stat() overhead:
- Without CONFIG_MEMCG it's a no-op
- With CONFIG_MEMCG and no inter memcg task movement, it's just
rcu_read_lock()
- With CONFIG_MEMCG and inter memcg task movement, it's
rcu_read_lock() + spin_lock_irqsave()
A memcg parameter is added to several routines because their callers
now grab mem_cgroup_begin_page_stat() which returns the memcg later
needed by for mem_cgroup_update_page_stat().
Because mem_cgroup_begin_page_stat() may disable interrupts, some
adjustments are needed:
- move __mark_inode_dirty() from __set_page_dirty() to its caller.
__mark_inode_dirty() locking does not want interrupts disabled.
- use spin_lock_irqsave(tree_lock) rather than spin_lock_irq() in
__delete_from_page_cache(), replace_page_cache_page(),
invalidate_complete_page2(), and __remove_mapping().
Performance tests run on v4.0-rc1-36-g4f671fe2f952. Lower is better for
all metrics, they're all wall clock or cycle counts. The read and write
fault benchmarks just measure fault time, they do not include I/O time.
Tejun Heo [Fri, 22 May 2015 21:13:15 +0000 (17:13 -0400)]
page_writeback: revive cancel_dirty_page() in a restricted form
cancel_dirty_page() had some issues and b9ea25152e56 ("page_writeback:
clean up mess around cancel_dirty_page()") replaced it with
account_page_cleaned() which makes the caller responsible for clearing
the dirty bit; unfortunately, the planned changes for cgroup writeback
support requires synchronization between dirty bit manipulation and
stat updates. While we can open-code such synchronization in each
account_page_cleaned() callsite, that's gonna be unnecessarily awkward
and verbose.
This patch revives cancel_dirty_page() but in a more restricted form.
All it does is TestClearPageDirty() followed by account_page_cleaned()
invocation if the page was dirty. This helper covers all
account_page_cleaned() usages except for __delete_from_page_cache()
which is a special case anyway and left alone. As this leaves no
module user for account_page_cleaned(), EXPORT_SYMBOL() is dropped
from it.
This patch just revives cancel_dirty_page() as a trivial wrapper to
replace equivalent usages and doesn't introduce any functional
changes.
Keith Busch [Mon, 1 Jun 2015 15:29:53 +0000 (09:29 -0600)]
blk-mq: Shared tag enhancements
Storage controllers may expose multiple block devices that share hardware
resources managed by blk-mq. This patch enhances the shared tags so a
low-level driver can access the shared resources not tied to the unshared
h/w contexts. This way the LLD can dynamically add and delete disks and
request queues without having to track all the request_queue hctx's to
iterate outstanding tags.
Signed-off-by: Keith Busch <keith.busch@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Currently dm-multipath has to clone the bios for every request sent
to the lower devices, which wastes cpu cycles and ties down memory.
This patch instead adds a new REQ_CLONE flag that instructs req_bio_endio
to not complete bios attached to a request, which we set on clone
requests similar to bios in a flush sequence. With this change I/O
errors on a path failure only get propagated to dm-multipath, which
can then either resubmit the I/O or complete the bios on the original
request.
I've done some basic testing of this on a Linux target with ALUA support,
and it survives path failures during I/O nicely.
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Mike Snitzer [Fri, 22 May 2015 13:14:03 +0000 (09:14 -0400)]
block: remove management of bi_remaining when restoring original bi_end_io
Commit c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for
non-chains") regressed all existing callers that followed this pattern:
1) saving a bio's original bi_end_io
2) wiring up an intermediate bi_end_io
3) restoring the original bi_end_io from intermediate bi_end_io
4) calling bio_endio() to execute the restored original bi_end_io
The regression was due to BIO_CHAIN only ever getting set if
bio_inc_remaining() is called. For the above pattern it isn't set until
step 3 above (step 2 would've needed to establish BIO_CHAIN). As such
the first bio_endio(), in step 2 above, never decremented __bi_remaining
before calling the intermediate bi_end_io -- leaving __bi_remaining with
the value 1 instead of 0. When bio_inc_remaining() occurred during step
3 it brought it to a value of 2. When the second bio_endio() was
called, in step 4 above, it should've called the original bi_end_io but
it didn't because there was an extra reference that wasn't dropped (due
to atomic operations being optimized away since BIO_CHAIN wasn't set
upfront).
Fix this issue by removing the __bi_remaining management complexity for
all callers that use the above pattern -- bio_chain() is the only
interface that _needs_ to be concerned with __bi_remaining. For the
above pattern callers just expect the bi_end_io they set to get called!
Remove bio_endio_nodec() and also remove all bio_inc_remaining() calls
that aren't associated with the bio_chain() interface.
Also, the bio_inc_remaining() interface has been moved local to bio.c.
Fixes: c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for non-chains") Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Ming Lei [Wed, 6 May 2015 04:26:27 +0000 (12:26 +0800)]
block: replace trylock with mutex_lock in blkdev_reread_part()
The only possible problem of using mutex_lock() instead of trylock
is about deadlock.
If there aren't any locks held before calling blkdev_reread_part(),
deadlock can't be caused by this conversion.
If there are locks held before calling blkdev_reread_part(),
and if these locks arn't required in open, close handler and I/O
path, deadlock shouldn't be caused too.
Both user space's ioctl(BLKRRPART) and md_setup_drive() from
init/do_mounts_md.c belongs to the 1st case, so the conversion is safe
for the two cases.
For loop, the previous patches in this pathset has fixed the ABBA lock
dependency, so the conversion is OK.
For nbd, tx_lock is held when calling the function:
- both open and release won't hold the lock
- when blkdev_reread_part() is run, I/O thread has been stopped
already, so tx_lock won't be acquired in I/O path at that time.
- so the conversion won't cause deadlock for nbd
For dasd, both dasd_open(), dasd_release() and request function don't
acquire any mutex/semphone, so the conversion should be safe.
Reviewed-by: Christoph Hellwig <hch@lst.de> Tested-by: Jarod Wilson <jarod@redhat.com> Acked-by: Jarod Wilson <jarod@redhat.com> Signed-off-by: Ming Lei <ming.lei@canonical.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Jarod Wilson [Wed, 6 May 2015 04:26:22 +0000 (12:26 +0800)]
block: export blkdev_reread_part() and __blkdev_reread_part()
This patch exports blkdev_reread_part() for block drivers, also
introduce __blkdev_reread_part().
For some drivers, such as loop, reread of partitions can be run
from the release path, and bd_mutex may already be held prior to
calling ioctl_by_bdev(bdev, BLKRRPART, 0), so introduce
__blkdev_reread_part for use in such cases.
CC: Christoph Hellwig <hch@lst.de> CC: Jens Axboe <axboe@kernel.dk> CC: Tejun Heo <tj@kernel.org> CC: Alexander Viro <viro@zeniv.linux.org.uk> CC: Markus Pargmann <mpa@pengutronix.de> CC: Stefan Weinhuber <wein@de.ibm.com> CC: Stefan Haberland <stefan.haberland@de.ibm.com> CC: Sebastian Ott <sebott@linux.vnet.ibm.com> CC: Fabian Frederick <fabf@skynet.be> CC: Ming Lei <ming.lei@canonical.com> CC: David Herrmann <dh.herrmann@gmail.com> CC: Andrew Morton <akpm@linux-foundation.org> CC: Peter Zijlstra <peterz@infradead.org> CC: nbd-general@lists.sourceforge.net CC: linux-s390@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jarod Wilson <jarod@redhat.com> Signed-off-by: Ming Lei <ming.lei@canonical.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Stop abusing struct page functionality and the swap end_io handler, and
instead add a modified version of the blk-lib.c bio_batch helpers.
Also move the block I/O code into swap.c as they are directly tied into
each other.
Signed-off-by: Christoph Hellwig <hch@lst.de> Tested-by: Pavel Machek <pavel@ucw.cz> Tested-by: Ming Lin <mlin@kernel.org> Acked-by: Pavel Machek <pavel@ucw.cz> Acked-by: Rafael J. Wysocki <rjw@rjwysocki.net> Signed-off-by: Jens Axboe <axboe@fb.com>
Since the big barrier rewrite/removal in 2007 we never fail FLUSH or
FUA requests, which means we can remove the magic BIO_EOPNOTSUPP flag
to help propagating those to the buffer_head layer.
Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jeff Moyer <jmoyer@redhat.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@fb.com>
lockdep gets unhappy about the not disabling irqs when using the queue_lock
around it. Instead of trying to fix that up just switch to an atomic_t
and get rid of the lock.
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
Shaohua Li [Fri, 8 May 2015 17:51:33 +0000 (10:51 -0700)]
blk-mq: make plug work for mutiple disks and queues
Last patch makes plug work for multiple queue case. However it only
works for single disk case, because it assumes only one request in the
plug list. If a task is accessing multiple disks, eg MD/DM, the
assumption is wrong. Let blk_attempt_plug_merge() record request from
the same queue.
V2: use NULL parameter in !mq case. Fix a bug. Add comments in
blk_attempt_plug_merge to make it less (hopefully) confusion.
Cc: Jens Axboe <axboe@fb.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Shaohua Li [Fri, 8 May 2015 17:51:32 +0000 (10:51 -0700)]
blk-mq: do limited block plug for multiple queue case
plug is still helpful for workload with IO merge, but it can be harmful
otherwise especially with multiple hardware queues, as there is
(supposed) no lock contention in this case and plug can introduce
latency. For multiple queues, we do limited plug, eg plug only if there
is request merge. If a request doesn't have merge with following
request, the requet will be dispatched immediately.
V2: check blk_queue_nomerges() as suggested by Jeff.
Cc: Jens Axboe <axboe@fb.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Shaohua Li [Fri, 8 May 2015 17:51:31 +0000 (10:51 -0700)]
blk-mq: avoid re-initialize request which is failed in direct dispatch
If we directly issue a request and it fails, we use
blk_mq_merge_queue_io(). But we already assigned bio to a request in
blk_mq_bio_to_request. blk_mq_merge_queue_io shouldn't run
blk_mq_bio_to_request again.
Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Jeff Moyer [Fri, 8 May 2015 17:51:30 +0000 (10:51 -0700)]
blk-mq: fix plugging in blk_sq_make_request
The following appears in blk_sq_make_request:
/*
* If we have multiple hardware queues, just go directly to
* one of those for sync IO.
*/
We clearly don't have multiple hardware queues, here! This comment was
introduced with this commit 07068d5b8e (blk-mq: split make request
handler for multi and single queue):
We want slightly different behavior from them:
- On single queue devices, we currently use the per-process plug
for deferred IO and for merging.
- On multi queue devices, we don't use the per-process plug, but
we want to go straight to hardware for SYNC IO.
which is not equivalent. For the single queue case, that second half of
the && expression is always true. So, what I think was actually inteded
follows (and this more closely matches what is done in blk_queue_bio).
V2: delete the 'likely', which should not be a big deal
Signed-off-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Shaohua Li [Fri, 8 May 2015 17:51:29 +0000 (10:51 -0700)]
sched: always use blk_schedule_flush_plug in io_schedule_out
block plug callback could sleep, so we introduce a parameter
'from_schedule' and corresponding drivers can use it to destinguish a
schedule plug flush or a plug finish. Unfortunately io_schedule_out
still uses blk_flush_plug(). This causes below output (Note, I added a
might_sleep() in raid1_unplug to make it trigger faster, but the whole
thing doesn't matter if I add might_sleep). In raid1/10, this can cause
deadlock.
This patch makes io_schedule_out always uses blk_schedule_flush_plug.
This should only impact drivers (as far as I know, raid 1/10) which are
sensitive to the 'from_schedule' parameter.
Shaohua Li [Fri, 8 May 2015 17:51:28 +0000 (10:51 -0700)]
blk: clean up plug
Current code looks like inner plug gets flushed with a
blk_finish_plug(). Actually it's a nop. All requests/callbacks are added
to current->plug, while only outmost plug is assigned to current->plug.
So inner plug always has empty request/callback list, which makes
blk_flush_plug_list() a nop. This tries to make the code more clear.
Signed-off-by: Shaohua Li <shli@fb.com> Reviewed-by: Jeff Moyer <jmoyer@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
This removes the request types and hacks from the block code and into the
old IDE driver. There is a small amunt of code duplication due to this,
but it's not too bad.
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
block: move REQ_TYPE_ATA_TASKFILE and REQ_TYPE_ATA_PC to ide.h
These values are only used by the IDE driver, so move them into it
by allowing drivers to take cmd_type values after the first private
one. Note that we have to turn cmd_type into a plain unsigned integer
so that gcc doesn't complain about mismatching enum types.
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
bio: skip atomic inc/dec of ->bi_cnt for most use cases
Struct bio has a reference count that controls when it can be freed.
Most uses cases is allocating the bio, which then returns with a
single reference to it, doing IO, and then dropping that single
reference. We can remove this atomic_dec_and_test() in the completion
path, if nobody else is holding a reference to the bio.
If someone does call bio_get() on the bio, then we flag the bio as
now having valid count and that we must properly honor the reference
count when it's being put.
Tested-by: Robert Elliott <elliott@hp.com> Signed-off-by: Jens Axboe <axboe@fb.com>
bio: skip atomic inc/dec of ->bi_remaining for non-chains
Struct bio has an atomic ref count for chained bio's, and we use this
to know when to end IO on the bio. However, most bio's are not chained,
so we don't need to always introduce this atomic operation as part of
ending IO.
Add a helper to elevate the bi_remaining count, and flag the bio as
now actually needing the decrement at end_io time. Rename the field
to __bi_remaining to catch any current users of this doing the
incrementing manually.
For high IOPS workloads, this reduces the overhead of bio_endio()
substantially.
Tested-by: Robert Elliott <elliott@hp.com> Acked-by: Kent Overstreet <kent.overstreet@gmail.com> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
Pull crypto fixes from Herbert Xu:
"This fixes a build problem with bcm63xx and yet another fix to the
memzero_explicit function to ensure that the memset is not elided"
* git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6:
hwrng: bcm63xx - Fix driver compilation
lib: make memzero_explicit more robust against dead store elimination
Linus Torvalds [Tue, 5 May 2015 15:42:06 +0000 (08:42 -0700)]
Merge tag 'media/v4.1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
Pull media fixes from Mauro Carvalho Chehab:
"Three driver fixes:
- fix for omap4, fixing a regression due to a subsystem API that got
removed for 4.1 (commit efde234674d9);
- fix for one of the formats supported by Marvel ccic driver;
- fix rcar_vin driver that, when stopping abnormally, the driver
can't return from wait_for_completion"
* tag 'media/v4.1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media:
[media] v4l: omap4iss: Replace outdated OMAP4 control pad API with syscon
[media] media: soc_camera: rcar_vin: Fix wait_for_completion
[media] marvell-ccic: fix Y'CbCr ordering
Daniel Borkmann [Thu, 30 Apr 2015 02:13:52 +0000 (04:13 +0200)]
lib: make memzero_explicit more robust against dead store elimination
In commit 0b053c951829 ("lib: memzero_explicit: use barrier instead
of OPTIMIZER_HIDE_VAR"), we made memzero_explicit() more robust in
case LTO would decide to inline memzero_explicit() and eventually
find out it could be elimiated as dead store.
While using barrier() works well for the case of gcc, recent efforts
from LLVMLinux people suggest to use llvm as an alternative to gcc,
and there, Stephan found in a simple stand-alone user space example
that llvm could nevertheless optimize and thus elimitate the memset().
A similar issue has been observed in the referenced llvm bug report,
which is regarded as not-a-bug.
Based on some experiments, icc is a bit special on its own, while it
doesn't seem to eliminate the memset(), it could do so with an own
implementation, and then result in similar findings as with llvm.
The fix in this patch now works for all three compilers (also tested
with more aggressive optimization levels). Arguably, in the current
kernel tree it's more of a theoretical issue, but imho, it's better
to be pedantic about it.
It's clearly visible with gcc/llvm though, with the below code: if we
would have used barrier() only here, llvm would have omitted clearing,
not so with barrier_data() variant:
int main(void)
{
char buff[20];
memzero_explicit(buff, sizeof(buff));
return 0;
}
$ gcc -O2 test.c
$ gdb a.out
(gdb) disassemble main
Dump of assembler code for function main:
0x0000000000400400 <+0>: lea -0x28(%rsp),%rax
0x0000000000400405 <+5>: movq $0x0,-0x28(%rsp)
0x000000000040040e <+14>: movq $0x0,-0x20(%rsp)
0x0000000000400417 <+23>: movl $0x0,-0x18(%rsp)
0x000000000040041f <+31>: xor %eax,%eax
0x0000000000400421 <+33>: retq
End of assembler dump.
$ clang -O2 test.c
$ gdb a.out
(gdb) disassemble main
Dump of assembler code for function main:
0x00000000004004f0 <+0>: xorps %xmm0,%xmm0
0x00000000004004f3 <+3>: movaps %xmm0,-0x18(%rsp)
0x00000000004004f8 <+8>: movl $0x0,-0x8(%rsp)
0x0000000000400500 <+16>: lea -0x18(%rsp),%rax
0x0000000000400505 <+21>: xor %eax,%eax
0x0000000000400507 <+23>: retq
End of assembler dump.
As gcc, clang, but also icc defines __GNUC__, it's sufficient to define
this in compiler-gcc.h only to be picked up. For a fallback or otherwise
unsupported compiler, we define it as a barrier. Similarly, for ecc which
does not support gcc inline asm.
Reference: https://llvm.org/bugs/show_bug.cgi?id=15495 Reported-by: Stephan Mueller <smueller@chronox.de> Tested-by: Stephan Mueller <smueller@chronox.de> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Stephan Mueller <smueller@chronox.de> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Cc: mancha security <mancha1@zoho.com> Cc: Mark Charlebois <charlebm@gmail.com> Cc: Behan Webster <behanw@converseincode.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
projects / linux-beck.git / log