LIO target is a full featured in-kernel target framework with the
following feature set:
High-performance, non-blocking, multithreaded architecture with SIMD
support.
Advanced SCSI feature set:
* Persistent Reservations (PRs)
* Asymmetric Logical Unit Assignment (ALUA)
* Protocol and intra-nexus multiplexing, load-balancing and failover (MC/S)
* Full Error Recovery (ERL=0,1,2)
* Active/active task migration and session continuation (ERL=2)
* Thin LUN provisioning (UNMAP and WRITE_SAMExx)
Multiprotocol target plugins
Storage media independence:
* Virtualization of all storage media; transparent mapping of IO to LUNs
* No hard limits on number of LUNs per Target; maximum LUN size ~750 TB
* Backstores: SATA, SAS, SCSI, BluRay, DVD, FLASH, USB, ramdisk, etc.
Standards compliance:
* Full compliance with IETF (RFC 3720)
* Full implementation of SPC-4 PRs and ALUA
Significant code cleanups done by Christoph Hellwig.
[jejb: fix up for new block bdev exclusive interface. Minor fixes from
Randy Dunlap and Dan Carpenter.] Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org> Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Tejun Heo [Tue, 28 Dec 2010 15:20:47 +0000 (16:20 +0100)]
[SCSI] sd,sr: kill compat SDEV_MEDIA_CHANGE event
SDEV_MEDIA_CHANGE event was first added by commit a341cd0f (SCSI: add
asynchronous event notification API) for SATA AN support and then
extended to cover generic media change events by commit 285e9670
([SCSI] sr,sd: send media state change modification events).
This event was mapped to block device in userland with all properties
stripped to simulate CHANGE event on the block device, which, in turn,
was used to trigger further userspace action on media change.
The recent addition of disk event framework kept this event for
backward compatibility but it turns out to be unnecessary and causes
erratic and inefficient behavior. The new disk event generates proper
events on the block devices and the compat events are mapped to block
device with all properties stripped, so the block device ends up
generating multiple duplicate events for single actual event.
This patch removes the compat event generation from both sr and sd as
suggested by Kay Sievers. Both existing and newer versions of udev
and the associated tools will behave better with the removal of these
events as they from the beginning were expecting events on the block
devices.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Kay Sievers <kay.sievers@vrfy.org> Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Tejun Heo [Sat, 18 Dec 2010 17:42:23 +0000 (18:42 +0100)]
[SCSI] sd: implement sd_check_events()
Replace sd_media_change() with sd_check_events().
* Move media removed logic into set_media_not_present() and
media_not_present() and set sdev->changed iff an existing media is
removed or the device indicates UNIT_ATTENTION.
* Make sd_check_events() sets sdev->changed if previously missing
media becomes present.
* Event is reported only if sdev->changed is set.
This makes media presence event reported if scsi_disk->media_present
actually changed or the device indicated UNIT_ATTENTION. For backward
compatibility, SDEV_EVT_MEDIA_CHANGE is generated each time
sd_check_events() detects media change event.
Linus Torvalds [Fri, 14 Jan 2011 04:15:35 +0000 (20:15 -0800)]
Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6
* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6: (59 commits)
ACPI / PM: Fix build problems for !CONFIG_ACPI related to NVS rework
ACPI: fix resource check message
ACPI / Battery: Update information on info notification and resume
ACPI: Drop device flag wake_capable
ACPI: Always check if _PRW is present before trying to evaluate it
ACPI / PM: Check status of power resources under mutexes
ACPI / PM: Rename acpi_power_off_device()
ACPI / PM: Drop acpi_power_nocheck
ACPI / PM: Drop acpi_bus_get_power()
Platform / x86: Make fujitsu_laptop use acpi_bus_update_power()
ACPI / Fan: Rework the handling of power resources
ACPI / PM: Register power resource devices as soon as they are needed
ACPI / PM: Register acpi_power_driver early
ACPI / PM: Add function for updating device power state consistently
ACPI / PM: Add function for device power state initialization
ACPI / PM: Introduce __acpi_bus_get_power()
ACPI / PM: Introduce function for refcounting device power resources
ACPI / PM: Add functions for manipulating lists of power resources
ACPI / PM: Prevent acpi_power_get_inferred_state() from making changes
ACPICA: Update version to 20101209
...
Linus Torvalds [Fri, 14 Jan 2011 04:15:18 +0000 (20:15 -0800)]
Merge branch 'idle-release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-idle-2.6
* 'idle-release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-idle-2.6:
cpuidle/x86/perf: fix power:cpu_idle double end events and throw cpu_idle events from the cpuidle layer
intel_idle: open broadcast clock event
cpuidle: CPUIDLE_FLAG_CHECK_BM is omap3_idle specific
cpuidle: CPUIDLE_FLAG_TLB_FLUSHED is specific to intel_idle
cpuidle: delete unused CPUIDLE_FLAG_SHALLOW, BALANCED, DEEP definitions
SH, cpuidle: delete use of NOP CPUIDLE_FLAGS_SHALLOW
cpuidle: delete NOP CPUIDLE_FLAG_POLL
ACPI: processor_idle: delete use of NOP CPUIDLE_FLAGs
cpuidle: Rename X86 specific idle poll state[0] from C0 to POLL
ACPI, intel_idle: Cleanup idle= internal variables
cpuidle: Make cpuidle_enable_device() call poll_idle_init()
intel_idle: update Sandy Bridge core C-state residency targets
Linus Torvalds [Fri, 14 Jan 2011 04:14:13 +0000 (20:14 -0800)]
Merge branch 'vfs-scale-working' of git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin
* 'vfs-scale-working' of git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin:
fs: fix do_last error case when need_reval_dot
nfs: add missing rcu-walk check
fs: hlist UP debug fixup
fs: fix dropping of rcu-walk from force_reval_path
fs: force_reval_path drop rcu-walk before d_invalidate
fs: small rcu-walk documentation fixes
Fixed up trivial conflicts in Documentation/filesystems/porting
J. R. Okajima [Fri, 14 Jan 2011 03:56:04 +0000 (03:56 +0000)]
fs: fix do_last error case when need_reval_dot
When open(2) without O_DIRECTORY opens an existing dir, it should return
EISDIR. In do_last(), the variable 'error' is initialized EISDIR, but it
is changed by d_revalidate() which returns any positive to represent
'the target dir is valid.'
Should we keep and return the initialized 'error' in this case.
Linus Torvalds [Fri, 14 Jan 2011 02:46:48 +0000 (18:46 -0800)]
Merge branch 'stable/gntdev' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen
* 'stable/gntdev' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
xen/p2m: Fix module linking error.
xen p2m: clear the old pte when adding a page to m2p_override
xen gntdev: use gnttab_map_refs and gnttab_unmap_refs
xen: introduce gnttab_map_refs and gnttab_unmap_refs
xen p2m: transparently change the p2m mappings in the m2p override
xen/gntdev: Fix circular locking dependency
xen/gntdev: stop using "token" argument
xen: gntdev: move use of GNTMAP_contains_pte next to the map_op
xen: add m2p override mechanism
xen: move p2m handling to separate file
xen/gntdev: add VM_PFNMAP to vma
xen/gntdev: allow usermode to map granted pages
xen: define gnttab_set_map_op/unmap_op
Linus Torvalds [Fri, 14 Jan 2011 02:44:52 +0000 (18:44 -0800)]
Merge branch 'stable/platform-pci-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen
* 'stable/platform-pci-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
xen-platform: Fix compile errors if CONFIG_PCI is not enabled.
xen: rename platform-pci module to xen-platform-pci.
xen-platform: use PCI interfaces to request IO and MEM resources.
Fix the expression, and also avoid a dependency between bit spinlock
implementation and list bl code (list code shouldn't know anything
except that bit 0 is set when adding and removing elements). Eventually
if a good use case comes up, we might use this list to store 1 or more
arbitrary bits of data, so it really shouldn't be tied to locking either,
but for now they are helpful for debugging.
Nick Piggin [Fri, 14 Jan 2011 02:36:19 +0000 (02:36 +0000)]
fs: fix dropping of rcu-walk from force_reval_path
As J. R. Okajima noted, force_reval_path passes in the same dentry to
d_revalidate as the one in the nameidata structure (other callers pass in a
child), so the locking breaks. This can oops with a chrooted nfs mount, for
example. Similarly there can be other problems with revalidating a dentry
which is already in nameidata of the path walk.
Nick Piggin [Fri, 14 Jan 2011 02:35:53 +0000 (02:35 +0000)]
fs: force_reval_path drop rcu-walk before d_invalidate
d_revalidate can return in rcu-walk mode even when it returns 0. We can't just
call any old dcache function on rcu-walk dentry (the dentry is unstable, so
even through d_lock can safely be taken, the result may no longer be what we
expect -- careful re-checks would be required). So just drop rcu in this case.
(I missed this conversion when switching to the rcu-walk convention that Linus
suggested)
In the current implementation mem_cgroup_end_migration() decides whether
the page migration has succeeded or not by checking "oldpage->mapping".
But if we are tring to migrate a shmem swapcache, the page->mapping of it
is NULL from the begining, so the check would be invalid. As a result,
mem_cgroup_end_migration() assumes the migration has succeeded even if
it's not, so "newpage" would be freed while it's not uncharged.
This patch fixes it by passing mem_cgroup_end_migration() the result of
the page migration.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Jesper Juhl [Thu, 13 Jan 2011 23:47:42 +0000 (15:47 -0800)]
memcg: use [kv]zalloc[_node] rather than [kv]malloc+memset
In mem_cgroup_alloc() we currently do either kmalloc() or vmalloc() then
followed by memset() to zero the memory. This can be more efficiently
achieved by using kzalloc() and vzalloc(). There's also one situation
where we can use kzalloc_node() - this is what's new in this version of
the patch.
Commit b1dd693e ("memcg: avoid deadlock between move charge and
try_charge()") can cause another deadlock about mmap_sem on task migration
if cpuset and memcg are mounted onto the same mount point.
After the commit, cgroup_attach_task() has sequence like:
We can cause deadlock at (2) because we've already aquire the mmap_sem at (1).
But the commit itself is necessary to fix deadlocks which have existed
before the commit like:
Ex.1)
move charge | try charge
--------------------------------------+------------------------------
mem_cgroup_can_attach() | down_write(&mmap_sem)
mc.moving_task = current | ..
mem_cgroup_precharge_mc() | __mem_cgroup_try_charge()
mem_cgroup_count_precharge() | prepare_to_wait()
down_read(&mmap_sem) | if (mc.moving_task)
-> cannot aquire the lock | -> true
| schedule()
| -> move charge should wake it up
Ex.2)
move charge | try charge
--------------------------------------+------------------------------
mem_cgroup_can_attach() |
mc.moving_task = current |
mem_cgroup_precharge_mc() |
mem_cgroup_count_precharge() |
down_read(&mmap_sem) |
.. |
up_read(&mmap_sem) |
| down_write(&mmap_sem)
mem_cgroup_move_task() | ..
mem_cgroup_move_charge() | __mem_cgroup_try_charge()
down_read(&mmap_sem) | prepare_to_wait()
-> cannot aquire the lock | if (mc.moving_task)
| -> true
| schedule()
| -> move charge should wake it up
This patch fixes all of these problems by:
1. revert the commit.
2. To fix the Ex.1, we set mc.moving_task after mem_cgroup_count_precharge()
has released the mmap_sem.
3. To fix the Ex.2, we use down_read_trylock() instead of down_read() in
mem_cgroup_move_charge() and, if it has failed to aquire the lock, cancel
all extra charges, wake up all waiters, and retry trylock.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Reported-by: Ben Blum <bblum@andrew.cmu.edu> Cc: Miao Xie <miaox@cn.fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Paul Menage <menage@google.com> Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Johannes Weiner [Thu, 13 Jan 2011 23:47:39 +0000 (15:47 -0800)]
memcg: fix unit mismatch in memcg oom limit calculation
Adding the number of swap pages to the byte limit of a memory control
group makes no sense. Convert the pages to bytes before adding them.
The only user of this code is the OOM killer, and the way it is used means
that the error results in a higher OOM badness value. Since the cgroup
limit is the same for all tasks in the cgroup, the error should have no
practical impact at the moment.
But let's not wait for future or changing users to trip over it.
memcg: add lock to synchronize page accounting and migration
Introduce a new bit spin lock, PCG_MOVE_LOCK, to synchronize the page
accounting and migration code. This reworks the locking scheme of
_update_stat() and _move_account() by adding new lock bit PCG_MOVE_LOCK,
which is always taken under IRQ disable.
1. If pages are being migrated from a memcg, then updates to that
memcg page statistics are protected by grabbing PCG_MOVE_LOCK using
move_lock_page_cgroup(). In an upcoming commit, memcg dirty page
accounting will be updating memcg page accounting (specifically: num
writeback pages) from IRQ context (softirq). Avoid a deadlocking
nested spin lock attempt by disabling irq on the local processor when
grabbing the PCG_MOVE_LOCK.
2. lock for update_page_stat is used only for avoiding race with
move_account(). So, IRQ awareness of lock_page_cgroup() itself is not
a problem. The problem is between mem_cgroup_update_page_stat() and
mem_cgroup_move_account_page().
Trade-off:
* Changing lock_page_cgroup() to always disable IRQ (or
local_bh) has some impacts on performance and I think
it's bad to disable IRQ when it's not necessary.
* adding a new lock makes move_account() slower. Score is
here.
Performance Impact: moving a 8G anon process.
Before:
real 0m0.792s
user 0m0.000s
sys 0m0.780s
After:
real 0m0.854s
user 0m0.000s
sys 0m0.842s
This score is bad but planned patches for optimization can reduce
this impact.
Greg Thelen [Thu, 13 Jan 2011 23:47:37 +0000 (15:47 -0800)]
memcg: create extensible page stat update routines
Replace usage of the mem_cgroup_update_file_mapped() memcg
statistic update routine with two new routines:
* mem_cgroup_inc_page_stat()
* mem_cgroup_dec_page_stat()
As before, only the file_mapped statistic is managed. However, these more
general interfaces allow for new statistics to be more easily added. New
statistics are added with memcg dirty page accounting.
Greg Thelen [Thu, 13 Jan 2011 23:47:35 +0000 (15:47 -0800)]
memcg: add page_cgroup flags for dirty page tracking
This patchset provides the ability for each cgroup to have independent
dirty page limits.
Limiting dirty memory is like fixing the max amount of dirty (hard to
reclaim) page cache used by a cgroup. So, in case of multiple cgroup
writers, they will not be able to consume more than their designated share
of dirty pages and will be forced to perform write-out if they cross that
limit.
The patches are based on a series proposed by Andrea Righi in Mar 2010.
Overview:
- Add page_cgroup flags to record when pages are dirty, in writeback, or nfs
unstable.
- Extend mem_cgroup to record the total number of pages in each of the
interesting dirty states (dirty, writeback, unstable_nfs).
- Add dirty parameters similar to the system-wide /proc/sys/vm/dirty_*
limits to mem_cgroup. The mem_cgroup dirty parameters are accessible
via cgroupfs control files.
- Consider both system and per-memcg dirty limits in page writeback when
deciding to queue background writeback or block for foreground writeback.
Known shortcomings:
- When a cgroup dirty limit is exceeded, then bdi writeback is employed to
writeback dirty inodes. Bdi writeback considers inodes from any cgroup, not
just inodes contributing dirty pages to the cgroup exceeding its limit.
- When memory.use_hierarchy is set, then dirty limits are disabled. This is a
implementation detail. An enhanced implementation is needed to check the
chain of parents to ensure that no dirty limit is exceeded.
Performance data:
- A page fault microbenchmark workload was used to measure performance, which
can be called in read or write mode:
f = open(foo. $cpu)
truncate(f, 4096)
alarm(60)
while (1) {
p = mmap(f, 4096)
if (write)
*p = 1
else
x = *p
munmap(p)
}
- The workload was called for several points in the patch series in different
modes:
- s_read is a single threaded reader
- s_write is a single threaded writer
- p_read is a 16 thread reader, each operating on a different file
- p_write is a 16 thread writer, each operating on a different file
- Measurements were collected on a 16 core non-numa system using "perf stat
--repeat 3". The -a option was used for parallel (p_*) runs.
- All numbers are page fault rate (M/sec). Higher is better.
- To compare the performance of a kernel without non-memcg compare the first and
last rows, neither has memcg configured. The first row does not include any
of these memcg patches.
- To compare the performance of using memcg dirty limits, compare the baseline
(2nd row titled "w/ memcg") with the the code and memcg enabled (2nd to last
row titled "all patches").
Shaohua Li [Thu, 13 Jan 2011 23:47:34 +0000 (15:47 -0800)]
mm: batch activate_page() to reduce lock contention
The zone->lru_lock is heavily contented in workload where activate_page()
is frequently used. We could do batch activate_page() to reduce the lock
contention. The batched pages will be added into zone list when the pool
is full or page reclaim is trying to drain them.
For example, in a 4 socket 64 CPU system, create a sparse file and 64
processes, processes shared map to the file. Each process read access the
whole file and then exit. The process exit will do unmap_vmas() and cause
a lot of activate_page() call. In such workload, we saw about 58% total
time reduction with below patch. Other workloads with a lot of
activate_page also benefits a lot too.
Hugh Dickins [Thu, 13 Jan 2011 23:47:31 +0000 (15:47 -0800)]
mm: fix hugepage migration
2.6.37 added an unmap_and_move_huge_page() for memory failure recovery,
but its anon_vma handling was still based around the 2.6.35 conventions.
Update it to use page_lock_anon_vma, get_anon_vma, page_unlock_anon_vma,
drop_anon_vma in the same way as we're now changing unmap_and_move().
I don't particularly like to propose this for stable when I've not seen
its problems in practice nor tested the solution: but it's clearly out of
synch at present.
Hugh Dickins [Thu, 13 Jan 2011 23:47:30 +0000 (15:47 -0800)]
mm: fix migration hangs on anon_vma lock
Increased usage of page migration in mmotm reveals that the anon_vma
locking in unmap_and_move() has been deficient since 2.6.36 (or even
earlier). Review at the time of f18194275c39835cb84563500995e0d503a32d9a
("mm: fix hang on anon_vma->root->lock") missed the issue here: the
anon_vma to which we get a reference may already have been freed back to
its slab (it is in use when we check page_mapped, but that can change),
and so its anon_vma->root may be switched at any moment by reuse in
anon_vma_prepare.
Perhaps we could fix that with a get_anon_vma_unless_zero(), but let's
not: just rely on page_lock_anon_vma() to do all the hard thinking for us,
then we don't need any rcu read locking over here.
In removing the rcu_unlock label: since PageAnon is a bit in
page->mapping, it's impossible for a !page->mapping page to be anon; but
insert VM_BUG_ON in case the implementation ever changes.
Eric B Munson [Thu, 13 Jan 2011 23:47:28 +0000 (15:47 -0800)]
hugetlb: fix handling of parse errors in sysfs
When parsing changes to the huge page pool sizes made from userspace via
the sysfs interface, bogus input values are being covered up by
nr_hugepages_store_common and nr_overcommit_hugepages_store returning 0
when strict_strtoul returns an error. This can cause an infinite loop in
the nr_hugepages_store code. This patch changes the return value for
these functions to -EINVAL when strict_strtoul returns an error.
Signed-off-by: Eric B Munson <emunson@mgebm.net> Reported-by: CAI Qian <caiqian@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Eric B Munson <emunson@mgebm.net> Cc: Michal Hocko <mhocko@suse.cz> Cc: Nishanth Aravamudan <nacc@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Eric B Munson [Thu, 13 Jan 2011 23:47:27 +0000 (15:47 -0800)]
hugetlb: do not allow pagesize >= MAX_ORDER pool adjustment
Huge pages with order >= MAX_ORDER must be allocated at boot via the
kernel command line, they cannot be allocated or freed once the kernel is
up and running. Currently we allow values to be written to the sysfs and
sysctl files controling pool size for these huge page sizes. This patch
makes the store functions for nr_hugepages and nr_overcommit_hugepages
return -EINVAL when the pool for a page size >= MAX_ORDER is changed.
[akpm@linux-foundation.org: avoid multiple return paths in nr_hugepages_store_common()]
[caiqian@redhat.com: add checking in hugetlb_overcommit_handler()] Signed-off-by: Eric B Munson <emunson@mgebm.net> Reported-by: CAI Qian <caiqian@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Nishanth Aravamudan <nacc@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Michal Hocko [Thu, 13 Jan 2011 23:47:26 +0000 (15:47 -0800)]
hugetlb: check the return value of string conversion in sysctl handler
proc_doulongvec_minmax may fail if the given buffer doesn't represent a
valid number. If we provide something invalid we will initialize the
resulting value (nr_overcommit_huge_pages in this case) to a random value
from the stack.
The issue was introduced by a3d0c6aa when the default handler has been
replaced by the helper function where we do not check the return value.
mm/dmapool.c: take lock only once in dma_pool_free()
dma_pool_free() scans for the page to free in the pool list holding the
pool lock. Then it releases the lock basically to acquire it immediately
again. Modify the code to only take the lock once.
This will do some additional loops and computations with the lock held in
if memory debugging is activated. If it is not activated the only new
operations with this lock is one if and one substraction.
Jiri Kosina [Thu, 13 Jan 2011 23:47:23 +0000 (15:47 -0800)]
brk: fix min_brk lower bound computation for COMPAT_BRK
Even if CONFIG_COMPAT_BRK is set in the kernel configuration, it can still
be overriden by randomize_va_space sysctl.
If this is the case, the min_brk computation in sys_brk() implementation
is wrong, as it solely takes into account COMPAT_BRK setting, assuming
that brk start is not randomized. But that might not be the case if
randomize_va_space sysctl has been set to '2' at the time the binary has
been loaded from disk.
In such case, the check has to be done in a same way as in
!CONFIG_COMPAT_BRK case.
In addition to that, the check for the COMPAT_BRK case introduced back in a5b4592c ("brk: make sys_brk() honor COMPAT_BRK when computing lower
bound") is slightly wrong -- the lower bound shouldn't be mm->end_code,
but mm->end_data instead, as that's where the legacy applications expect
brk section to start (i.e. immediately after last global variable).
Jesper Juhl [Thu, 13 Jan 2011 23:47:22 +0000 (15:47 -0800)]
mm/hugetlb.c: fix error-path memory leak in nr_hugepages_store_common()
The NODEMASK_ALLOC macro may dynamically allocate memory for its second
argument ('nodes_allowed' in this context).
In nr_hugepages_store_common() we may abort early if strict_strtoul()
fails, but in that case we do not free the memory already allocated to
'nodes_allowed', causing a memory leak.
This patch closes the leak by freeing the memory in the error path.
[akpm@linux-foundation.org: use NODEMASK_FREE, per Minchan Kim] Signed-off-by: Jesper Juhl <jj@chaosbits.net> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Mel Gorman [Thu, 13 Jan 2011 23:47:21 +0000 (15:47 -0800)]
mm: migration: use rcu_dereference_protected when dereferencing the radix tree slot during file page migration
migrate_pages() -> unmap_and_move() only calls rcu_read_lock() for
anonymous pages, as introduced by git commit 989f89c57e6361e7d16fbd9572b5da7d313b073d ("fix rcu_read_lock() in page
migraton"). The point of the RCU protection there is part of getting a
stable reference to anon_vma and is only held for anon pages as file pages
are locked which is sufficient protection against freeing.
However, while a file page's mapping is being migrated, the radix tree is
double checked to ensure it is the expected page. This uses
radix_tree_deref_slot() -> rcu_dereference() without the RCU lock held
triggering the following warning.
This patch introduces radix_tree_deref_slot_protected() which calls
rcu_dereference_protected(). Users of it must pass in the
mapping->tree_lock that is protecting this dereference. Holding the tree
lock protects against parallel updaters of the radix tree meaning that
rcu_dereference_protected is allowable.
[akpm@linux-foundation.org: remove unneeded casts] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Milton Miller <miltonm@bga.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: <stable@kernel.org> [2.6.37.early] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:19 +0000 (15:47 -0800)]
thp: KSM on THP
This makes KSM full operational with THP pages. Subpages are scanned
while the hugepage is still in place and delivering max cpu performance,
and only if there's a match and we're going to deduplicate memory, the
single hugepages with the subpage match is split.
There will be no false sharing between ksmd and khugepaged. khugepaged
won't collapse 2m virtual regions with KSM pages inside. ksmd also should
only split pages when the checksum matches and we're likely to split an
hugepage for some long living ksm page (usual ksm heuristic to avoid
sharing pages that get de-cowed).
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:18 +0000 (15:47 -0800)]
thp: khugepaged: make khugepaged aware about madvise
MADV_HUGEPAGE and MADV_NOHUGEPAGE were fully effective only if run after
mmap and before touching the memory. While this is enough for most
usages, it's little effort to make madvise more dynamic at runtime on an
existing mapping by making khugepaged aware about madvise.
MADV_HUGEPAGE: register in khugepaged immediately without waiting a page
fault (that may not ever happen if all pages are already mapped and the
"enabled" knob was set to madvise during the initial page faults).
MADV_NOHUGEPAGE: skip vmas marked VM_NOHUGEPAGE in khugepaged to stop
collapsing pages where not needed.
[akpm@linux-foundation.org: tweak comment] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:17 +0000 (15:47 -0800)]
thp: madvise(MADV_NOHUGEPAGE)
Add madvise MADV_NOHUGEPAGE to mark regions that are not important to be
hugepage backed. Return -EINVAL if the vma is not of an anonymous type,
or the feature isn't built into the kernel. Never silently return
success.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:16 +0000 (15:47 -0800)]
thp: fix memory-failure hugetlbfs vs THP collision
hugetlbfs was changed to allow memory failure to migrate the hugetlbfs
pages and that broke THP as split_huge_page was then called on hugetlbfs
pages too.
compound_head/order was also run unsafe on THP pages that can be splitted
at any time.
All compound_head() invocations in memory-failure.c that are run on pages
that aren't pinned and that can be freed and reused from under us (while
compound_head is running) are buggy because compound_head can return a
dangling pointer, but I'm not fixing this as this is a generic
memory-failure bug not specific to THP but it applies to hugetlbfs too, so
I can fix it later after THP is merged upstream.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rik van Riel [Thu, 13 Jan 2011 23:47:13 +0000 (15:47 -0800)]
thp: scale nr_rotated to balance memory pressure
Make sure we scale up nr_rotated when we encounter a referenced
transparent huge page. This ensures pageout scanning balance is not
distorted when there are huge pages on the LRU.
Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rik van Riel [Thu, 13 Jan 2011 23:47:13 +0000 (15:47 -0800)]
thp: fix anon memory statistics with transparent hugepages
Count each transparent hugepage as HPAGE_PMD_NR pages in the LRU
statistics, so the Active(anon) and Inactive(anon) statistics in
/proc/meminfo are correct.
Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rik van Riel [Thu, 13 Jan 2011 23:47:12 +0000 (15:47 -0800)]
thp: disable transparent hugepages by default on small systems
On small systems, the extra memory used by the anti-fragmentation memory
reserve and simply because huge pages are smaller than large pages can
easily outweigh the benefits of less TLB misses.
A less obvious concern is if run on a NUMA machine with asymmetric node
sizes and one of them is very small. The reserve could make the node
unusable.
In case of the crashdump kernel, OOMs have been observed due to the
anti-fragmentation memory reserve taking up a large fraction of the
crashdump image.
This patch disables transparent hugepages on systems with less than 1GB of
RAM, but the hugepage subsystem is fully initialized so administrators can
enable THP through /sys if desired.
Signed-off-by: Rik van Riel <riel@redhat.com> Acked-by: Avi Kiviti <avi@redhat.com> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:11 +0000 (15:47 -0800)]
thp: use compaction for all allocation orders
It makes no sense not to enable compaction for small order pages as we
don't want to end up with bad order 2 allocations and good and graceful
order 9 allocations.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:11 +0000 (15:47 -0800)]
thp: use compaction in kswapd for GFP_ATOMIC order > 0
This takes advantage of memory compaction to properly generate pages of
order > 0 if regular page reclaim fails and priority level becomes more
severe and we don't reach the proper watermarks.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:10 +0000 (15:47 -0800)]
thp: freeze khugepaged and ksmd
It's unclear why schedule friendly kernel threads can't be taken away by
the CPU through the scheduler itself. It's safer to stop them as they can
trigger memory allocation, if kswapd also freezes itself to avoid
generating I/O they have too.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:10 +0000 (15:47 -0800)]
thp: mmu_notifier_test_young
For GRU and EPT, we need gup-fast to set referenced bit too (this is why
it's correct to return 0 when shadow_access_mask is zero, it requires
gup-fast to set the referenced bit). qemu-kvm access already sets the
young bit in the pte if it isn't zero-copy, if it's zero copy or a shadow
paging EPT minor fault we relay on gup-fast to signal the page is in
use...
We also need to check the young bits on the secondary pagetables for NPT
and not nested shadow mmu as the data may never get accessed again by the
primary pte.
Without this closer accuracy, we'd have to remove the heuristic that
avoids collapsing hugepages in hugepage virtual regions that have not even
a single subpage in use.
->test_young is full backwards compatible with GRU and other usages that
don't have young bits in pagetables set by the hardware and that should
nuke the secondary mmu mappings when ->clear_flush_young runs just like
EPT does.
Removing the heuristic that checks the young bit in
khugepaged/collapse_huge_page completely isn't so bad either probably but
I thought it was worth it and this makes it reliable.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:09 +0000 (15:47 -0800)]
thp: don't allow transparent hugepage support without PSE
Archs implementing Transparent Hugepage Support must implement a function
called has_transparent_hugepage to be sure the virtual or physical CPU
supports Transparent Hugepages.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:08 +0000 (15:47 -0800)]
thp: avoid breaking huge pmd invariants in case of vma_adjust failures
An huge pmd can only be mapped if the corresponding 2M virtual range is
fully contained in the vma. At times the VM calls split_vma twice, if the
first split_vma succeeds and the second fail, the first split_vma remains
in effect and it's not rolled back. For split_vma or vma_adjust to fail
an allocation failure is needed so it's a very unlikely event (the out of
memory killer would normally fire before any allocation failure is visible
to kernel and userland and if an out of memory condition happens it's
unlikely to happen exactly here). Nevertheless it's safer to ensure that
no huge pmd can be left around if the vma is adjusted in a way that can't
fit hugepages anymore at the new vm_start/vm_end address.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:07 +0000 (15:47 -0800)]
thp: select CONFIG_COMPACTION if TRANSPARENT_HUGEPAGE enabled
With transparent hugepage support we need compaction for the "defrag"
sysfs controls to be effective.
At the moment THP hangs the system if COMPACTION isn't selected, as
without COMPACTION lumpy reclaim wouldn't be entirely disabled. So at the
moment it's not orthogonal. When lumpy will be removed from the VM I can
remove the select COMPACTION in theory, but then 99% of THP users would be
still doing a mistake in disabling compaction, even if the mistake won't
return in fatal runtime but just slightly degraded performance. So from a
theoretical standpoing forcing the below select is not needed (the
dependency isn't strict nor at compile time nor at runtime) but from a
practical standpoint it is safer.
If anybody really wants THP to run without compaction, it'd be such a
weird setup that editing the Kconfig file to allow it will be surely not a
problem.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:07 +0000 (15:47 -0800)]
thp: transparent hugepage config choice
Allow to choose between the always|madvise default for page faults and
khugepaged at config time. madvise guarantees zero risk of higher memory
footprint for applications (applications using madvise(MADV_HUGEPAGE)
won't risk to use any more memory by backing their virtual regions with
hugepages).
Initially set the default to N and don't depend on EMBEDDED.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:06 +0000 (15:47 -0800)]
thp: allocate memory in khugepaged outside of mmap_sem write mode
This tries to be more friendly to filesystem in userland, with userland
backends that allocate memory in the I/O paths and that could deadlock if
khugepaged holds the mmap_sem write mode of the userland backend while
allocating memory. Memory allocation may wait for writeback I/O
completion from the daemon that may be blocked in the mmap_sem read mode
if a page fault happens and the daemon wasn't using mlock for the memory
required for the I/O submission and completion.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:05 +0000 (15:47 -0800)]
thp: add numa awareness to hugepage allocations
It's mostly a matter of replacing alloc_pages with alloc_pages_vma after
introducing alloc_pages_vma. khugepaged needs special handling as the
allocation has to happen inside collapse_huge_page where the vma is known
and an error has to be returned to the outer loop to sleep
alloc_sleep_millisecs in case of failure. But it retains the more
efficient logic of handling allocation failures in khugepaged in case of
CONFIG_NUMA=n.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:05 +0000 (15:47 -0800)]
thp: enable direct defrag
With memory compaction in, and lumpy-reclaim disabled, it seems safe
enough to defrag memory during the (synchronous) transparent hugepage page
faults (TRANSPARENT_HUGEPAGE_DEFRAG_FLAG) and not only during khugepaged
(async) hugepage allocations that was already enabled even before memory
compaction was in (TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG).
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:47:00 +0000 (15:47 -0800)]
thp: remove PG_buddy
PG_buddy can be converted to _mapcount == -2. So the PG_compound_lock can
be added to page->flags without overflowing (because of the sparse section
bits increasing) with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y. This also
has to move the memory hotplug code from _mapcount to lru.next to avoid
any risk of clashes. We can't use lru.next for PG_buddy removal, but
memory hotplug can use lru.next even more easily than the mapcount
instead.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:58 +0000 (15:46 -0800)]
thp: khugepaged
Add khugepaged to relocate fragmented pages into hugepages if new
hugepages become available. (this is indipendent of the defrag logic that
will have to make new hugepages available)
The fundamental reason why khugepaged is unavoidable, is that some memory
can be fragmented and not everything can be relocated. So when a virtual
machine quits and releases gigabytes of hugepages, we want to use those
freely available hugepages to create huge-pmd in the other virtual
machines that may be running on fragmented memory, to maximize the CPU
efficiency at all times. The scan is slow, it takes nearly zero cpu time,
except when it copies data (in which case it means we definitely want to
pay for that cpu time) so it seems a good tradeoff.
In addition to the hugepages being released by other process releasing
memory, we have the strong suspicion that the performance impact of
potentially defragmenting hugepages during or before each page fault could
lead to more performance inconsistency than allocating small pages at
first and having them collapsed into large pages later... if they prove
themselfs to be long lived mappings (khugepaged scan is slow so short
lived mappings have low probability to run into khugepaged if compared to
long lived mappings).
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
By this patch, when a transparent hugepage is charged, not only the head
page but also all the tail pages are committed, IOW pc->mem_cgroup and
pc->flags of tail pages are set.
Without this patch:
- Tail pages are not linked to any memcg's LRU at splitting. This causes many
problems, for example, the charged memcg's directory can never be rmdir'ed
because it doesn't have enough pages to scan to make the usage decrease to 0.
- "rss" field in memory.stat would be incorrect. Moreover, usage_in_bytes in
root cgroup is calculated by the stat not by res_counter(since 2.6.32),
it would be incorrect too.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:55 +0000 (15:46 -0800)]
thp: madvise(MADV_HUGEPAGE)
Add madvise MADV_HUGEPAGE to mark regions that are important to be
hugepage backed. Return -EINVAL if the vma is not of an anonymous type,
or the feature isn't built into the kernel. Never silently return
success.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:53 +0000 (15:46 -0800)]
thp: split_huge_page anon_vma ordering dependency
This documents how split_huge_page is safe vs new vma inserctions into the
anon_vma that may have already released the anon_vma->lock but not
established pmds yet when split_huge_page starts.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Hugh Dickins [Thu, 13 Jan 2011 23:46:52 +0000 (15:46 -0800)]
thp: transparent hugepage core fixlet
If you configure THP in addition to HUGETLB_PAGE on x86_32 without PAE,
the p?d-folding works out that munlock_vma_pages_range() can crash to
follow_page()'s pud_huge() BUG_ON(flags & FOLL_GET): it needs the same
VM_HUGETLB check already there on the pmd_huge() line. Conveniently,
openSUSE provides a "blogd" which tests this out at startup!
Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:52 +0000 (15:46 -0800)]
thp: transparent hugepage core
Lately I've been working to make KVM use hugepages transparently without
the usual restrictions of hugetlbfs. Some of the restrictions I'd like to
see removed:
1) hugepages have to be swappable or the guest physical memory remains
locked in RAM and can't be paged out to swap
2) if a hugepage allocation fails, regular pages should be allocated
instead and mixed in the same vma without any failure and without
userland noticing
3) if some task quits and more hugepages become available in the
buddy, guest physical memory backed by regular pages should be
relocated on hugepages automatically in regions under
madvise(MADV_HUGEPAGE) (ideally event driven by waking up the
kernel deamon if the order=HPAGE_PMD_SHIFT-PAGE_SHIFT list becomes
not null)
4) avoidance of reservation and maximization of use of hugepages whenever
possible. Reservation (needed to avoid runtime fatal faliures) may be ok for
1 machine with 1 database with 1 database cache with 1 database cache size
known at boot time. It's definitely not feasible with a virtualization
hypervisor usage like RHEV-H that runs an unknown number of virtual machines
with an unknown size of each virtual machine with an unknown amount of
pagecache that could be potentially useful in the host for guest not using
O_DIRECT (aka cache=off).
hugepages in the virtualization hypervisor (and also in the guest!) are
much more important than in a regular host not using virtualization,
becasue with NPT/EPT they decrease the tlb-miss cacheline accesses from 24
to 19 in case only the hypervisor uses transparent hugepages, and they
decrease the tlb-miss cacheline accesses from 19 to 15 in case both the
linux hypervisor and the linux guest both uses this patch (though the
guest will limit the addition speedup to anonymous regions only for
now...). Even more important is that the tlb miss handler is much slower
on a NPT/EPT guest than for a regular shadow paging or no-virtualization
scenario. So maximizing the amount of virtual memory cached by the TLB
pays off significantly more with NPT/EPT than without (even if there would
be no significant speedup in the tlb-miss runtime).
The first (and more tedious) part of this work requires allowing the VM to
handle anonymous hugepages mixed with regular pages transparently on
regular anonymous vmas. This is what this patch tries to achieve in the
least intrusive possible way. We want hugepages and hugetlb to be used in
a way so that all applications can benefit without changes (as usual we
leverage the KVM virtualization design: by improving the Linux VM at
large, KVM gets the performance boost too).
The most important design choice is: always fallback to 4k allocation if
the hugepage allocation fails! This is the _very_ opposite of some large
pagecache patches that failed with -EIO back then if a 64k (or similar)
allocation failed...
Second important decision (to reduce the impact of the feature on the
existing pagetable handling code) is that at any time we can split an
hugepage into 512 regular pages and it has to be done with an operation
that can't fail. This way the reliability of the swapping isn't decreased
(no need to allocate memory when we are short on memory to swap) and it's
trivial to plug a split_huge_page* one-liner where needed without
polluting the VM. Over time we can teach mprotect, mremap and friends to
handle pmd_trans_huge natively without calling split_huge_page*. The fact
it can't fail isn't just for swap: if split_huge_page would return -ENOMEM
(instead of the current void) we'd need to rollback the mprotect from the
middle of it (ideally including undoing the split_vma) which would be a
big change and in the very wrong direction (it'd likely be simpler not to
call split_huge_page at all and to teach mprotect and friends to handle
hugepages instead of rolling them back from the middle). In short the
very value of split_huge_page is that it can't fail.
The collapsing and madvise(MADV_HUGEPAGE) part will remain separated and
incremental and it'll just be an "harmless" addition later if this initial
part is agreed upon. It also should be noted that locking-wise replacing
regular pages with hugepages is going to be very easy if compared to what
I'm doing below in split_huge_page, as it will only happen when
page_count(page) matches page_mapcount(page) if we can take the PG_lock
and mmap_sem in write mode. collapse_huge_page will be a "best effort"
that (unlike split_huge_page) can fail at the minimal sign of trouble and
we can try again later. collapse_huge_page will be similar to how KSM
works and the madvise(MADV_HUGEPAGE) will work similar to
madvise(MADV_MERGEABLE).
The default I like is that transparent hugepages are used at page fault
time. This can be changed with
/sys/kernel/mm/transparent_hugepage/enabled. The control knob can be set
to three values "always", "madvise", "never" which mean respectively that
hugepages are always used, or only inside madvise(MADV_HUGEPAGE) regions,
or never used. /sys/kernel/mm/transparent_hugepage/defrag instead
controls if the hugepage allocation should defrag memory aggressively
"always", only inside "madvise" regions, or "never".
The pmd_trans_splitting/pmd_trans_huge locking is very solid. The
put_page (from get_user_page users that can't use mmu notifier like
O_DIRECT) that runs against a __split_huge_page_refcount instead was a
pain to serialize in a way that would result always in a coherent page
count for both tail and head. I think my locking solution with a
compound_lock taken only after the page_first is valid and is still a
PageHead should be safe but it surely needs review from SMP race point of
view. In short there is no current existing way to serialize the O_DIRECT
final put_page against split_huge_page_refcount so I had to invent a new
one (O_DIRECT loses knowledge on the mapping status by the time gup_fast
returns so...). And I didn't want to impact all gup/gup_fast users for
now, maybe if we change the gup interface substantially we can avoid this
locking, I admit I didn't think too much about it because changing the gup
unpinning interface would be invasive.
If we ignored O_DIRECT we could stick to the existing compound refcounting
code, by simply adding a get_user_pages_fast_flags(foll_flags) where KVM
(and any other mmu notifier user) would call it without FOLL_GET (and if
FOLL_GET isn't set we'd just BUG_ON if nobody registered itself in the
current task mmu notifier list yet). But O_DIRECT is fundamental for
decent performance of virtualized I/O on fast storage so we can't avoid it
to solve the race of put_page against split_huge_page_refcount to achieve
a complete hugepage feature for KVM.
Swap and oom works fine (well just like with regular pages ;). MMU
notifier is handled transparently too, with the exception of the young bit
on the pmd, that didn't have a range check but I think KVM will be fine
because the whole point of hugepages is that EPT/NPT will also use a huge
pmd when they notice gup returns pages with PageCompound set, so they
won't care of a range and there's just the pmd young bit to check in that
case.
NOTE: in some cases if the L2 cache is small, this may slowdown and waste
memory during COWs because 4M of memory are accessed in a single fault
instead of 8k (the payoff is that after COW the program can run faster).
So we might want to switch the copy_huge_page (and clear_huge_page too) to
not temporal stores. I also extensively researched ways to avoid this
cache trashing with a full prefault logic that would cow in 8k/16k/32k/64k
up to 1M (I can send those patches that fully implemented prefault) but I
concluded they're not worth it and they add an huge additional complexity
and they remove all tlb benefits until the full hugepage has been faulted
in, to save a little bit of memory and some cache during app startup, but
they still don't improve substantially the cache-trashing during startup
if the prefault happens in >4k chunks. One reason is that those 4k pte
entries copied are still mapped on a perfectly cache-colored hugepage, so
the trashing is the worst one can generate in those copies (cow of 4k page
copies aren't so well colored so they trashes less, but again this results
in software running faster after the page fault). Those prefault patches
allowed things like a pte where post-cow pages were local 4k regular anon
pages and the not-yet-cowed pte entries were pointing in the middle of
some hugepage mapped read-only. If it doesn't payoff substantially with
todays hardware it will payoff even less in the future with larger l2
caches, and the prefault logic would blot the VM a lot. If one is
emebdded transparent_hugepage can be disabled during boot with sysfs or
with the boot commandline parameter transparent_hugepage=0 (or
transparent_hugepage=2 to restrict hugepages inside madvise regions) that
will ensure not a single hugepage is allocated at boot time. It is simple
enough to just disable transparent hugepage globally and let transparent
hugepages be allocated selectively by applications in the MADV_HUGEPAGE
region (both at page fault time, and if enabled with the
collapse_huge_page too through the kernel daemon).
This patch supports only hugepages mapped in the pmd, archs that have
smaller hugepages will not fit in this patch alone. Also some archs like
power have certain tlb limits that prevents mixing different page size in
the same regions so they will not fit in this framework that requires
"graceful fallback" to basic PAGE_SIZE in case of physical memory
fragmentation. hugetlbfs remains a perfect fit for those because its
software limits happen to match the hardware limits. hugetlbfs also
remains a perfect fit for hugepage sizes like 1GByte that cannot be hoped
to be found not fragmented after a certain system uptime and that would be
very expensive to defragment with relocation, so requiring reservation.
hugetlbfs is the "reservation way", the point of transparent hugepages is
not to have any reservation at all and maximizing the use of cache and
hugepages at all times automatically.
Some performance result:
vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largep
ages3
memset page fault 1566023
memset tlb miss 453854
memset second tlb miss 453321
random access tlb miss 41635
random access second tlb miss 41658
vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largepages3
memset page fault 1566471
memset tlb miss 453375
memset second tlb miss 453320
random access tlb miss 41636
random access second tlb miss 41637
vmx andrea # ./largepages3
memset page fault 1566642
memset tlb miss 453417
memset second tlb miss 453313
random access tlb miss 41630
random access second tlb miss 41647
vmx andrea # ./largepages3
memset page fault 1566872
memset tlb miss 453418
memset second tlb miss 453315
random access tlb miss 41618
random access second tlb miss 41659
vmx andrea # echo 0 > /proc/sys/vm/transparent_hugepage
vmx andrea # ./largepages3
memset page fault 2182476
memset tlb miss 460305
memset second tlb miss 460179
random access tlb miss 44483
random access second tlb miss 44186
vmx andrea # ./largepages3
memset page fault 2182791
memset tlb miss 460742
memset second tlb miss 459962
random access tlb miss 43981
random access second tlb miss 43988
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:49 +0000 (15:46 -0800)]
thp: don't alloc harder for gfp nomemalloc even if nowait
Not worth throwing away the precious reserved free memory pool for
allocations that can fail gracefully (either through mempool or because
they're transhuge allocations later falling back to 4k allocations).
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:49 +0000 (15:46 -0800)]
thp: _GFP_NO_KSWAPD
Transparent hugepage allocations must be allowed not to invoke kswapd or
any other kind of indirect reclaim (especially when the defrag sysfs is
control disabled). It's unacceptable to swap out anonymous pages
(potentially anonymous transparent hugepages) in order to create new
transparent hugepages. This is true for the MADV_HUGEPAGE areas too
(swapping out a kvm virtual machine and so having it suffer an unbearable
slowdown, so another one with guest physical memory marked MADV_HUGEPAGE
can run 30% faster if it is running memory intensive workloads, makes no
sense). If a transparent hugepage allocation fails the slowdown is minor
and there is total fallback, so kswapd should never be asked to swapout
memory to allow the high order allocation to succeed.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:47 +0000 (15:46 -0800)]
thp: split_huge_page paging
Paging logic that splits the page before it is unmapped and added to swap
to ensure backwards compatibility with the legacy swap code. Eventually
swap should natively pageout the hugepages to increase performance and
decrease seeking and fragmentation of swap space. swapoff can just skip
over huge pmd as they cannot be part of swap yet. In add_to_swap be
careful to split the page only if we got a valid swap entry so we don't
split hugepages with a full swap.
In theory we could split pages before isolating them during the lru scan,
but for khugepaged to be safe, I'm relying on either mmap_sem write mode,
or PG_lock taken, so split_huge_page has to run either with mmap_sem
read/write mode or PG_lock taken. Calling it from isolate_lru_page would
make locking more complicated, in addition to that split_huge_page would
deadlock if called by __isolate_lru_page because it has to take the lru
lock to add the tail pages.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:46 +0000 (15:46 -0800)]
thp: split_huge_page_mm/vma
split_huge_page_pmd compat code. Each one of those would need to be
expanded to hundred of lines of complex code without a fully reliable
split_huge_page_pmd design.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:45 +0000 (15:46 -0800)]
thp: add pmd_huge_pte to mm_struct
This increase the size of the mm struct a bit but it is needed to
preallocate one pte for each hugepage so that split_huge_page will not
require a fail path. Guarantee of success is a fundamental property of
split_huge_page to avoid decrasing swapping reliability and to avoid
adding -ENOMEM fail paths that would otherwise force the hugepage-unaware
VM code to learn rolling back in the middle of its pte mangling operations
(if something we need it to learn handling pmd_trans_huge natively rather
being capable of rollback). When split_huge_page runs a pte is needed to
succeed the split, to map the newly splitted regular pages with a regular
pte. This way all existing VM code remains backwards compatible by just
adding a split_huge_page* one liner. The memory waste of those
preallocated ptes is negligible and so it is worth it.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:43 +0000 (15:46 -0800)]
thp: pte alloc trans splitting
pte alloc routines must wait for split_huge_page if the pmd is not present
and not null (i.e. pmd_trans_splitting). The additional branches are
optimized away at compile time by pmd_trans_splitting if the config option
is off. However we must pass the vma down in order to know the anon_vma
lock to wait for.
[akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:41 +0000 (15:46 -0800)]
thp: add pmd mangling functions to x86
Add needed pmd mangling functions with symmetry with their pte
counterparts. pmdp_splitting_flush() is the only new addition on the pmd_
methods and it's needed to serialize the VM against split_huge_page. It
simply atomically sets the splitting bit in a similar way
pmdp_clear_flush_young atomically clears the accessed bit.
pmdp_splitting_flush() also has to flush the tlb to make it effective
against gup_fast, but it wouldn't really require to flush the tlb too.
Just the tlb flush is the simplest operation we can invoke to serialize
pmdp_splitting_flush() against gup_fast.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrea Arcangeli [Thu, 13 Jan 2011 23:46:40 +0000 (15:46 -0800)]
thp: special pmd_trans_* functions
These returns 0 at compile time when the config option is disabled, to
allow gcc to eliminate the transparent hugepage function calls at compile
time without additional #ifdefs (only the export of those functions have
to be visible to gcc but they won't be required at link time and
huge_memory.o can be not built at all).
_PAGE_BIT_UNUSED1 is never used for pmd, only on pte.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>