block: optionally snapshot page contents to provide stable pages during write

This provides a band-aid to provide stable page writes on jbd without
needing to backport the fixed locking and page writeback bit handling
schemes of jbd2.  The band-aid works by using bounce buffers to snapshot
page contents instead of waiting.

For those wondering about the ext3 bandage -- fixing the jbd locking
(which was done as part of ext4dev years ago) is a lot of surgery, and
setting PG_writeback on data pages when we actually hold the page lock
dropped ext3 performance by nearly an order of magnitude.  If we're going
to migrate iscsi and raid to use stable page writes, the complaints about
high latency will likely return.  We might as well centralize their page
snapshotting thing to one place.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
index 59763412e4ddd7bbdcb90c5602876cf5e99224be..4d882dc209fac404ef99159fe00a35fa540eaefe 100644 (file)
--- a/arch/tile/Kconfig
+++ b/arch/tile/Kconfig
@@ -416,12 +416,6 @@ config TILE_USB
          Provides USB host adapter support for the built-in EHCI and OHCI
          interfaces on TILE-Gx chips.
 
-# USB OHCI needs the bounce pool since tilegx will often have more
-# than 4GB of memory, but we don't currently use the IOTLB to present
-# a 32-bit address to OHCI.  So we need to use a bounce pool instead.
-config NEED_BOUNCE_POOL
-       def_bool USB_OHCI_HCD
-
 source "drivers/pci/hotplug/Kconfig"
 
 endmenu

diff --git a/block/blk-core.c b/block/blk-core.c
index 66d31687cf6b4f47313c404f654dcda6a2017864..074b758efc42cf116d61f4755f0107f491890980 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1473,6 +1473,11 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
         */
        blk_queue_bounce(q, &bio);
 
+       if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
+               bio_endio(bio, -EIO);
+               return;
+       }
+
        if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
                spin_lock_irq(q->queue_lock);
                where = ELEVATOR_INSERT_FLUSH;
@@ -1706,9 +1711,6 @@ generic_make_request_checks(struct bio *bio)
         */
        blk_partition_remap(bio);
 
-       if (bio_integrity_enabled(bio) && bio_integrity_prep(bio))
-               goto end_io;
-
        if (bio_check_eod(bio, nr_sectors))
                goto end_io;
 

diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 0926fe46ae3e94aded3247f5bae817b834f253cb..5546ca225ffe19ee3e53d75ee4e18936fa47cc83 100644 (file)
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -2067,6 +2067,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
                test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ? "journal":
                test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA ? "ordered":
                "writeback");
+       sb->s_flags |= MS_SNAP_STABLE;
 
        return 0;
 

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 780d4c6093eb767ff7bd15ee30cd07bb76b04763..c7fc1e6517c3d21c5f9ad717ab36ed4956bfd0fe 100644 (file)
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -86,6 +86,9 @@ struct inodes_stat_t {
 #define MS_KERNMOUNT   (1<<22) /* this is a kern_mount call */
 #define MS_I_VERSION   (1<<23) /* Update inode I_version field */
 #define MS_STRICTATIME (1<<24) /* Always perform atime updates */
+
+/* These sb flags are internal to the kernel */
+#define MS_SNAP_STABLE (1<<27) /* Snapshot pages during writeback, if needed */
 #define MS_NOSEC       (1<<28)
 #define MS_BORN                (1<<29)
 #define MS_ACTIVE      (1<<30)

diff --git a/mm/Kconfig b/mm/Kconfig
index 850524e032d6df26ada17fe214af57172c68aed3..2c7aea7106f9816dc41184f01a2d367c81749a1d 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -266,6 +266,19 @@ config BOUNCE
        def_bool y
        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 
+# On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
+# have more than 4GB of memory, but we don't currently use the IOTLB to present
+# a 32-bit address to OHCI.  So we need to use a bounce pool instead.
+#
+# We also use the bounce pool to provide stable page writes for jbd.  jbd
+# initiates buffer writeback without locking the page or setting PG_writeback,
+# and fixing that behavior (a second time; jbd2 doesn't have this problem) is
+# a major rework effort.  Instead, use the bounce buffer to snapshot pages
+# (until jbd goes away).  The only jbd user is ext3.
+config NEED_BOUNCE_POOL
+       bool
+       default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD)
+
 config NR_QUICK
        int
        depends on QUICKLIST

diff --git a/mm/bounce.c b/mm/bounce.c
index 0420867755615d4f78be0272caf87e8d5b0fb112..5f89017686025f9201d62486bde9dbf078dc4423 100644 (file)
--- a/mm/bounce.c
+++ b/mm/bounce.c
@@ -178,8 +178,45 @@ static void bounce_end_io_read_isa(struct bio *bio, int err)
        __bounce_end_io_read(bio, isa_page_pool, err);
 }
 
+#ifdef CONFIG_NEED_BOUNCE_POOL
+static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
+{
+       struct page *page;
+       struct backing_dev_info *bdi;
+       struct address_space *mapping;
+       struct bio_vec *from;
+       int i;
+
+       if (bio_data_dir(bio) != WRITE)
+               return 0;
+
+       if (!bdi_cap_stable_pages_required(&q->backing_dev_info))
+               return 0;
+
+       /*
+        * Based on the first page that has a valid mapping, decide whether or
+        * not we have to employ bounce buffering to guarantee stable pages.
+        */
+       bio_for_each_segment(from, bio, i) {
+               page = from->bv_page;
+               mapping = page_mapping(page);
+               if (!mapping)
+                       continue;
+               bdi = mapping->backing_dev_info;
+               return mapping->host->i_sb->s_flags & MS_SNAP_STABLE;
+       }
+
+       return 0;
+}
+#else
+static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
+{
+       return 0;
+}
+#endif /* CONFIG_NEED_BOUNCE_POOL */
+
 static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
-                              mempool_t *pool)
+                              mempool_t *pool, int force)
 {
        struct page *page;
        struct bio *bio = NULL;
@@ -192,7 +229,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
                /*
                 * is destination page below bounce pfn?
                 */
-               if (page_to_pfn(page) <= queue_bounce_pfn(q))
+               if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
                        continue;
 
                /*
@@ -270,6 +307,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
 
 void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
 {
+       int must_bounce;
        mempool_t *pool;
 
        /*
@@ -278,13 +316,15 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
        if (!bio_has_data(*bio_orig))
                return;
 
+       must_bounce = must_snapshot_stable_pages(q, *bio_orig);
+
        /*
         * for non-isa bounce case, just check if the bounce pfn is equal
         * to or bigger than the highest pfn in the system -- in that case,
         * don't waste time iterating over bio segments
         */
        if (!(q->bounce_gfp & GFP_DMA)) {
-               if (queue_bounce_pfn(q) >= blk_max_pfn)
+               if (queue_bounce_pfn(q) >= blk_max_pfn && !must_bounce)
                        return;
                pool = page_pool;
        } else {
@@ -295,7 +335,7 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
        /*
         * slow path
         */
-       __blk_queue_bounce(q, bio_orig, pool);
+       __blk_queue_bounce(q, bio_orig, pool, must_bounce);
 }
 
 EXPORT_SYMBOL(blk_queue_bounce);

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4514ad7415c327bfbbe9837f3a7955291f3a172d..efe68148f621959beb28987dd9430fff289f583f 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2311,6 +2311,10 @@ void wait_for_stable_page(struct page *page)
 
        if (!bdi_cap_stable_pages_required(bdi))
                return;
+#ifdef CONFIG_NEED_BOUNCE_POOL
+       if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE)
+               return;
+#endif /* CONFIG_NEED_BOUNCE_POOL */
 
        wait_on_page_writeback(page);
 }