Patchwork [4/6] block: Optionally snapshot page contents to provide stable pages during write

login
register
mail settings
Submitter Darrick J. Wong
Date Jan. 19, 2013, 1:13 a.m.
Message ID <20130119011301.20902.41628.stgit@blackbox.djwong.org>
Download mbox | patch
Permalink /patch/213764/
State Not Applicable
Headers show

Comments

Darrick J. Wong - Jan. 19, 2013, 1:13 a.m.
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.

Tested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 arch/tile/Kconfig       |    6 ------
 block/blk-core.c        |    8 +++++---
 fs/ext3/super.c         |    1 +
 include/uapi/linux/fs.h |    3 +++
 mm/Kconfig              |   13 +++++++++++++
 mm/bounce.c             |   48 +++++++++++++++++++++++++++++++++++++++++++----
 mm/page-writeback.c     |    4 ++++
 7 files changed, 70 insertions(+), 13 deletions(-)



--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Jan Kara - Jan. 21, 2013, 2:12 p.m.
On Fri 18-01-13 17:13:01, Darrick J. Wong wrote:
> 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.
> 
> Tested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  arch/tile/Kconfig       |    6 ------
>  block/blk-core.c        |    8 +++++---
>  fs/ext3/super.c         |    1 +
>  include/uapi/linux/fs.h |    3 +++
>  mm/Kconfig              |   13 +++++++++++++
>  mm/bounce.c             |   48 +++++++++++++++++++++++++++++++++++++++++++----
>  mm/page-writeback.c     |    4 ++++
>  7 files changed, 70 insertions(+), 13 deletions(-)
> 
> 
> diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
> index 875d008..c671fda 100644
> --- a/arch/tile/Kconfig
> +++ b/arch/tile/Kconfig
> @@ -410,12 +410,6 @@ 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 c973249..277134c 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1474,6 +1474,11 @@ 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;
> @@ -1714,9 +1719,6 @@ 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 6e50223..4ba2683 100644
> --- a/fs/ext3/super.c
> +++ b/fs/ext3/super.c
> @@ -2065,6 +2065,7 @@ 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 780d4c6..c7fc1e6 100644
> --- 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 278e3ab..7901d83 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -258,6 +258,19 @@ 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 0420867..5f89017 100644
> --- 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 9c5af4d..75a13f3 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2305,6 +2305,10 @@ 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);
>  }
>

Patch

diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
index 875d008..c671fda 100644
--- a/arch/tile/Kconfig
+++ b/arch/tile/Kconfig
@@ -410,12 +410,6 @@  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 c973249..277134c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1474,6 +1474,11 @@  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;
@@ -1714,9 +1719,6 @@  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 6e50223..4ba2683 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -2065,6 +2065,7 @@  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 780d4c6..c7fc1e6 100644
--- 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 278e3ab..7901d83 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -258,6 +258,19 @@  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 0420867..5f89017 100644
--- 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 9c5af4d..75a13f3 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2305,6 +2305,10 @@  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);
 }