[PATCH v2] ext4: use non-movable memory for superblock readahead

[PATCH v2] ext4: use non-movable memory for superblock readahead

[Roman Gushchin]

Since commit a8ac900b8163 ("ext4: use non-movable memory for the
superblock") buffers for ext4 superblock were allocated using
the sb_bread_unmovable() helper which allocated buffer heads
out of non-movable memory blocks. It was necessarily to not block
page migrations and do not cause cma allocation failures.

However commit 85c8f176a611 ("ext4: preload block group descriptors")
broke this by introducing pre-reading of the ext4 superblock.
The problem is that __breadahead() is using __getblk() underneath,
which allocates buffer heads out of movable memory.

It resulted in page migration failures I've seen on a machine
with an ext4 partition and a preallocated cma area.

Fix this by introducing sb_breadahead_unmovable() and
__breadahead_gfp() helpers which use non-movable memory for buffer
head allocations and use them for the ext4 superblock readahead.

v2: found a similar issue in __ext4_get_inode_loc()

Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Andrew Perepechko <andrew.perepechko@seagate.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Gioh Kim <gioh.kim@lge.com>
Cc: Jan Kara <jack@suse.cz>
---
 fs/buffer.c                 | 11 +++++++++++
 fs/ext4/inode.c             |  2 +-
 fs/ext4/super.c             |  2 +-
 include/linux/buffer_head.h |  8 ++++++++
 4 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 4299e100a05b..25462edd920e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1414,6 +1414,17 @@ void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
 }
 EXPORT_SYMBOL(__breadahead);
 
+void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
+		      gfp_t gfp)
+{
+	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
+	if (likely(bh)) {
+		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
+		brelse(bh);
+	}
+}
+EXPORT_SYMBOL(__breadahead_gfp);
+
 /**
  *  __bread_gfp() - reads a specified block and returns the bh
  *  @bdev: the block_device to read from
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fa0ff78dc033..b131fedc6b77 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4348,7 +4348,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
 			if (end > table)
 				end = table;
 			while (b <= end)
-				sb_breadahead(sb, b++);
+				sb_breadahead_unmovable(sb, b++);
 		}
 
 		/*
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ff1b764b0c0e..fb2338a5220e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4331,7 +4331,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	/* Pre-read the descriptors into the buffer cache */
 	for (i = 0; i < db_count; i++) {
 		block = descriptor_loc(sb, logical_sb_block, i);
-		sb_breadahead(sb, block);
+		sb_breadahead_unmovable(sb, block);
 	}
 
 	for (i = 0; i < db_count; i++) {
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 7b73ef7f902d..b56cc825f64d 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -189,6 +189,8 @@ struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
 void __brelse(struct buffer_head *);
 void __bforget(struct buffer_head *);
 void __breadahead(struct block_device *, sector_t block, unsigned int size);
+void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
+		  gfp_t gfp);
 struct buffer_head *__bread_gfp(struct block_device *,
 				sector_t block, unsigned size, gfp_t gfp);
 void invalidate_bh_lrus(void);
@@ -319,6 +321,12 @@ sb_breadahead(struct super_block *sb, sector_t block)
 	__breadahead(sb->s_bdev, block, sb->s_blocksize);
 }
 
+static inline void
+sb_breadahead_unmovable(struct super_block *sb, sector_t block)
+{
+	__breadahead_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
+}
+
 static inline struct buffer_head *
 sb_getblk(struct super_block *sb, sector_t block)
 {
-- 
2.24.1

Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Andreas Dilger]

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On Feb 28, 2020, at 5:14 PM, Roman Gushchin <guro@fb.com> wrote:
> 
> Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> superblock") buffers for ext4 superblock were allocated using
> the sb_bread_unmovable() helper which allocated buffer heads
> out of non-movable memory blocks. It was necessarily to not block
> page migrations and do not cause cma allocation failures.
> 
> However commit 85c8f176a611 ("ext4: preload block group descriptors")
> broke this by introducing pre-reading of the ext4 superblock.
> The problem is that __breadahead() is using __getblk() underneath,
> which allocates buffer heads out of movable memory.
> 
> It resulted in page migration failures I've seen on a machine
> with an ext4 partition and a preallocated cma area.
> 
> Fix this by introducing sb_breadahead_unmovable() and
> __breadahead_gfp() helpers which use non-movable memory for buffer
> head allocations and use them for the ext4 superblock readahead.
> 
> v2: found a similar issue in __ext4_get_inode_loc()
> 
> Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> Cc: Andrew Perepechko <andrew.perepechko@seagate.com>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Gioh Kim <gioh.kim@lge.com>
> Cc: Jan Kara <jack@suse.cz>
> ---
> fs/buffer.c                 | 11 +++++++++++
> fs/ext4/inode.c             |  2 +-
> fs/ext4/super.c             |  2 +-
> include/linux/buffer_head.h |  8 ++++++++
> 4 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 4299e100a05b..25462edd920e 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1414,6 +1414,17 @@ void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
> }
> EXPORT_SYMBOL(__breadahead);
> 
> +void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
> +		      gfp_t gfp)
> +{
> +	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
> +	if (likely(bh)) {
> +		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
> +		brelse(bh);
> +	}
> +}
> +EXPORT_SYMBOL(__breadahead_gfp);
> +
> /**
>  *  __bread_gfp() - reads a specified block and returns the bh
>  *  @bdev: the block_device to read from
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fa0ff78dc033..b131fedc6b77 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4348,7 +4348,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
> 			if (end > table)
> 				end = table;
> 			while (b <= end)
> -				sb_breadahead(sb, b++);
> +				sb_breadahead_unmovable(sb, b++);
> 		}
> 
> 		/*
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ff1b764b0c0e..fb2338a5220e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4331,7 +4331,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> 	/* Pre-read the descriptors into the buffer cache */
> 	for (i = 0; i < db_count; i++) {
> 		block = descriptor_loc(sb, logical_sb_block, i);
> -		sb_breadahead(sb, block);
> +		sb_breadahead_unmovable(sb, block);
> 	}
> 
> 	for (i = 0; i < db_count; i++) {
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 7b73ef7f902d..b56cc825f64d 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -189,6 +189,8 @@ struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
> void __brelse(struct buffer_head *);
> void __bforget(struct buffer_head *);
> void __breadahead(struct block_device *, sector_t block, unsigned int size);
> +void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
> +		  gfp_t gfp);
> struct buffer_head *__bread_gfp(struct block_device *,
> 				sector_t block, unsigned size, gfp_t gfp);
> void invalidate_bh_lrus(void);
> @@ -319,6 +321,12 @@ sb_breadahead(struct super_block *sb, sector_t block)
> 	__breadahead(sb->s_bdev, block, sb->s_blocksize);
> }
> 
> +static inline void
> +sb_breadahead_unmovable(struct super_block *sb, sector_t block)
> +{
> +	__breadahead_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
> +}
> +
> static inline struct buffer_head *
> sb_getblk(struct super_block *sb, sector_t block)
> {
> --
> 2.24.1
> 


Cheers, Andreas






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Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Roman Gushchin]

On Sat, Feb 29, 2020 at 12:49:13AM -0700, Andreas Dilger wrote:
> On Feb 28, 2020, at 5:14 PM, Roman Gushchin <guro@fb.com> wrote:
> > 
> > Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> > superblock") buffers for ext4 superblock were allocated using
> > the sb_bread_unmovable() helper which allocated buffer heads
> > out of non-movable memory blocks. It was necessarily to not block
> > page migrations and do not cause cma allocation failures.
> > 
> > However commit 85c8f176a611 ("ext4: preload block group descriptors")
> > broke this by introducing pre-reading of the ext4 superblock.
> > The problem is that __breadahead() is using __getblk() underneath,
> > which allocates buffer heads out of movable memory.
> > 
> > It resulted in page migration failures I've seen on a machine
> > with an ext4 partition and a preallocated cma area.
> > 
> > Fix this by introducing sb_breadahead_unmovable() and
> > __breadahead_gfp() helpers which use non-movable memory for buffer
> > head allocations and use them for the ext4 superblock readahead.
> > 
> > v2: found a similar issue in __ext4_get_inode_loc()
> > 
> > Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> 
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Thank you!

Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Roman Gushchin]

On Sat, Feb 29, 2020 at 12:49:13AM -0700, Andreas Dilger wrote:
> On Feb 28, 2020, at 5:14 PM, Roman Gushchin <guro@fb.com> wrote:
> > 
> > Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> > superblock") buffers for ext4 superblock were allocated using
> > the sb_bread_unmovable() helper which allocated buffer heads
> > out of non-movable memory blocks. It was necessarily to not block
> > page migrations and do not cause cma allocation failures.
> > 
> > However commit 85c8f176a611 ("ext4: preload block group descriptors")
> > broke this by introducing pre-reading of the ext4 superblock.
> > The problem is that __breadahead() is using __getblk() underneath,
> > which allocates buffer heads out of movable memory.
> > 
> > It resulted in page migration failures I've seen on a machine
> > with an ext4 partition and a preallocated cma area.
> > 
> > Fix this by introducing sb_breadahead_unmovable() and
> > __breadahead_gfp() helpers which use non-movable memory for buffer
> > head allocations and use them for the ext4 superblock readahead.
> > 
> > v2: found a similar issue in __ext4_get_inode_loc()
> > 
> > Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> 
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Is it good to go?
Can it go through the ext4 tree?

Thanks!

Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Roman Gushchin]

On Sat, Feb 29, 2020 at 12:49:13AM -0700, Andreas Dilger wrote:
> On Feb 28, 2020, at 5:14 PM, Roman Gushchin <guro@fb.com> wrote:
> > 
> > Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> > superblock") buffers for ext4 superblock were allocated using
> > the sb_bread_unmovable() helper which allocated buffer heads
> > out of non-movable memory blocks. It was necessarily to not block
> > page migrations and do not cause cma allocation failures.
> > 
> > However commit 85c8f176a611 ("ext4: preload block group descriptors")
> > broke this by introducing pre-reading of the ext4 superblock.
> > The problem is that __breadahead() is using __getblk() underneath,
> > which allocates buffer heads out of movable memory.
> > 
> > It resulted in page migration failures I've seen on a machine
> > with an ext4 partition and a preallocated cma area.
> > 
> > Fix this by introducing sb_breadahead_unmovable() and
> > __breadahead_gfp() helpers which use non-movable memory for buffer
> > head allocations and use them for the ext4 superblock readahead.
> > 
> > v2: found a similar issue in __ext4_get_inode_loc()
> > 
> > Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> 
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Hello, Theodore!

Can you, please, pick this patch?

We've some changes on the mm side (more actively using a cma area for movable
allocations), which might bring a regression without this ext4 change.

Thank you!

Roman

Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Theodore Y. Ts'o]

On Fri, Feb 28, 2020 at 04:14:11PM -0800, Roman Gushchin wrote:
> Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> superblock") buffers for ext4 superblock were allocated using
> the sb_bread_unmovable() helper which allocated buffer heads
> out of non-movable memory blocks. It was necessarily to not block
> page migrations and do not cause cma allocation failures.
> 
> However commit 85c8f176a611 ("ext4: preload block group descriptors")
> broke this by introducing pre-reading of the ext4 superblock.
> The problem is that __breadahead() is using __getblk() underneath,
> which allocates buffer heads out of movable memory.
> 
> It resulted in page migration failures I've seen on a machine
> with an ext4 partition and a preallocated cma area.
> 
> Fix this by introducing sb_breadahead_unmovable() and
> __breadahead_gfp() helpers which use non-movable memory for buffer
> head allocations and use them for the ext4 superblock readahead.

Applied, thanks.  Apologies for not picking this up earlier.

	 	  	    	    	    - Ted

Re: [PATCH v2] ext4: use non-movable memory for superblock readahead

[Roman Gushchin]

On Thu, Apr 09, 2020 at 11:23:44PM -0400, Theodore Y. Ts'o wrote:
> On Fri, Feb 28, 2020 at 04:14:11PM -0800, Roman Gushchin wrote:
> > Since commit a8ac900b8163 ("ext4: use non-movable memory for the
> > superblock") buffers for ext4 superblock were allocated using
> > the sb_bread_unmovable() helper which allocated buffer heads
> > out of non-movable memory blocks. It was necessarily to not block
> > page migrations and do not cause cma allocation failures.
> > 
> > However commit 85c8f176a611 ("ext4: preload block group descriptors")
> > broke this by introducing pre-reading of the ext4 superblock.
> > The problem is that __breadahead() is using __getblk() underneath,
> > which allocates buffer heads out of movable memory.
> > 
> > It resulted in page migration failures I've seen on a machine
> > with an ext4 partition and a preallocated cma area.
> > 
> > Fix this by introducing sb_breadahead_unmovable() and
> > __breadahead_gfp() helpers which use non-movable memory for buffer
> > head allocations and use them for the ext4 superblock readahead.
> 
> Applied, thanks.  Apologies for not picking this up earlier.
> 
> 	 	  	    	    	    - Ted

Thank you!

Roman