[PATCH AUTOSEL 4.14 14/21] ext4: use non-movable memory for superblock readahead

Sasha Levin
2020-04-24T12:24:42Z

From: Roman Gushchin <guro@fb.com>

[ Upstream commit d87f639258a6a5980183f11876c884931ad93da2 ]

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.

Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Fixes: 85c8f176a611 ("ext4: preload block group descriptors")
Signed-off-by: Roman Gushchin <guro@fb.com>
Link: https://lore.kernel.org/r/20200229001411.128010-1-guro@fb.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 bdca7b10e239b..cae7f24a0410e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1398,6 +1398,17 @@ 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 10838b28c5bbd..c8a1c68c33ae5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4593,7 +4593,7 @@ 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 f5646bcad7702..074b9d43e24d8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4145,7 +4145,7 @@ 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 afa37f807f12c..2e1077ea77db0 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -187,6 +187,8 @@ 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)
{
--
2.20.1