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ext4: use non-movable memory for superblock readahead 

Since commit a8ac900b81 ("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 85c8f176a6 ("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: 85c8f176a6 ("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>
This commit is contained in:
Roman Gushchin 2020-02-28 16:14:11 -08:00 committed by Theodore Ts'o
parent c2a559bc0e
commit d87f639258
4 changed files with 21 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/buffer.c
View File

@ -1371,6 +1371,17 @@ 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

2
fs/ext4/inode.c
View File

@ -4364,7 +4364,7 @@ make_io:
if (end > table)
end = table;
while (b <= end)
sb_breadahead(sb, b++);
sb_breadahead_unmovable(sb, b++);
}
/*

2
fs/ext4/super.c
View File

@ -4340,7 +4340,7 @@ 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++) {

8
include/linux/buffer_head.h
View File

@ -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)
{