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ext4: use non-movable memory for superblock readahead

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commit d87f639258a6a5980183f11876c884931ad93da2 upstream.

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 <[email protected]>
Fixes: 85c8f176a6 ("ext4: preload block group descriptors")
Signed-off-by: Roman Gushchin <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Roman Gushchin 2020-02-28 16:14:11 -08:00 • committed by Greg Kroah-Hartman
commit 41d097c833
4 changed files with 21 additions and 2 deletions
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2
fs/ext4/inode.c
View file

@ -4680,7 +4680,7 @@ 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

@ -4283,7 +4283,7 @@ 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++) {