Commit d87f6392 authored by Roman Gushchin's avatar Roman Gushchin Committed by Theodore Ts'o
Browse files

ext4: use non-movable memory for superblock readahead 



Since commit a8ac900b ("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 85c8f176 ("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: default avatarAndreas Dilger <adilger@dilger.ca>
Fixes: 85c8f176 ("ext4: preload block group descriptors")
Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Link: https://lore.kernel.org/r/20200229001411.128010-1-guro@fb.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent c2a559bc

fs/buffer.c

+11 −0
Original line number Diff line number Diff line
@@ -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

fs/ext4/inode.c

+1 −1
Original line number Diff line number Diff line
@@ -4364,7 +4364,7 @@ make_io: 
			if (end > table)

				end = table;

			while (b <= end)

				sb_breadahead(sb, b++);

				sb_breadahead_unmovable(sb, b++);

		}



		/*

fs/ext4/super.c

+1 −1
Original line number Diff line number Diff line
@@ -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++) {

include/linux/buffer_head.h

+8 −0
Original line number Diff line number Diff line
@@ -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)

{

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