ext4: use non-movable memory for superblock readahead

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>

diff --git a/fs/buffer.c b/fs/buffer.c
index f73276d..599a0bf 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -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

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 68f6c0a..2a4aae6 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4364,7 +4364,7 @@ make_io:
                        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 9728e7b..83413f0 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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++) {

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index e0b020e..15b765a 100644 (file)
--- 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)
 {