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btrfs: avoid blocking when allocating context for nowait dio read/write 

When doing a NOWAIT direct IO read/write, we allocate a context object
(struct btrfs_dio_data) with GFP_NOFS, which can result in blocking
waiting for memory allocation (GFP_NOFS is __GFP_RECLAIM | __GFP_IO).
This is undesirable for the NOWAIT semantics, so do the allocation with
GFP_NOWAIT if we are serving a NOWAIT request and if the allocation fails
return -EAGAIN, so that the caller can fallback to a blocking context and
retry with a non-blocking write.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2022-03-23 16:19:29 +00:00 committed by David Sterba
parent 59d35c5171
commit 4f208dcc6b
1 changed files with 9 additions and 3 deletions
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6
fs/btrfs/inode.c
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@ -7588,9 +7588,15 @@ static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start,
}
}
if (flags & IOMAP_NOWAIT) {
dio_data = kzalloc(sizeof(*dio_data), GFP_NOWAIT);
if (!dio_data)
return -EAGAIN;
} else {
dio_data = kzalloc(sizeof(*dio_data), GFP_NOFS);
if (!dio_data)
return -ENOMEM;
}
iomap->private = dio_data;