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btrfs: split remaining space to discard in chunks

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commit a99fcb0158978ed332009449b484e5f3ca2d7df4 upstream.

Per Qu Wenruo in case we have a very large disk, e.g. 8TiB device,
mostly empty although we will do the split according to our super block
locations, the last super block ends at 256G, we can submit a huge
discard for the range [256G, 8T), causing a large delay.

Split the space left to discard based on BTRFS_MAX_DISCARD_CHUNK_SIZE in
preparation of introduction of cancellation points to trim. The value
of the chunk size is arbitrary, it can be higher or derived from actual
device capabilities but we can't easily read that using
bio_discard_limit().

Link: https://bugzilla.kernel.org/show_bug.cgi?id=219180
Link: https://bugzilla.suse.com/show_bug.cgi?id=1229737
CC: stable@vger.kernel.org # 5.15+
Signed-off-by: Luca Stefani <luca.stefani.ge1@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Luca Stefani 2024-09-17 22:33:04 +02:00 • committed by Greg Kroah-Hartman
parent 73a4f5a704
commit f00545e838
2 changed files with 21 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

19
fs/btrfs/extent-tree.c
View file

@ -1303,13 +1303,24 @@ static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
bytes_left = end - start;
}
if (bytes_left) {
while (bytes_left) {
u64 bytes_to_discard = min(BTRFS_MAX_DISCARD_CHUNK_SIZE, bytes_left);
ret = blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
bytes_left >> SECTOR_SHIFT,
bytes_to_discard >> SECTOR_SHIFT,
GFP_NOFS);
if (!ret)
*discarded_bytes += bytes_left;
if (ret) {
if (ret != -EOPNOTSUPP)
break;
continue;
}
start += bytes_to_discard;
bytes_left -= bytes_to_discard;
*discarded_bytes += bytes_to_discard;
}
return ret;
}

6
fs/btrfs/volumes.h
View file

@ -15,6 +15,12 @@
#define BTRFS_MAX_DATA_CHUNK_SIZE (10ULL * SZ_1G)
/*
* Arbitratry maximum size of one discard request to limit potentially long time
* spent in blkdev_issue_discard().
*/
#define BTRFS_MAX_DISCARD_CHUNK_SIZE (SZ_1G)
extern struct mutex uuid_mutex;
#define BTRFS_STRIPE_LEN SZ_64K