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btrfs: do not start readahead for csum tree when scrubbing non-data b…
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…lock groups

When scrubbing a stripe of a block group we always start readahead for the
checksums btree and wait for it to complete, however when the blockgroup is
not a data block group (or a mixed block group) it is a waste of time to do
it, since there are no checksums for metadata extents in that btree.

So skip that when the block group does not have the data flag set, saving
some time doing memory allocations, queueing a job in the readahead work
queue, waiting for it to complete and potentially avoiding some IO as well
(when csum tree extents are not in memory already).

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Filipe Manana authored and David Sterba committed Dec 8, 2020
1 parent a57ad68 commit a6889ca
Showing 1 changed file with 12 additions and 8 deletions.
20 changes: 12 additions & 8 deletions fs/btrfs/scrub.c
Original file line number Diff line number Diff line change
Expand Up @@ -3084,17 +3084,21 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
key_end.offset = (u64)-1;
reada1 = btrfs_reada_add(root, &key, &key_end);

key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
key.type = BTRFS_EXTENT_CSUM_KEY;
key.offset = logical;
key_end.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
key_end.type = BTRFS_EXTENT_CSUM_KEY;
key_end.offset = logic_end;
reada2 = btrfs_reada_add(csum_root, &key, &key_end);
if (cache->flags & BTRFS_BLOCK_GROUP_DATA) {
key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
key.type = BTRFS_EXTENT_CSUM_KEY;
key.offset = logical;
key_end.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
key_end.type = BTRFS_EXTENT_CSUM_KEY;
key_end.offset = logic_end;
reada2 = btrfs_reada_add(csum_root, &key, &key_end);
} else {
reada2 = NULL;
}

if (!IS_ERR(reada1))
btrfs_reada_wait(reada1);
if (!IS_ERR(reada2))
if (!IS_ERR_OR_NULL(reada2))
btrfs_reada_wait(reada2);


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