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xfs: remove a superflous hash lookup when inserting new buffers

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Currently on the slow path insert we repeat the initial hash table
lookup before we attempt the insert, resulting in a two traversals
of the hash table to ensure the insert is valid. The rhashtable API
provides a method for an atomic lookup and insert operation, so we
can avoid one of the hash table traversals by using this method.

Adapted from a large patch containing this optimisation by Christoph
Hellwig.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
This commit is contained in:
Dave Chinner 2022-07-14 12:04:43 +10:00 committed by Dave Chinner
parent d8d9bbb0ee
commit 32dd4f9c50
1 changed files with 9 additions and 4 deletions
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13
fs/xfs/xfs_buf.c
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@ -623,8 +623,15 @@ xfs_buf_find_insert(
}
spin_lock(&pag->pag_buf_lock);
bp = rhashtable_lookup(&pag->pag_buf_hash, cmap, xfs_buf_hash_params);
bp = rhashtable_lookup_get_insert_fast(&pag->pag_buf_hash,
&new_bp->b_rhash_head, xfs_buf_hash_params);
if (IS_ERR(bp)) {
error = PTR_ERR(bp);
spin_unlock(&pag->pag_buf_lock);
goto out_free_buf;
}
if (bp) {
/* found an existing buffer */
atomic_inc(&bp->b_hold);
spin_unlock(&pag->pag_buf_lock);
error = xfs_buf_find_lock(bp, flags);
@ -635,10 +642,8 @@ xfs_buf_find_insert(
goto out_free_buf;
}
/* The buffer keeps the perag reference until it is freed. */
/* The new buffer keeps the perag reference until it is freed. */
new_bp->b_pag = pag;
rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
xfs_buf_hash_params);
spin_unlock(&pag->pag_buf_lock);
*bpp = new_bp;
return 0;