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xfs: add lockless xfs_buf_readahead_map fast path

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Readahead currently always locks the buffer, which can cause contention
with actual users of the buffer.  Add a fast path without taking any
locks if the buffer is uptodate and not stale.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Christoph Hellwig 2026-07-15 16:51:05 +02:00 committed by Carlos Maiolino
parent 2aedf844be
commit 00f40876f4
1 changed files with 13 additions and 3 deletions
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16
fs/xfs/xfs_buf.c
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@ -756,13 +756,23 @@ xfs_buf_readahead_map(
if (xfs_find_get_buf(target, map, nmaps, flags, &bp))
return;
if (xfs_buf_find_lock(bp, XBF_TRYLOCK))
/*
* Do a lockless fast path check for a valid uptodate buffer and avoid
* locking entirely in this case.
*/
if ((READ_ONCE(bp->b_flags) & (XBF_DONE | XBF_STALE)) == XBF_DONE)
goto out_rele;
trace_xfs_buf_readahead(bp, 0, _RET_IP_);
if (bp->b_flags & XBF_DONE)
/* Otherwise lock the buffer to stabilize the state */
if (!xfs_buf_trylock(bp))
goto out_rele;
/* Let the actual reader deal with stale buffers. */
if (bp->b_flags & (XBF_STALE | XBF_DONE))
goto out_unlock;
trace_xfs_buf_readahead(bp, 0, _RET_IP_);
XFS_STATS_INC(target->bt_mount, xb_get_read);
bp->b_ops = ops;
xfs_buf_clear_flags(bp, XBF_WRITE | XBF_DONE);