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Commit 37c42524 authored by Denis V. Lunev's avatar Denis V. Lunev Committed by Linus Torvalds
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shrink_dcache_sb speedup



This patch makes shrink_dcache_sb consistent with dentry pruning policy.

On the first pass we iterate over dentry unused list and prepare some
dentries for removal.

However, since the existing code moves evicted dentries to the beginning of
the LRU it can happen that fresh dentries from other superblocks will be
inserted *before* our dentries.

This can result in significant slowdown of shrink_dcache_sb().  Moreover,
for virtual filesystems like unionfs which can call dput() during dentries
kill existing code results in O(n^2) complexity.

We observed 2 minutes shrink_dcache_sb() with only 35000 dentries.

To avoid this effects we propose to isolate sb dentries at the end
of LRU list.

Signed-off-by: default avatarDenis V. Lunev <den@openvz.org>
Signed-off-by: default avatarKirill Korotaev <dev@openvz.org>
Signed-off-by: default avatarAndrey Mirkin <amirkin@openvz.org>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 44a2db43
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