tree 53dcaad31bb6b74d1d37491b56450a675490b88b
parent 44a2db43eb715b54618bf01520cc5d46376cdbe2
author Denis V. Lunev <den@openvz.org> 1192602593 -0700
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1192635777 -0700

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: Denis V. Lunev <den@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Andrey Mirkin <amirkin@openvz.org>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>