[PATCH] improve shrink_dcache_sb()
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(n2) 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 <firstname.lastname@example.org>
Signed-off-by: Kirill Korotaev <email@example.com>
Signed-off-by: Andrey Mirkin <firstname.lastname@example.org>