fix quadratic behavior of shrink_dcache_parent()
The time shrink_dcache_parent() takes, grows quadratically with the depth
of the tree under 'parent'. This starts to get noticable at about 10,000.
These kinds of depths don't occur normally, and filesystems which invoke
shrink_dcache_parent() via d_invalidate() seem to have other depth
dependent timings, so it's not even easy to expose this problem.
However with FUSE it's easy to create a deep tree and d_invalidate()
will also get called. This can make a syscall hang for a very long
time.
This is the original discovery of the problem by Russ Cox:
http://article.gmane.org/gmane.comp.file-systems.fuse.devel/3826
The following patch fixes the quadratic behavior, by optionally allowing
prune_dcache() to prune ancestors of a dentry in one go, instead of doing
it one at a time.
Common code in dput() and prune_one_dentry() is extracted into a new helper
function d_kill().
shrink_dcache_parent() as well as shrink_dcache_sb() are converted to use
the ancestry-pruner option. Only for shrink_dcache_memory() is this
behavior not desirable, so it keeps using the old algorithm.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Maneesh Soni <maneesh@in.ibm.com>
Acked-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed