Commit fbfdc9fc authored by NeilBrown's avatar NeilBrown Committed by Chuck Lever
Browse files

nfsd: filecache: drop the list_lru lock during lock gc scans 



Under a high NFSv3 load with lots of different files being accessed,
the LRU list of garbage-collectable files can become quite long.

Asking list_lru_scan_node() to scan the whole list can result in a long
period during which a spinlock is held, blocking the addition of new LRU
items.

So ask list_lru_scan_node() to scan only a few entries at a time, and
repeat until the scan is complete.

If the shrinker runs between two consecutive calls of
list_lru_scan_node() it could invalidate the "remaining" counter which
could lead to premature freeing.  So add a spinlock to avoid that.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
parent 56221b42

fs/nfsd/filecache.c

+24 −3
Original line number Diff line number Diff line
@@ -544,6 +544,13 @@ nfsd_file_gc_cb(struct list_head *item, struct list_lru_one *lru, 
	return nfsd_file_lru_cb(item, lru, arg);

}



/* If the shrinker runs between calls to list_lru_walk_node() in

 * nfsd_file_gc(), the "remaining" count will be wrong.  This could

 * result in premature freeing of some files.  This may not matter much

 * but is easy to fix with this spinlock which temporarily disables

 * the shrinker.

 */

static DEFINE_SPINLOCK(nfsd_gc_lock);

static void

nfsd_file_gc(void)

{
@@ -551,12 +558,22 @@ nfsd_file_gc(void) 
	LIST_HEAD(dispose);

	int nid;



	spin_lock(&nfsd_gc_lock);

	for_each_node_state(nid, N_NORMAL_MEMORY) {

		unsigned long nr = list_lru_count_node(&nfsd_file_lru, nid);

		unsigned long remaining = list_lru_count_node(&nfsd_file_lru, nid);



		while (remaining > 0) {

			unsigned long nr = min(remaining, NFSD_FILE_GC_BATCH);



			remaining -= nr;

			ret += list_lru_walk_node(&nfsd_file_lru, nid, nfsd_file_gc_cb,

						  &dispose, &nr);

			if (nr)

				/* walk aborted early */

				remaining = 0;

		}

	}

	spin_unlock(&nfsd_gc_lock);

	trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru));

	nfsd_file_dispose_list_delayed(&dispose);

}
@@ -581,8 +598,12 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc) 
	LIST_HEAD(dispose);

	unsigned long ret;



	if (!spin_trylock(&nfsd_gc_lock))

		return SHRINK_STOP;



	ret = list_lru_shrink_walk(&nfsd_file_lru, sc,

				   nfsd_file_lru_cb, &dispose);

	spin_unlock(&nfsd_gc_lock);

	trace_nfsd_file_shrinker_removed(ret, list_lru_count(&nfsd_file_lru));

	nfsd_file_dispose_list_delayed(&dispose);

	return ret;

fs/nfsd/filecache.h

+6 −0
Original line number Diff line number Diff line
@@ -3,6 +3,12 @@ 


#include <linux/fsnotify_backend.h>



/*

 * Limit the time that the list_lru_one lock is held during

 * an LRU scan.

 */

#define NFSD_FILE_GC_BATCH     (16UL)



/*

 * This is the fsnotify_mark container that nfsd attaches to the files that it

 * is holding open. Note that we have a separate refcount here aside from the