xfs: implement lazy removal for the dquot freelist
Do not remove dquots from the freelist when we grab a reference to them in
xfs_qm_dqlookup, but leave them on the freelist util scanning notices that
they have a reference. This speeds up the lookup fastpath, and greatly
simplifies the lock ordering constraints. Note that the same scheme is
used by the VFS inode and dentry caches.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index be1df68..6a0c4f0 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -517,13 +517,12 @@
* get them off mplist and hashlist, but leave them on freelist.
*/
list_for_each_entry_safe(dqp, n, &q->qi_dqlist, q_mplist) {
- /*
- * It's OK to look at the type without taking dqlock here.
- * We're holding the mplist lock here, and that's needed for
- * a dqreclaim.
- */
- if ((dqp->dq_flags & dqtype) == 0)
+ xfs_dqlock(dqp);
+ if ((dqp->dq_flags & dqtype) == 0) {
+ xfs_dqunlock(dqp);
continue;
+ }
+ xfs_dqunlock(dqp);
if (!mutex_trylock(&dqp->q_hash->qh_lock)) {
nrecl = q->qi_dqreclaims;
@@ -1692,14 +1691,15 @@
xfs_dqlock(dqp);
/*
- * We are racing with dqlookup here. Naturally we don't
- * want to reclaim a dquot that lookup wants. We release the
- * freelist lock and start over, so that lookup will grab
- * both the dquot and the freelistlock.
+ * This dquot has already been grabbed by dqlookup.
+ * Remove it from the freelist and try again.
*/
- if (dqp->dq_flags & XFS_DQ_WANT) {
+ if (dqp->q_nrefs) {
trace_xfs_dqreclaim_want(dqp);
XQM_STATS_INC(xqmstats.xs_qm_dqwants);
+
+ list_del_init(&dqp->q_freelist);
+ xfs_Gqm->qm_dqfrlist_cnt--;
restarts++;
startagain = 1;
goto dqunlock;