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>

1 files changed, 11 insertions, 11 deletions

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index be1df6839237..6a0c4f0d9306 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -517,13 +517,12 @@ xfs_qm_dqpurge_int(
          * 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 @@ again:
                 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;