xfs: use a normal shrinker for the dquot freelist

Stop reusing dquots from the freelist when allocating new ones directly, and
implement a shrinker that actually follows the specifications for the
interface.  The shrinker implementation is still highly suboptimal at this
point, but we can gradually work on it.

This also fixes an bug in the previous lock ordering, where we would take
the hash and dqlist locks inside of the freelist lock against the normal
lock ordering.  This is only solvable by introducing the dispose list,
and thus not when using direct reclaim of unused dquots for new allocations.

As a side-effect the quota upper bound and used to free ratio values in
/proc/fs/xfs/xqm are set to 0 as these values don't make any sense in the
new world order.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

(cherry picked from commit 04da0c8196ac0b12fb6b84f4b7a51ad2fa56d869)

1 files changed, 111 insertions, 180 deletions

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 1b2f5b37eac..c872feaf369 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -50,7 +50,6 @@
  */
 struct mutex	xfs_Gqm_lock;
 struct xfs_qm	*xfs_Gqm;
-uint		ndquot;
 
 kmem_zone_t	*qm_dqzone;
 kmem_zone_t	*qm_dqtrxzone;
@@ -93,7 +92,6 @@ xfs_Gqm_init(void)
 		goto out_free_udqhash;
 
 	hsize /= sizeof(xfs_dqhash_t);
-	ndquot = hsize << 8;
 
 	xqm = kmem_zalloc(sizeof(xfs_qm_t), KM_SLEEP);
 	xqm->qm_dqhashmask = hsize - 1;
@@ -137,7 +135,6 @@ xfs_Gqm_init(void)
 		xqm->qm_dqtrxzone = qm_dqtrxzone;
 
 	atomic_set(&xqm->qm_totaldquots, 0);
-	xqm->qm_dqfree_ratio = XFS_QM_DQFREE_RATIO;
 	xqm->qm_nrefs = 0;
 	return xqm;
 
@@ -1600,216 +1597,150 @@ xfs_qm_init_quotainos(
 	return 0;
 }
 
+STATIC void
+xfs_qm_dqfree_one(
+	struct xfs_dquot	*dqp)
+{
+	struct xfs_mount	*mp = dqp->q_mount;
+	struct xfs_quotainfo	*qi = mp->m_quotainfo;
 
+	mutex_lock(&dqp->q_hash->qh_lock);
+	list_del_init(&dqp->q_hashlist);
+	dqp->q_hash->qh_version++;
+	mutex_unlock(&dqp->q_hash->qh_lock);
 
-/*
- * Pop the least recently used dquot off the freelist and recycle it.
- */
-STATIC struct xfs_dquot *
-xfs_qm_dqreclaim_one(void)
+	mutex_lock(&qi->qi_dqlist_lock);
+	list_del_init(&dqp->q_mplist);
+	qi->qi_dquots--;
+	qi->qi_dqreclaims++;
+	mutex_unlock(&qi->qi_dqlist_lock);
+
+	xfs_qm_dqdestroy(dqp);
+}
+
+STATIC void
+xfs_qm_dqreclaim_one(
+	struct xfs_dquot	*dqp,
+	struct list_head	*dispose_list)
 {
-	struct xfs_dquot	*dqp;
-	int			restarts = 0;
+	struct xfs_mount	*mp = dqp->q_mount;
+	int			error;
 
-	mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
-restart:
-	list_for_each_entry(dqp, &xfs_Gqm->qm_dqfrlist, q_freelist) {
-		struct xfs_mount *mp = dqp->q_mount;
+	if (!xfs_dqlock_nowait(dqp))
+		goto out_busy;
 
-		if (!xfs_dqlock_nowait(dqp))
-			continue;
+	/*
+	 * This dquot has acquired a reference in the meantime remove it from
+	 * the freelist and try again.
+	 */
+	if (dqp->q_nrefs) {
+		xfs_dqunlock(dqp);
 
-		/*
-		 * This dquot has already been grabbed by dqlookup.
-		 * Remove it from the freelist and try again.
-		 */
-		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++;
-			goto dqunlock;
-		}
+		trace_xfs_dqreclaim_want(dqp);
+		XQM_STATS_INC(xqmstats.xs_qm_dqwants);
 
-		ASSERT(dqp->q_hash);
-		ASSERT(!list_empty(&dqp->q_mplist));
+		list_del_init(&dqp->q_freelist);
+		xfs_Gqm->qm_dqfrlist_cnt--;
+		return;
+	}
 
-		/*
-		 * Try to grab the flush lock. If this dquot is in the process
-		 * of getting flushed to disk, we don't want to reclaim it.
-		 */
-		if (!xfs_dqflock_nowait(dqp))
-			goto dqunlock;
+	ASSERT(dqp->q_hash);
+	ASSERT(!list_empty(&dqp->q_mplist));
 
-		/*
-		 * We have the flush lock so we know that this is not in the
-		 * process of being flushed. So, if this is dirty, flush it
-		 * DELWRI so that we don't get a freelist infested with
-		 * dirty dquots.
-		 */
-		if (XFS_DQ_IS_DIRTY(dqp)) {
-			int	error;
+	/*
+	 * Try to grab the flush lock. If this dquot is in the process of
+	 * getting flushed to disk, we don't want to reclaim it.
+	 */
+	if (!xfs_dqflock_nowait(dqp))
+		goto out_busy;
 
-			trace_xfs_dqreclaim_dirty(dqp);
+	/*
+	 * We have the flush lock so we know that this is not in the
+	 * process of being flushed. So, if this is dirty, flush it
+	 * DELWRI so that we don't get a freelist infested with
+	 * dirty dquots.
+	 */
+	if (XFS_DQ_IS_DIRTY(dqp)) {
+		trace_xfs_dqreclaim_dirty(dqp);
 
-			/*
-			 * We flush it delayed write, so don't bother
-			 * releasing the freelist lock.
-			 */
-			error = xfs_qm_dqflush(dqp, SYNC_TRYLOCK);
-			if (error) {
-				xfs_warn(mp, "%s: dquot %p flush failed",
-					__func__, dqp);
-			}
-			goto dqunlock;
+		/*
+		 * We flush it delayed write, so don't bother releasing the
+		 * freelist lock.
+		 */
+		error = xfs_qm_dqflush(dqp, 0);
+		if (error) {
+			xfs_warn(mp, "%s: dquot %p flush failed",
+				 __func__, dqp);
 		}
-		xfs_dqfunlock(dqp);
 
 		/*
-		 * Prevent lookup now that we are going to reclaim the dquot.
-		 * Once XFS_DQ_FREEING is set lookup won't touch the dquot,
-		 * thus we can drop the lock now.
+		 * Give the dquot another try on the freelist, as the
+		 * flushing will take some time.
 		 */
-		dqp->dq_flags |= XFS_DQ_FREEING;
-		xfs_dqunlock(dqp);
-
-		mutex_lock(&dqp->q_hash->qh_lock);
-		list_del_init(&dqp->q_hashlist);
-		dqp->q_hash->qh_version++;
-		mutex_unlock(&dqp->q_hash->qh_lock);
-
-		mutex_lock(&mp->m_quotainfo->qi_dqlist_lock);
-		list_del_init(&dqp->q_mplist);
-		mp->m_quotainfo->qi_dquots--;
-		mp->m_quotainfo->qi_dqreclaims++;
-		mutex_unlock(&mp->m_quotainfo->qi_dqlist_lock);
+		goto out_busy;
+	}
+	xfs_dqfunlock(dqp);
 
-		ASSERT(dqp->q_nrefs == 0);
-		list_del_init(&dqp->q_freelist);
-		xfs_Gqm->qm_dqfrlist_cnt--;
+	/*
+	 * Prevent lookups now that we are past the point of no return.
+	 */
+	dqp->dq_flags |= XFS_DQ_FREEING;
+	xfs_dqunlock(dqp);
 
-		mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
-		return dqp;
-dqunlock:
-		xfs_dqunlock(dqp);
-		if (restarts >= XFS_QM_RECLAIM_MAX_RESTARTS)
-			break;
-		goto restart;
-	}
+	ASSERT(dqp->q_nrefs == 0);
+	list_move_tail(&dqp->q_freelist, dispose_list);
+	xfs_Gqm->qm_dqfrlist_cnt--;
 
-	mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
-	return NULL;
-}
+	trace_xfs_dqreclaim_done(dqp);
+	XQM_STATS_INC(xqmstats.xs_qm_dqreclaims);
+	return;
 
-/*
- * Traverse the freelist of dquots and attempt to reclaim a maximum of
- * 'howmany' dquots. This operation races with dqlookup(), and attempts to
- * favor the lookup function ...
- */
-STATIC int
-xfs_qm_shake_freelist(
-	int	howmany)
-{
-	int		nreclaimed = 0;
-	xfs_dquot_t	*dqp;
+out_busy:
+	xfs_dqunlock(dqp);
 
-	if (howmany <= 0)
-		return 0;
+	/*
+	 * Move the dquot to the tail of the list so that we don't spin on it.
+	 */
+	list_move_tail(&dqp->q_freelist, &xfs_Gqm->qm_dqfrlist);
 
-	while (nreclaimed < howmany) {
-		dqp = xfs_qm_dqreclaim_one();
-		if (!dqp)
-			return nreclaimed;
-		xfs_qm_dqdestroy(dqp);
-		nreclaimed++;
-	}
-	return nreclaimed;
+	trace_xfs_dqreclaim_busy(dqp);
+	XQM_STATS_INC(xqmstats.xs_qm_dqreclaim_misses);
 }
 
-/*
- * The kmem_shake interface is invoked when memory is running low.
- */
-/* ARGSUSED */
 STATIC int
 xfs_qm_shake(
-	struct shrinker	*shrink,
-	struct shrink_control *sc)
+	struct shrinker		*shrink,
+	struct shrink_control	*sc)
 {
-	int	ndqused, nfree, n;
-	gfp_t gfp_mask = sc->gfp_mask;
-
-	if (!kmem_shake_allow(gfp_mask))
-		return 0;
-	if (!xfs_Gqm)
-		return 0;
-
-	nfree = xfs_Gqm->qm_dqfrlist_cnt; /* free dquots */
-	/* incore dquots in all f/s's */
-	ndqused = atomic_read(&xfs_Gqm->qm_totaldquots) - nfree;
-
-	ASSERT(ndqused >= 0);
+	int			nr_to_scan = sc->nr_to_scan;
+	LIST_HEAD		(dispose_list);
+	struct xfs_dquot	*dqp;
 
-	if (nfree <= ndqused && nfree < ndquot)
+	if ((sc->gfp_mask & (__GFP_FS|__GFP_WAIT)) != (__GFP_FS|__GFP_WAIT))
 		return 0;
+	if (!nr_to_scan)
+		goto out;
 
-	ndqused *= xfs_Gqm->qm_dqfree_ratio;	/* target # of free dquots */
-	n = nfree - ndqused - ndquot;		/* # over target */
-
-	return xfs_qm_shake_freelist(MAX(nfree, n));
-}
-
-
-/*------------------------------------------------------------------*/
-
-/*
- * Return a new incore dquot. Depending on the number of
- * dquots in the system, we either allocate a new one on the kernel heap,
- * or reclaim a free one.
- * Return value is B_TRUE if we allocated a new dquot, B_FALSE if we managed
- * to reclaim an existing one from the freelist.
- */
-boolean_t
-xfs_qm_dqalloc_incore(
-	xfs_dquot_t **O_dqpp)
-{
-	xfs_dquot_t	*dqp;
-
-	/*
-	 * Check against high water mark to see if we want to pop
-	 * a nincompoop dquot off the freelist.
-	 */
-	if (atomic_read(&xfs_Gqm->qm_totaldquots) >= ndquot) {
-		/*
-		 * Try to recycle a dquot from the freelist.
-		 */
-		if ((dqp = xfs_qm_dqreclaim_one())) {
-			XQM_STATS_INC(xqmstats.xs_qm_dqreclaims);
-			/*
-			 * Just zero the core here. The rest will get
-			 * reinitialized by caller. XXX we shouldn't even
-			 * do this zero ...
-			 */
-			memset(&dqp->q_core, 0, sizeof(dqp->q_core));
-			*O_dqpp = dqp;
-			return B_FALSE;
-		}
-		XQM_STATS_INC(xqmstats.xs_qm_dqreclaim_misses);
+	mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
+	while (!list_empty(&xfs_Gqm->qm_dqfrlist)) {
+		if (nr_to_scan-- <= 0)
+			break;
+		dqp = list_first_entry(&xfs_Gqm->qm_dqfrlist, struct xfs_dquot,
+				       q_freelist);
+		xfs_qm_dqreclaim_one(dqp, &dispose_list);
 	}
+	mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
 
-	/*
-	 * Allocate a brand new dquot on the kernel heap and return it
-	 * to the caller to initialize.
-	 */
-	ASSERT(xfs_Gqm->qm_dqzone != NULL);
-	*O_dqpp = kmem_zone_zalloc(xfs_Gqm->qm_dqzone, KM_SLEEP);
-	atomic_inc(&xfs_Gqm->qm_totaldquots);
-
-	return B_TRUE;
+	while (!list_empty(&dispose_list)) {
+		dqp = list_first_entry(&dispose_list, struct xfs_dquot,
+				       q_freelist);
+		list_del_init(&dqp->q_freelist);
+		xfs_qm_dqfree_one(dqp);
+	}
+out:
+	return (xfs_Gqm->qm_dqfrlist_cnt / 100) * sysctl_vfs_cache_pressure;
 }
 
-
 /*
  * Start a transaction and write the incore superblock changes to
  * disk. flags parameter indicates which fields have changed.