xfs: serialise inode reclaim within an AG
Memory reclaim via shrinkers has a terrible habit of having N+M concurrent shrinker executions (N = num CPUs, M = num kswapds) all trying to shrink the same cache. When the cache they are all working on is protected by a single spinlock, massive contention an slowdowns occur. Wrap the per-ag inode caches with a reclaim mutex to serialise reclaim access to the AG. This will block concurrent reclaim in each AG but still allow reclaim to scan multiple AGs concurrently. Allow shrinkers to move on to the next AG if it can't get the lock, and if we can't get any AG, then start blocking on locks. To prevent reclaimers from continually scanning the same inodes in each AG, add a cursor that tracks where the last reclaim got up to and start from that point on the next reclaim. This should avoid only ever scanning a small number of inodes at the satart of each AG and not making progress. If we have a non-shrinker based reclaim pass, ignore the cursor and reset it to zero once we are done. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Alex Elder <aelder@sgi.com>
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@ -837,8 +837,12 @@ xfs_reclaim_inodes_ag(
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int error = 0;
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int last_error = 0;
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xfs_agnumber_t ag;
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int trylock = flags & SYNC_TRYLOCK;
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int skipped;
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restart:
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ag = 0;
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skipped = 0;
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while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
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unsigned long first_index = 0;
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int done = 0;
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@ -846,6 +850,15 @@ xfs_reclaim_inodes_ag(
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ag = pag->pag_agno + 1;
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if (trylock) {
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if (!mutex_trylock(&pag->pag_ici_reclaim_lock)) {
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skipped++;
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continue;
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}
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first_index = pag->pag_ici_reclaim_cursor;
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} else
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mutex_lock(&pag->pag_ici_reclaim_lock);
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do {
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struct xfs_inode *batch[XFS_LOOKUP_BATCH];
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int i;
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@ -898,8 +911,25 @@ xfs_reclaim_inodes_ag(
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} while (nr_found && !done && *nr_to_scan > 0);
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if (trylock && !done)
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pag->pag_ici_reclaim_cursor = first_index;
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else
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pag->pag_ici_reclaim_cursor = 0;
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mutex_unlock(&pag->pag_ici_reclaim_lock);
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xfs_perag_put(pag);
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}
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/*
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* if we skipped any AG, and we still have scan count remaining, do
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* another pass this time using blocking reclaim semantics (i.e
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* waiting on the reclaim locks and ignoring the reclaim cursors). This
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* ensure that when we get more reclaimers than AGs we block rather
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* than spin trying to execute reclaim.
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*/
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if (trylock && skipped && *nr_to_scan > 0) {
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trylock = 0;
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goto restart;
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}
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return XFS_ERROR(last_error);
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}
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@ -230,6 +230,8 @@ typedef struct xfs_perag {
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rwlock_t pag_ici_lock; /* incore inode lock */
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struct radix_tree_root pag_ici_root; /* incore inode cache root */
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int pag_ici_reclaimable; /* reclaimable inodes */
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struct mutex pag_ici_reclaim_lock; /* serialisation point */
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unsigned long pag_ici_reclaim_cursor; /* reclaim restart point */
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/* for rcu-safe freeing */
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struct rcu_head rcu_head;
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@ -477,6 +477,7 @@ xfs_initialize_perag(
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pag->pag_agno = index;
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pag->pag_mount = mp;
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rwlock_init(&pag->pag_ici_lock);
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mutex_init(&pag->pag_ici_reclaim_lock);
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INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
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if (radix_tree_preload(GFP_NOFS))
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