From 5b9f3b7664b59375481148c078bd29d5c9e07de2 Mon Sep 17 00:00:00 2001 From: Alexander Motin Date: Thu, 8 Aug 2024 18:26:35 -0400 Subject: [PATCH] Soften pruning threshold on not evictable metadata Previous code pruned 10% of dnodes once 3/4 of metadata appeared unevictable. On workloads with many millions of dnodes and little other metadata it creates significant load spikes for many seconds straight. This change instead gradually increases pruning as unevictable metadata grow above the 3/4, which may allow it to stabilize at some level. Reviewed-by: Brian Behlendorf Signed-off-by: Alexander Motin Sponsored by: iXsystems, Inc. Closes #16401 --- module/zfs/arc.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 9bb7eeef32..78c2cf8ec5 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -4235,6 +4235,18 @@ arc_evict_adj(uint64_t frac, uint64_t total, uint64_t up, uint64_t down, return (frac + up - down); } +/* + * Calculate (x * multiplier / divisor) without unnecesary overflows. + */ +static uint64_t +arc_mf(uint64_t x, uint64_t multiplier, uint64_t divisor) +{ + uint64_t q = (x / divisor); + uint64_t r = (x % divisor); + + return ((q * multiplier) + ((r * multiplier) / divisor)); +} + /* * Evict buffers from the cache, such that arcstat_size is capped by arc_c. */ @@ -4287,17 +4299,20 @@ arc_evict(void) */ int64_t prune = 0; int64_t dn = wmsum_value(&arc_sums.arcstat_dnode_size); + int64_t nem = zfs_refcount_count(&arc_mru->arcs_size[ARC_BUFC_METADATA]) + + zfs_refcount_count(&arc_mfu->arcs_size[ARC_BUFC_METADATA]) + - zfs_refcount_count(&arc_mru->arcs_esize[ARC_BUFC_METADATA]) + - zfs_refcount_count(&arc_mfu->arcs_esize[ARC_BUFC_METADATA]); w = wt * (int64_t)(arc_meta >> 16) >> 16; - if (zfs_refcount_count(&arc_mru->arcs_size[ARC_BUFC_METADATA]) + - zfs_refcount_count(&arc_mfu->arcs_size[ARC_BUFC_METADATA]) - - zfs_refcount_count(&arc_mru->arcs_esize[ARC_BUFC_METADATA]) - - zfs_refcount_count(&arc_mfu->arcs_esize[ARC_BUFC_METADATA]) > - w * 3 / 4) { + if (nem > w * 3 / 4) { prune = dn / sizeof (dnode_t) * zfs_arc_dnode_reduce_percent / 100; - } else if (dn > arc_dnode_limit) { - prune = (dn - arc_dnode_limit) / sizeof (dnode_t) * - zfs_arc_dnode_reduce_percent / 100; + if (nem < w && w > 4) + prune = arc_mf(prune, nem - w * 3 / 4, w / 4); + } + if (dn > arc_dnode_limit) { + prune = MAX(prune, (dn - arc_dnode_limit) / sizeof (dnode_t) * + zfs_arc_dnode_reduce_percent / 100); } if (prune > 0) arc_prune_async(prune);