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enforce arc_dnode_limit

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Linux kernel shrinker in the context of null/root memcg does not scan
dentry and inode caches added by a task running in non-root memcg. For
ZFS this means that dnode cache routinely overflows, evicting valuable
meta/data and putting additional memory pressure on the system.

This patch restores zfs_prune_aliases as fallback when the kernel
shrinker does nothing, enabling zfs to actually free dnodes. Moreover,
it (indirectly) calls arc_evict when dnode_size > dnode_limit.

Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Gionatan Danti <g.danti@assyoma.it>
Closes #17487
Closes #17542
This commit is contained in:
shodanshok
2025-07-21 19:32:01 +02:00
committed by GitHub
parent be1e991a1a
commit a7a144e655
3 changed files with 78 additions and 11 deletions
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module/zfs/arc.c
+12 -10
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@@ -2631,7 +2631,7 @@ arc_space_consume(uint64_t space, arc_space_type_t type)
ARCSTAT_INCR(arcstat_bonus_size, space);
break;
case ARC_SPACE_DNODE:
ARCSTAT_INCR(arcstat_dnode_size, space);
aggsum_add(&arc_sums.arcstat_dnode_size, space);
break;
case ARC_SPACE_DBUF:
ARCSTAT_INCR(arcstat_dbuf_size, space);
@@ -2677,7 +2677,7 @@ arc_space_return(uint64_t space, arc_space_type_t type)
ARCSTAT_INCR(arcstat_bonus_size, -space);
break;
case ARC_SPACE_DNODE:
ARCSTAT_INCR(arcstat_dnode_size, -space);
aggsum_add(&arc_sums.arcstat_dnode_size, -space);
break;
case ARC_SPACE_DBUF:
ARCSTAT_INCR(arcstat_dbuf_size, -space);
@@ -4490,7 +4490,7 @@ arc_evict(void)
* target is not evictable or if they go over arc_dnode_limit.
*/
int64_t prune = 0;
int64_t dn = wmsum_value(&arc_sums.arcstat_dnode_size);
int64_t dn = aggsum_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])
@@ -5082,11 +5082,13 @@ arc_is_overflowing(boolean_t lax, boolean_t use_reserve)
* in the ARC. In practice, that's in the tens of MB, which is low
* enough to be safe.
*/
int64_t over = aggsum_lower_bound(&arc_sums.arcstat_size) - arc_c -
int64_t arc_over = aggsum_lower_bound(&arc_sums.arcstat_size) - arc_c -
zfs_max_recordsize;
int64_t dn_over = aggsum_lower_bound(&arc_sums.arcstat_dnode_size) -
arc_dnode_limit;
/* Always allow at least one block of overflow. */
if (over < 0)
if (arc_over < 0 && dn_over <= 0)
return (ARC_OVF_NONE);
/* If we are under memory pressure, report severe overflow. */
@@ -5097,7 +5099,7 @@ arc_is_overflowing(boolean_t lax, boolean_t use_reserve)
int64_t overflow = (arc_c >> zfs_arc_overflow_shift) / 2;
if (use_reserve)
overflow *= 3;
return (over < overflow ? ARC_OVF_SOME : ARC_OVF_SEVERE);
return (arc_over < overflow ? ARC_OVF_SOME : ARC_OVF_SEVERE);
}
static abd_t *
@@ -7326,7 +7328,7 @@ arc_kstat_update(kstat_t *ksp, int rw)
#if defined(COMPAT_FREEBSD11)
as->arcstat_other_size.value.ui64 =
wmsum_value(&arc_sums.arcstat_bonus_size) +
wmsum_value(&arc_sums.arcstat_dnode_size) +
aggsum_value(&arc_sums.arcstat_dnode_size) +
wmsum_value(&arc_sums.arcstat_dbuf_size);
#endif
@@ -7368,7 +7370,7 @@ arc_kstat_update(kstat_t *ksp, int rw)
&as->arcstat_uncached_evictable_metadata);
as->arcstat_dnode_size.value.ui64 =
wmsum_value(&arc_sums.arcstat_dnode_size);
aggsum_value(&arc_sums.arcstat_dnode_size);
as->arcstat_bonus_size.value.ui64 =
wmsum_value(&arc_sums.arcstat_bonus_size);
as->arcstat_l2_hits.value.ui64 =
@@ -7738,7 +7740,7 @@ arc_state_init(void)
wmsum_init(&arc_sums.arcstat_data_size, 0);
wmsum_init(&arc_sums.arcstat_metadata_size, 0);
wmsum_init(&arc_sums.arcstat_dbuf_size, 0);
wmsum_init(&arc_sums.arcstat_dnode_size, 0);
aggsum_init(&arc_sums.arcstat_dnode_size, 0);
wmsum_init(&arc_sums.arcstat_bonus_size, 0);
wmsum_init(&arc_sums.arcstat_l2_hits, 0);
wmsum_init(&arc_sums.arcstat_l2_misses, 0);
@@ -7897,7 +7899,7 @@ arc_state_fini(void)
wmsum_fini(&arc_sums.arcstat_data_size);
wmsum_fini(&arc_sums.arcstat_metadata_size);
wmsum_fini(&arc_sums.arcstat_dbuf_size);
wmsum_fini(&arc_sums.arcstat_dnode_size);
aggsum_fini(&arc_sums.arcstat_dnode_size);
wmsum_fini(&arc_sums.arcstat_bonus_size);
wmsum_fini(&arc_sums.arcstat_l2_hits);
wmsum_fini(&arc_sums.arcstat_l2_misses);