diff options
| author | Hao Li <hao.li@linux.dev> | 2026-05-29 11:50:52 +0800 |
|---|---|---|
| committer | Vlastimil Babka (SUSE) <vbabka@kernel.org> | 2026-05-29 09:58:35 +0200 |
| commit | 2221dcc5a24f5d4472a099f67fc9c2aeb2556493 (patch) | |
| tree | 68cfd32d4432ee8d42515d7cfe62357f7e6535cc /mm | |
| parent | 6c63102006001c8578cf61dc07bc025f7e909be7 (diff) | |
| download | linux-next-history-2221dcc5a24f5d4472a099f67fc9c2aeb2556493.tar.gz | |
mm/slub: detach and reattach partial slabs in batch
get_partial_node_bulk() moves each selected slab from the node's
partial list to the local pc->slabs list using a remove_partial() and
list_add() pair. In practice, the loop often detaches several adjacent
slabs. Doing this individually repeatedly manipulates list pointers
while holding n->list_lock, which causes unnecessary churn.
To demonstrate this, the counts below show how often single vs. multiple
consecutive slabs are retrieved during a will-it-scale mmap stress test:
consecutive_slabs_count frequency
= 1 277345324
= 2 335238023
= 3 175717884
>= 4 88862337
The data confirms that retrieving multiple contiguous slabs is highly
frequent.
To optimize this, track contiguous runs of matching slabs and move each
run in a single operation using list_bulk_move_tail(). This reduces list
pointer churn inside the lock critical section.
Apply the same optimization to __refill_objects_node() when reattaching
leftover partial slabs back to the node's partial list.
The will-it-scale mmap benchmark shows a 2% ~ 5% performance improvement
after applying this patch.
Signed-off-by: Hao Li <hao.li@linux.dev>
Link: https://patch.msgid.link/20260529035120.81304-3-hao.li@linux.dev
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/slub.c | 28 |
1 files changed, 20 insertions, 8 deletions
diff --git a/mm/slub.c b/mm/slub.c index f9a4da5363564..492128ae3af95 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3751,6 +3751,7 @@ static bool get_partial_node_bulk(struct kmem_cache *s, bool allow_spin) { struct slab *slab, *slab2; + struct slab *first = NULL, *last = NULL; unsigned int total_free = 0; unsigned long flags; @@ -3769,8 +3770,15 @@ static bool get_partial_node_bulk(struct kmem_cache *s, struct freelist_counters flc; unsigned int slab_free; - if (!pfmemalloc_match(slab, pc->flags)) + if (!pfmemalloc_match(slab, pc->flags)) { + if (first) { + list_bulk_move_tail(&pc->slabs, + &first->slab_list, + &last->slab_list); + first = NULL; + } continue; + } /* * determine the number of free objects in the slab racily @@ -3787,15 +3795,20 @@ static bool get_partial_node_bulk(struct kmem_cache *s, && total_free + slab_free > pc->max_objects) break; - remove_partial(n, slab); - - list_add(&slab->slab_list, &pc->slabs); + if (!first) + first = slab; + last = slab; + clear_node_partial_state(n, slab); total_free += slab_free; if (total_free >= pc->max_objects) break; } + if (first) + list_bulk_move_tail(&pc->slabs, &first->slab_list, + &last->slab_list); + spin_unlock_irqrestore(&n->list_lock, flags); return total_free > 0; } @@ -7205,11 +7218,10 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi if (!list_empty(&pc.slabs)) { spin_lock_irqsave(&n->list_lock, flags); - list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) { + list_for_each_entry(slab, &pc.slabs, slab_list) + set_node_partial_state(n, slab); - list_del(&slab->slab_list); - add_partial(n, slab, ADD_TO_TAIL); - } + list_splice_tail(&pc.slabs, &n->partial); spin_unlock_irqrestore(&n->list_lock, flags); } |