The node list_lock in count_partial() spend long time iterating in case of large amount of partial page lists, which can cause thunder herd effect to the list_lock contention, e.g. it cause business response-time jitters when accessing "/proc/slabinfo" in our production environments.
This patch introduces two counters to maintain the actual number of partial objects dynamically instead of iterating the partial page lists with list_lock held. New counters of kmem_cache_node are: pfree_objects, ptotal_objects. The main operations are under list_lock in slow path, its performance impact is minimal. Co-developed-by: Wen Yang <[email protected]> Signed-off-by: Xunlei Pang <[email protected]> --- mm/slab.h | 2 ++ mm/slub.c | 38 +++++++++++++++++++++++++++++++++++++- 2 files changed, 39 insertions(+), 1 deletion(-) diff --git a/mm/slab.h b/mm/slab.h index 7e94700..5935749 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -616,6 +616,8 @@ struct kmem_cache_node { #ifdef CONFIG_SLUB unsigned long nr_partial; struct list_head partial; + atomic_long_t pfree_objects; /* partial free objects */ + atomic_long_t ptotal_objects; /* partial total objects */ #ifdef CONFIG_SLUB_DEBUG atomic_long_t nr_slabs; atomic_long_t total_objects; diff --git a/mm/slub.c b/mm/slub.c index 6589b41..53890f3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1775,10 +1775,24 @@ static void discard_slab(struct kmem_cache *s, struct page *page) /* * Management of partially allocated slabs. */ + +static inline void +__update_partial_free(struct kmem_cache_node *n, long delta) +{ + atomic_long_add(delta, &n->pfree_objects); +} + +static inline void +__update_partial_total(struct kmem_cache_node *n, long delta) +{ + atomic_long_add(delta, &n->ptotal_objects); +} + static inline void __add_partial(struct kmem_cache_node *n, struct page *page, int tail) { n->nr_partial++; + __update_partial_total(n, page->objects); if (tail == DEACTIVATE_TO_TAIL) list_add_tail(&page->slab_list, &n->partial); else @@ -1798,6 +1812,7 @@ static inline void remove_partial(struct kmem_cache_node *n, lockdep_assert_held(&n->list_lock); list_del(&page->slab_list); n->nr_partial--; + __update_partial_total(n, -page->objects); } /* @@ -1842,6 +1857,7 @@ static inline void *acquire_slab(struct kmem_cache *s, return NULL; remove_partial(n, page); + __update_partial_free(n, -*objects); WARN_ON(!freelist); return freelist; } @@ -2174,8 +2190,11 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page, "unfreezing slab")) goto redo; - if (lock) + if (lock) { + if (m == M_PARTIAL) + __update_partial_free(n, page->objects - page->inuse); spin_unlock(&n->list_lock); + } if (m == M_PARTIAL) stat(s, tail); @@ -2241,6 +2260,7 @@ static void unfreeze_partials(struct kmem_cache *s, discard_page = page; } else { add_partial(n, page, DEACTIVATE_TO_TAIL); + __update_partial_free(n, page->objects - page->inuse); stat(s, FREE_ADD_PARTIAL); } } @@ -2915,6 +2935,14 @@ static void __slab_free(struct kmem_cache *s, struct page *page, head, new.counters, "__slab_free")); + if (!was_frozen && prior) { + if (n) + __update_partial_free(n, cnt); + else + __update_partial_free(get_node(s, page_to_nid(page)), + cnt); + } + if (likely(!n)) { /* @@ -2944,6 +2972,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page, if (!kmem_cache_has_cpu_partial(s) && unlikely(!prior)) { remove_full(s, n, page); add_partial(n, page, DEACTIVATE_TO_TAIL); + __update_partial_free(n, page->objects - page->inuse); stat(s, FREE_ADD_PARTIAL); } spin_unlock_irqrestore(&n->list_lock, flags); @@ -2955,6 +2984,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page, * Slab on the partial list. */ remove_partial(n, page); + __update_partial_free(n, page->inuse - page->objects); stat(s, FREE_REMOVE_PARTIAL); } else { /* Slab must be on the full list */ @@ -3364,6 +3394,8 @@ static inline int calculate_order(unsigned int size) n->nr_partial = 0; spin_lock_init(&n->list_lock); INIT_LIST_HEAD(&n->partial); + atomic_long_set(&n->pfree_objects, 0); + atomic_long_set(&n->ptotal_objects, 0); #ifdef CONFIG_SLUB_DEBUG atomic_long_set(&n->nr_slabs, 0); atomic_long_set(&n->total_objects, 0); @@ -3437,6 +3469,7 @@ static void early_kmem_cache_node_alloc(int node) * initialized and there is no concurrent access. */ __add_partial(n, page, DEACTIVATE_TO_HEAD); + __update_partial_free(n, page->objects - page->inuse); } static void free_kmem_cache_nodes(struct kmem_cache *s) @@ -3747,6 +3780,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n) list_for_each_entry_safe(page, h, &n->partial, slab_list) { if (!page->inuse) { remove_partial(n, page); + __update_partial_free(n, page->objects - page->inuse); list_add(&page->slab_list, &discard); } else { list_slab_objects(s, page, @@ -4045,6 +4079,8 @@ int __kmem_cache_shrink(struct kmem_cache *s) if (free == page->objects) { list_move(&page->slab_list, &discard); n->nr_partial--; + __update_partial_free(n, -free); + __update_partial_total(n, -free); } else if (free <= SHRINK_PROMOTE_MAX) list_move(&page->slab_list, promote + free - 1); } -- 1.8.3.1
