Re: [PATCH] Locking optimization for cache_reap
From: Andrew Morton <hidden>
Date: 2004-07-27 01:04:37
Also in:
lkml
Dimitri Sivanich [off-list ref] wrote:
Here is another cache_reap optimization that reduces latency when applied after the 'Move cache_reap out of timer context' patch I submitted on 7/14 (for inclusion in -mm next week). This applies to 2.6.8-rc2 + the above mentioned patch.
How does it "reduce latency"? It looks like a reasonable cleanup, but afaict it will result in the per-cache spinlock actually being held for longer periods, thus increasing latencies???
quoted hunk ↗ jump to hunk
Index: linux/mm/slab.c ===================================================================--- linux.orig/mm/slab.c +++ linux/mm/slab.c@@ -2619,27 +2619,6 @@ static void enable_cpucache (kmem_cache_ cachep->name, -err); } -static void drain_array(kmem_cache_t *cachep, struct array_cache *ac) -{ - int tofree; - - check_irq_off(); - if (ac->touched) { - ac->touched = 0; - } else if (ac->avail) { - tofree = (ac->limit+4)/5; - if (tofree > ac->avail) { - tofree = (ac->avail+1)/2; - } - spin_lock(&cachep->spinlock); - free_block(cachep, ac_entry(ac), tofree); - spin_unlock(&cachep->spinlock); - ac->avail -= tofree; - memmove(&ac_entry(ac)[0], &ac_entry(ac)[tofree], - sizeof(void*)*ac->avail); - } -} - static void drain_array_locked(kmem_cache_t *cachep, struct array_cache *ac, int force) {@@ -2697,16 +2676,14 @@ static void cache_reap (void *unused) goto next; check_irq_on(); - local_irq_disable(); - drain_array(searchp, ac_data(searchp)); - if(time_after(searchp->lists.next_reap, jiffies)) - goto next_irqon; + spin_lock_irq(&searchp->spinlock); + + drain_array_locked(searchp, ac_data(searchp), 0); - spin_lock(&searchp->spinlock); - if(time_after(searchp->lists.next_reap, jiffies)) { + if(time_after(searchp->lists.next_reap, jiffies)) goto next_unlock; - } + searchp->lists.next_reap = jiffies + REAPTIMEOUT_LIST3; if (searchp->lists.shared)@@ -2739,9 +2716,7 @@ static void cache_reap (void *unused) spin_lock_irq(&searchp->spinlock); } while(--tofree > 0); next_unlock: - spin_unlock(&searchp->spinlock); -next_irqon: - local_irq_enable(); + spin_unlock_irq(&searchp->spinlock); next: ; }
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