This implements SLUB specific kmem_cache_free_bulk(). SLUB allocator
now both have bulk alloc and free implemented.
Choose to reenable local IRQs while calling slowpath __slab_free().
In worst case, where all objects hit slowpath call, the performance
should still be faster than fallback function __kmem_cache_free_bulk(),
because local_irq_{disable+enable} is very fast (7-cycles), while the
fallback invokes this_cpu_cmpxchg() which is slightly slower
(9-cycles). Nitpicking, this should be faster for N>=4, due to the
entry cost of local_irq_{disable+enable}.
Do notice that the save+restore variant is very expensive, this is key
to why this optimization works.
CPU: i7-4790K CPU @ 4.00GHz
* local_irq_{disable,enable}: 7 cycles(tsc) - 1.821 ns
* local_irq_{save,restore} : 37 cycles(tsc) - 9.443 ns
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
V2:
- Add BUG_ON(!object)
- No support for kmem_cache_debug()
Measurements on CPU CPU i7-4790K @ 4.00GHz
Baseline normal fastpath (alloc+free cost): 43 cycles(tsc) 10.834 ns
Bulk- fallback - this-patch
1 - 58 cycles(tsc) 14.542 ns - 43 cycles(tsc) 10.811 ns improved 25.9%
2 - 50 cycles(tsc) 12.659 ns - 27 cycles(tsc) 6.867 ns improved 46.0%
3 - 48 cycles(tsc) 12.168 ns - 21 cycles(tsc) 5.496 ns improved 56.2%
4 - 47 cycles(tsc) 11.987 ns - 24 cycles(tsc) 6.038 ns improved 48.9%
8 - 46 cycles(tsc) 11.518 ns - 17 cycles(tsc) 4.280 ns improved 63.0%
16 - 45 cycles(tsc) 11.366 ns - 17 cycles(tsc) 4.483 ns improved 62.2%
30 - 45 cycles(tsc) 11.433 ns - 18 cycles(tsc) 4.531 ns improved 60.0%
32 - 75 cycles(tsc) 18.983 ns - 58 cycles(tsc) 14.586 ns improved 22.7%
34 - 71 cycles(tsc) 17.940 ns - 53 cycles(tsc) 13.391 ns improved 25.4%
48 - 80 cycles(tsc) 20.077 ns - 65 cycles(tsc) 16.268 ns improved 18.8%
64 - 71 cycles(tsc) 17.799 ns - 53 cycles(tsc) 13.440 ns improved 25.4%
128 - 91 cycles(tsc) 22.980 ns - 79 cycles(tsc) 19.899 ns improved 13.2%
158 - 100 cycles(tsc) 25.241 ns - 90 cycles(tsc) 22.732 ns improved 10.0%
250 - 102 cycles(tsc) 25.583 ns - 95 cycles(tsc) 23.916 ns improved 6.9%
mm/slub.c | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c
index 02c33bacd3a6..6ac5921b3389 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2753,7 +2753,39 @@ EXPORT_SYMBOL(kmem_cache_free);
/* Note that interrupts must be enabled when calling this function. */
void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
{
- __kmem_cache_free_bulk(s, size, p);
+ struct kmem_cache_cpu *c;
+ struct page *page;
+ int i;
+
+ /* Debugging fallback to generic bulk */
+ if (kmem_cache_debug(s))
+ return __kmem_cache_free_bulk(s, size, p);
+
+ local_irq_disable();
+ c = this_cpu_ptr(s->cpu_slab);
+
+ for (i = 0; i < size; i++) {
+ void *object = p[i];
+
+ BUG_ON(!object);
+ page = virt_to_head_page(object);
+ BUG_ON(s != page->slab_cache); /* Check if valid slab page */
+
+ if (c->page == page) {
+ /* Fastpath: local CPU free */
+ set_freepointer(s, object, c->freelist);
+ c->freelist = object;
+ } else {
+ c->tid = next_tid(c->tid);
+ local_irq_enable();
+ /* Slowpath: overhead locked cmpxchg_double_slab */
+ __slab_free(s, page, object, _RET_IP_);
+ local_irq_disable();
+ c = this_cpu_ptr(s->cpu_slab);
+ }
+ }
+ c->tid = next_tid(c->tid);
+ local_irq_enable();
}
EXPORT_SYMBOL(kmem_cache_free_bulk);
--
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