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SubjectRe: [patch] slab: revert "slab: fix alien cache handling"
On Mon, Aug 13, 2007 at 01:58:48PM -0700, Christoph Lameter wrote:
> On Mon, 13 Aug 2007, Siddha, Suresh B wrote:
>
> > Can we revert git commit 3cdc0ed0cea50ea08dd146c1bbc82b1bcc2e1b80 ?
>
> Only if you find another way to fix the bug that is addressed there.

Does the appended version fix both the issues? Name alien in cache_free_alien
is confusing, as the function does two things. free through alien caches
or direct remote free..

thanks,
suresh
---

Skip calling cache_free_alien() when the platform is not numa capable.
This will avoid cache misses that happen while accessing slabp (which
is per page memory reference) to get nodeid. Instead use a global
variable to skip the call, which is mostly likely to be present in the
cache.

This gives a 0.8% performance boost with the database oltp workload
on a quad-core SMP platform and by any means the number is not small :)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---

diff --git a/mm/slab.c b/mm/slab.c
index a684778..6f6abef 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -883,6 +883,7 @@ static void __slab_error(const char *function, struct kmem_cache *cachep,
*/

static int use_alien_caches __read_mostly = 1;
+static int numa_platform __read_mostly = 1;
static int __init noaliencache_setup(char *s)
{
use_alien_caches = 0;
@@ -1399,8 +1400,10 @@ void __init kmem_cache_init(void)
int order;
int node;

- if (num_possible_nodes() == 1)
+ if (num_possible_nodes() == 1) {
use_alien_caches = 0;
+ numa_platform = 0;
+ }

for (i = 0; i < NUM_INIT_LISTS; i++) {
kmem_list3_init(&initkmem_list3[i]);
@@ -3558,7 +3561,14 @@ static inline void __cache_free(struct kmem_cache *cachep, void *objp)
check_irq_off();
objp = cache_free_debugcheck(cachep, objp, __builtin_return_address(0));

- if (cache_free_alien(cachep, objp))
+ /*
+ * Skip calling cache_free_alien() when the platform is not numa.
+ * This will avoid cache misses that happen while accessing slabp (which
+ * is per page memory reference) to get nodeid. Instead use a global
+ * variable to skip the call, which is mostly likely to be present in
+ * the cache.
+ */
+ if (numa_platform && cache_free_alien(cachep, objp))
return;

if (likely(ac->avail < ac->limit)) {
-
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