[patch 04/10] SLUB: Avoid checking for a valid object before zeroing on the fast path

Christoph Lameter
2007-10-28T03:34:43Z

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The fast path always results in a valid object. Move the check
for the NULL pointer to the slow branch that calls
__slab_alloc. Only __slab_alloc can return NULL if there is no
memory available anymore and that case is exceedingly rare.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
mm/slub.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2007-10-25 19:37:38.000000000 -0700
+++ linux-2.6/mm/slub.c 2007-10-25 19:38:14.000000000 -0700
@@ -1573,19 +1573,22 @@ static void __always_inline *slab_alloc(

local_irq_save(flags);
c = get_cpu_slab(s, smp_processor_id());
- if (unlikely(!c->freelist || !node_match(c, node)))
+ if (unlikely(!c->freelist || !node_match(c, node))) {

object = __slab_alloc(s, gfpflags, node, addr, c);
-
- else {
+ if (unlikely(!object)) {
+ local_irq_restore(flags);
+ goto out;
+ }
+ } else {
object = c->freelist;
c->freelist = object[c->offset];
}
local_irq_restore(flags);

- if (unlikely((gfpflags & __GFP_ZERO) && object))
+ if (unlikely((gfpflags & __GFP_ZERO)))
memset(object, 0, c->objsize);
-
+out:
return object;
}

--