From: Benjamin LaHaise <bcrl@linux.intel.com>
To: akpm@osdl.org
Cc: linux-mm@kvack.org
Subject: [PATCH] use 32 bit division in slab_put_obj()
Date: Fri, 20 Jan 2006 17:12:46 -0800 [thread overview]
Message-ID: <20060121011245.GA24301@linux.intel.com> (raw)
The patch below improves the performance of slab_put_obj(). Without the
cast, gcc considers ptrdiff_t a 64 bit signed integer and ends up emitting
code to use a full signed 128 bit divide on EM64T, which is substantially
slower than a 32 bit unsigned divide. I noticed this when looking at the
profile of a case where the slab balance is just on edge and thrashes back
and forth freeing a block.
Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@intel.com>
diff -X work-2.6.16-rc1-mm2/Documentation/dontdiff -urP /home/bcrl/kernels/v2.6/linux-2.6.16-rc1-mm2/mm/slab.c work-2.6.16-rc1-mm2/mm/slab.c
--- /home/bcrl/kernels/v2.6/linux-2.6.16-rc1-mm2/mm/slab.c 2006-01-20 15:20:16.000000000 -0500
+++ work-2.6.16-rc1-mm2/mm/slab.c 2006-01-20 16:41:59.000000000 -0500
@@ -2267,8 +2267,12 @@
static void slab_put_obj(struct kmem_cache *cachep, struct slab *slabp, void *objp,
int nodeid)
{
- unsigned int objnr = (objp - slabp->s_mem) / cachep->buffer_size;
+ /* Slabs are always <4GB in size, so use a less expensive division. */
+ unsigned objnr = (unsigned)(objp - slabp->s_mem) / cachep->buffer_size;
+#if DEBUG
+ WARN_ON((unsigned long)(objp - slabp->s_mem) > ~0U);
+#endif
#if 0
/* Verify that the slab belongs to the intended node */
WARN_ON(slabp->nodeid != nodeid);
--
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next reply other threads:[~2006-01-21 1:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-21 1:12 Benjamin LaHaise [this message]
2006-01-23 6:39 ` Andrew Morton
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