From: Dave Hansen <dave@sr71.net>
To: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com,
Dave Hansen <dave@sr71.net>
Subject: [RFC][PATCH] mm: percpu pages: up batch size to fix arithmetic?? errror
Date: Wed, 11 Sep 2013 15:08:59 -0700 [thread overview]
Message-ID: <20130911220859.EB8204BB@viggo.jf.intel.com> (raw)
I really don't know where the:
batch /= 4; /* We effectively *= 4 below */
...
batch = rounddown_pow_of_two(batch + batch/2) - 1;
came from. The round down code at *MOST* does a *= 1.5, but
*averages* out to be just under 1.
On a system with 128GB in a zone, this means that we've got
(you can see in /proc/zoneinfo for yourself):
high: 186 (744kB)
batch: 31 (124kB)
That 124kB is almost precisely 1/4 of the "1/2 of a meg" that we
were shooting for. We're under-sizing the batches by about 4x.
This patch kills the /=4.
---
linux.git-davehans/mm/page_alloc.c | 1 -
1 file changed, 1 deletion(-)
diff -puN mm/page_alloc.c~debug-pcp-sizes-1 mm/page_alloc.c
--- linux.git/mm/page_alloc.c~debug-pcp-sizes-1 2013-09-11 14:41:08.532445664 -0700
+++ linux.git-davehans/mm/page_alloc.c 2013-09-11 15:03:47.403912683 -0700
@@ -4103,7 +4103,6 @@ static int __meminit zone_batchsize(stru
batch = zone->managed_pages / 1024;
if (batch * PAGE_SIZE > 512 * 1024)
batch = (512 * 1024) / PAGE_SIZE;
- batch /= 4; /* We effectively *= 4 below */
if (batch < 1)
batch = 1;
_
next reply other threads:[~2013-09-11 22:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-11 22:08 Dave Hansen [this message]
2013-09-11 23:08 ` [RFC][PATCH] mm: percpu pages: up batch size to fix arithmetic?? errror Cody P Schafer
2013-09-11 23:21 ` Cody P Schafer
2013-09-12 0:20 ` Dave Hansen
2013-09-12 14:16 ` Christoph Lameter
2013-09-12 15:21 ` Dave Hansen
2013-09-11 23:58 ` Dave Hansen
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