[PATCH] mm: raise MemFree by reverting percpu_pagelist_fraction to0

From: Hugh Dickins
Date: Fri May 11 2012 - 04:00:25 EST

Why is there less MemFree than there used to be? It perturbed a test,
so I've just been bisecting linux-next, and now find the offender went
upstream yesterday.

Commit 93278814d359 "mm: fix division by 0 in percpu_pagelist_fraction()"
mistakenly initialized percpu_pagelist_fraction to the sysctl's minimum 8,
which leaves 1/8th of memory on percpu lists (on each cpu??); but most of
us expect it to be left unset at 0 (and it's not then used as a divisor).

MemTotal: 8061476kB 8061476kB 8061476kB 8061476kB 8061476kB 8061476kB
Repetitive test with percpu_pagelist_fraction 8:
MemFree: 6948420kB 6237172kB 6949696kB 6840692kB 6949048kB 6862984kB
Same test with percpu_pagelist_fraction back to 0:
MemFree: 7945000kB 7944908kB 7948568kB 7949060kB 7948796kB 7948812kB

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>

mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- 3.4-rc6+/mm/page_alloc.c 2012-05-10 22:53:35.362478419 -0700
+++ linux/mm/page_alloc.c 2012-05-11 00:07:31.613657283 -0700
@@ -105,7 +105,7 @@ unsigned long totalreserve_pages __read_
unsigned long dirty_balance_reserve __read_mostly;

-int percpu_pagelist_fraction = 8;
+int percpu_pagelist_fraction;
gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;

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