linux-kernel - Re: [PATCH]mmap: add alignment for some variables

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Message-ID: <1301360054.3981.31.camel@sli10-conroe>
Date:	Tue, 29 Mar 2011 08:54:14 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH]mmap: add alignment for some variables

On Tue, 2011-03-29 at 00:55 +0800, Andi Kleen wrote:
> Shaohua Li <shaohua.li@...el.com> writes:
> 
> > Make some variables have correct alignment.
> 
> Nit: __read_mostly doesn't change alignment, just the section.
> Please fix the description. Other than that it looks good.
sure.

Make some variables have correct alignment/section to avoid cache issue.
In a workload which heavily does mmap/munmap, the variables will be used
frequently.

Signed-off-by: Shaohua Li <shaohua.li@...el.com>
---
 mm/mmap.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux/mm/mmap.c
===================================================================
--- linux.orig/mm/mmap.c	2011-03-29 08:30:12.000000000 +0800
+++ linux/mm/mmap.c	2011-03-29 08:30:54.000000000 +0800
@@ -84,10 +84,10 @@ pgprot_t vm_get_page_prot(unsigned long
 }
 EXPORT_SYMBOL(vm_get_page_prot);
 
-int sysctl_overcommit_memory = OVERCOMMIT_GUESS;  /* heuristic overcommit */
-int sysctl_overcommit_ratio = 50;	/* default is 50% */
+int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;  /* heuristic overcommit */
+int sysctl_overcommit_ratio __read_mostly = 50;	/* default is 50% */
 int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
-struct percpu_counter vm_committed_as;
+struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp;
 
 /*
  * Check that a process has enough memory to allocate a new virtual


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