linux-kernel - Re: [PATCH] ksm: add vm_stat and meminfo entry to reflect pte mapping to ksm pages

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Message-Id: <20110301154100.212c4ff9.akpm@linux-foundation.org>
Date:	Tue, 1 Mar 2011 15:41:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	nai.xia@...il.com
Cc:	Izik Eidus <ieidus@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ksm: add vm_stat and meminfo entry to reflect pte
 mapping to ksm pages

On Sat, 26 Feb 2011 22:56:31 +0800
Nai Xia <nai.xia@...il.com> wrote:

> ksm_pages_sharing is updated by ksmd periodically.  In some cases, it cannot 
> reflect the actual savings and makes the benchmarks on volatile VMAs very 
> inaccurate.
> 
> This patch add a vm_stat entry and let the /proc/meminfo show information 
> about how much virutal address pte is being mapped to ksm pages.  With default 
> ksm paramters (pages_to_scan==100 && sleep_millisecs==20), this can result in 
> 50% more accurate averaged savings result for the following test program. 
> Bigger sleep_millisecs values will increase this deviation. 

So I think you're saying that the existing ksm_pages_sharing sysfs file
is no good.

You added a new entry to /proc/meminfo and left ksm_pages_sharing
as-is.  Why not leave /proc/meminfo alone, and fix up the existing
ksm_pages_sharing?

Also, the patch accumulates the NR_KSM_PAGES_SHARING counts on a
per-zone basis as well as on a global basis, but only provides the
global count to userspace.  The per-zone counts are potentially
interesting?  If not, maintaining the per-zone counters is wasted
overhead.

> 
> --- test.c-----
>

The "^---" token conventionally means "end of changelog".  Please avoid
inserting it into the middle of the changelog.

> +++ b/mm/ksm.c
> @@ -897,6 +897,7 @@ static int try_to_merge_one_page(struct vm_area_struct 
> *vma,

Your email client wordwraps the patches.
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