Date: Wed, 3 Nov 2010 23:10:47 -0400 (EDT)
From: caiqian@redhat.com
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>,
        Avi Kivity <avi@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>,
        Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>,
        Dave Hansen <dave@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Ingo Molnar <mingo@elte.hu>, Mike Travis <travis@sgi.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Christoph Lameter <cl@linux-foundation.org>,
        Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
        Chris Mason <chris.mason@oracle.com>, Borislav Petkov <bp@alien8.de>,
        linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
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There were some changes of behaviours with THP and KSM statistics demonstrated by this program, http://people.redhat.com/qcai/ksm01.c. 

There are 3 programs (A, B ,C) to allocate 128M memory each using KSM.
A has memory content = 'c'.
B has memory content = 'a'.
C has memory content = 'a'.
Then without THP,
pages_shared = 2
pages_sharing = 98285
pages_sharing = 98292
pages_unshared = 0
pages_volatile = 17
pages_to_scan = 98304
sleep_millisecs = 0
with THP,
pages_shared is 2.
pages_sharing is 18422.
pages_unshared is 0.
pages_volatile is 8.

Later,
A has memory content = 'c'
B has memory content = 'b'
C has memory content = 'a'.
Then without THP,
pages_shared = 3
pages_sharing = 98296
pages_unshared = 0
pages_volatile = 5
with THP,
pages_shared = 3
pages_sharing = 16358
pages_unshared = 0
pages_volatile = 23

Later,
A has memory content = 'd'
B has memory content = 'd'
C has memory content = 'd'
Then without THP,
pages_shared = 1
pages_sharing = 98274
pages_unshared = 0
pages_volatile = 29
with THP,
pages_shared = 1
pages_sharing = 8668
pages_unshared = 0
pages_volatile = 35

Finally,
A changes one page to 'e'
Then without THP,
pages_shared = 1
pages_sharing = 98274
pages_unshared = 1
pages_volatile = 28
with THP,
pages_shared = 1
pages_sharing = 8163
pages_unshared = 1
pages_volatile = 27

Are those differences for pages_sharing between with and without THP are expected?

CAI Qian
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