linux-kernel - Re: [PATCH 6/9] ksm: mem cgroup charge swapin copy

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Message-ID: <20091125142355.GD2970@balbir.in.ibm.com>
Date:	Wed, 25 Nov 2009 19:53:55 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 6/9] ksm: mem cgroup charge swapin copy

* Hugh Dickins <hugh.dickins@...cali.co.uk> [2009-11-24 16:51:13]:

> But ksm swapping does require one small change in mem cgroup handling.
> When do_swap_page()'s call to ksm_might_need_to_copy() does indeed
> substitute a duplicate page to accommodate a different anon_vma (or a
> different index), that page escaped mem cgroup accounting, because of
> the !PageSwapCache check in mem_cgroup_try_charge_swapin().
> 

The duplicate page doesn't show up as PageSwapCache or are we optimizing
for the race condition where the page is not in SwapCache? I should
probably look at the full series.

> That was returning success without charging, on the assumption that
> pte_same() would fail after, which is not the case here.  Originally I
> proposed that success, so that an unshrinkable mem cgroup at its limit
> would not fail unnecessarily; but that's a minor point, and there are
> plenty of other places where we may fail an overallocation which might
> later prove unnecessary.  So just go ahead and do what all the other
> exceptions do: proceed to charge current mm.
> 
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>


Thanks for the patch!
Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
 
-- 
	Balbir
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