linux-kernel - Re: [PATCH 0/8] idle page tracking / working set estimation

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Message-ID: <CANN689G4Z21v6fcF1dt-10CpQp9V42_hGPcPP2d5FChfCon_9Q@mail.gmail.com>
Date:	Tue, 27 Sep 2011 03:14:09 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Balbir Singh <bsingharora@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Michael Wolf <mjwolf@...ibm.com>
Subject: Re: [PATCH 0/8] idle page tracking / working set estimation

On Tue, Sep 27, 2011 at 3:03 AM, Balbir Singh <bsingharora@...il.com> wrote:
> On Sat, Sep 17, 2011 at 9:09 AM, Michel Lespinasse <walken@...gle.com> wrote:
>> Patch 3 introduces page_referenced_kstaled(), which is similar to
>> page_referenced() but is used for idle page tracking rather than
>> for memory reclaimation. Since both functions clear the pte_young bits
>> and we don't want them to interfere with each other, two new page flags
>> are introduced that track when young pte references have been cleared by
>> each of the page_referenced variants.
>
> Sorry, I have trouble parsing this sentence, could you elaborate on "when"?

page_referenced() indicates if a page was accessed since the previous
page_referenced() call.

page_referenced_kstaled() indicates if a page was accessed since the
previous page_referenced_kstaled() call.

Both of the functions need to clear PTE young bits; however we don't
want the two functions to interfere with each other. To achieve this,
we add two page bits to indicate when a young PTE has been observed by
one of the functions but not by the other.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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