linux-kernel - Re: [RFC 1/2] deactive invalidated pages

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Date:	Tue, 23 Nov 2010 16:44:50 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>
Subject: Re: [RFC 1/2] deactive invalidated pages

On Tue, Nov 23, 2010 at 4:15 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 23 Nov 2010 15:05:39 +0900 Minchan Kim <minchan.kim@...il.com> wrote:
>
>> On Tue, Nov 23, 2010 at 2:48 PM, Andrew Morton
>> >> > move it to the head of the LRU anyway. __But given that the user has
>> >>
>> >> Why does it move into head of LRU?
>> >> If the page which isn't mapped doesn't have PG_referenced, it would be
>> >> reclaimed.
>> >
>> > If it's dirty or under writeback it can't be reclaimed!
>>
>> I see your point. And it's why I add it to head of inactive list.
>
> But that *guarantees* that the page will get a full trip around the
> inactive list.  And this will guarantee that potentially useful pages
> are reclaimed before the pages which we *know* the user doesn't want!
> Bad!
>
> Whereas if we queue it to the tail, it will only get that full trip if
> reclaim happens to run before the page is cleaned.  And we just agreed
> that reclaim isn't likely to run immediately, because pages are being
> freed.
>
> So we face a choice between guaranteed eviction of potentially-useful
> pages (which are very expensive to reestablish) versus a *possible*
> need to move an unreclaimable page to the head of the LRU, which is
> cheap.

How about flagging SetPageReclaim when we add it to head of inactive?
If page write is complete, end_page_writeback would move it to tail of
inactive.

-- 
Kind regards,
Minchan Kim
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