linux-kernel - Re: [PATCH 3/7 v2] mm: rework __isolate_lru

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Date:	Sat, 10 Mar 2012 13:46:06 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Hugh Dickins <hughd@...gle.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7 v2] mm: rework __isolate_lru_page() file/anon filter

Konstantin Khlebnikov wrote:
> Hugh Dickins wrote:
>> On Fri, 9 Mar 2012, Konstantin Khlebnikov wrote:
>>>
>>> Actually __isolate_lru_page() even little bit bigger
>>
>> I was coming to realize that it must be your page_lru()ing:
>> although it's dressed up in one line, there's several branches there.
>
> Yes, but I think we can optimize page_lru(): we can prepare ready-to-use
> page lru index in lower bits of page->flags, if we swap page flags and split
> LRU_UNEVICTABLE into FILE/ANON parts.
>
>>
>> I think you'll find you have a clear winner at last, if you just pass
>> lru on down as third arg to __isolate_lru_page(), where file used to
>> be passed, instead of re-evaluating it inside.
>>
>> shrink callers already have the lru, and compaction works it out
>> immediately afterwards.
>
> No, for non-lumpy isolation we don't need this check at all,
> because all pages already picked from right lru list.
>
> I'll send separate patch for this (on top v5 patchset), after meditation =)

Heh, looks like we don't need these checks at all:
without RECLAIM_MODE_LUMPYRECLAIM we isolate only pages from right lru,
with RECLAIM_MODE_LUMPYRECLAIM we isolate pages from all evictable lru.
Thus we should check only PageUnevictable() on lumpy reclaim.

>
>>
>> Though we do need to be careful: the lumpy case would then have to
>> pass page_lru(cursor_page).  Oh, actually no (though it would deserve
>> a comment): since the lumpy case selects LRU_ALL_EVICTABLE, it's
>> irrelevant what it passes for lru, so might as well stick with
>> the one passed down.  Though you may decide I'm being too tricky
>> there, and prefer to calculate page_lru(cursor_page) anyway, it
>> not being the hottest path.
>>
>> Whether you'd still want page_lru(page) __always_inline, I don't know.
>>
>> Hugh
>
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