linux-kernel - Re: [PATCH v5 5/7] mm: rework reclaim

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Date:	Fri, 9 Mar 2012 10:32:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <jweiner@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/7] mm: rework reclaim_stat counters

On Thu, 08 Mar 2012 22:04:19 +0400
Konstantin Khlebnikov <khlebnikov@...nvz.org> wrote:

> Currently there is two types of reclaim-stat counters:
> recent_scanned (pages picked from from lru),
> recent_rotated (pages putted back to active lru).
> Reclaimer uses ratio recent_rotated / recent_scanned
> for balancing pressure between file and anon pages.
> 
> But if we pick page from lru we can either reclaim it or put it back to lru, thus:
> recent_scanned == recent_rotated[inactive] + recent_rotated[active] + reclaimed
> This can be called "The Law of Conservation of Memory" =)
> 
> Thus recent_rotated counters for each lru list is enough, reclaimed pages can be
> counted as rotatation into inactive lru. After that reclaimer can use this ratio:
> recent_rotated[active] / (recent_rotated[active] + recent_rotated[inactive])
> 
> After this patch struct zone_reclaimer_stat has only one array: recent_rotated,
> which is directly indexed by lru list index:
> 
> before patch:
> 
> LRU_ACTIVE_ANON   -> LRU_ACTIVE_ANON   : recent_scanned[ANON]++, recent_rotated[ANON]++
> LRU_INACTIVE_ANON -> LRU_ACTIVE_ANON   : recent_scanned[ANON]++, recent_rotated[ANON]++
> LRU_ACTIVE_ANON   -> LRU_INACTIVE_ANON : recent_scanned[ANON]++
> LRU_INACTIVE_ANON -> LRU_INACTIVE_ANON : recent_scanned[ANON]++
> 
> after patch:
> 
> LRU_ACTIVE_ANON   -> LRU_ACTIVE_ANON   : recent_rotated[LRU_ACTIVE_ANON]++
> LRU_INACTIVE_ANON -> LRU_ACTIVE_ANON   : recent_rotated[LRU_ACTIVE_ANON]++
> LRU_ACTIVE_ANON   -> LRU_INACTIVE_ANON : recent_rotated[LRU_INACTIVE_ANON]++
> LRU_INACTIVE_ANON -> LRU_INACTIVE_ANON : recent_rotated[LRU_INACTIVE_ANON]++
> 
> recent_scanned[ANON] === recent_rotated[LRU_ACTIVE_ANON] + recent_rotated[LRU_INACTIVE_ANON]
> recent_rotated[ANON] === recent_rotated[LRU_ACTIVE_ANON]
> 
> (and the same for FILE/LRU_ACTIVE_FILE/LRU_INACTIVE_FILE)
> 
> v5:
> * resolve conflict with "memcg: fix GPF when cgroup removal races with last exit"
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>

Nice description.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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