linux-kernel - Re: [PATCH] mmtom: Prevent shrinking of active anon lru list in case of no swap space V2

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Message-ID: <4A0C1A41.7040202@redhat.com>
Date:	Thu, 14 May 2009 09:18:57 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mmtom: Prevent shrinking of active anon lru list in case
 	of no swap space V2

Minchan Kim wrote:
> HI, Rik
> 
> Thanks for careful review. :)
> 
> On Thu, May 14, 2009 at 9:58 PM, Rik van Riel <riel@...hat.com> wrote:
>> Minchan Kim wrote:
>>
>>> Now shrink_active_list is called several places.
>>> But if we don't have a swap space, we can't reclaim anon pages.
>> If swap space has run out, get_scan_ratio() will return
>> 0 for the anon scan ratio, meaning we do not scan the
>> anon lists.
> 
> I think get_scan_ration can't prevent scanning of anon pages in no
> swap system(like embedded system).
> That's because in shrink_zone, you add following as
> 
>         /*
>          * Even if we did not try to evict anon pages at all, we want to
>          * rebalance the anon lru active/inactive ratio.
>          */
>         if (inactive_anon_is_low(zone, sc))
>                 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);

That's a fair point.

How about we change this to:

	if (inactive_anon_is_low(zone, sc) && nr_swap_pages >= 0)

That way GCC will statically optimize away this branch on
systems with CONFIG_SWAP=n.

Does that look reasonable?

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