linux-kernel - Re: [PATCH] vmscan: zone_reclaim don't call disable_swap

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Message-Id: <20100628103508.3870.A69D9226@jp.fujitsu.com>
Date:	Mon, 28 Jun 2010 10:37:47 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] vmscan: zone_reclaim don't call disable_swap_token()

> On Fri, Jun 25, 2010 at 5:31 PM, KOSAKI Motohiro
> <kosaki.motohiro@...fujitsu.com> wrote:
> > Swap token don't works when zone reclaim is enabled since it was born.
> > Because __zone_reclaim() always call disable_swap_token()
> > unconditionally.
> >
> > This kill swap token feature completely. As far as I know, nobody want
> > to that. Remove it.
> >
> 
> In f7b7fd8f3ebbb, Rik added disable_swap_token.
> At that time, sc.priority in zone_reclaim is zero so it does make sense.
> But in a92f71263a, Christoph changed the priority to begin from
> ZONE_RECLAIM_PRIORITY with remained disable_swap_token. It doesn't
> make sense.
> 
> So doesn't we add disable_swap_token following as than removing?

f7b7fd8f3ebbb says disable_swap_token was introduced to prevent OOM.
but zone reclaim failure don't make OOM. instead, fallback to try_to_free_pages().

If the system have really heavy pressure, do_try_to_free_pages()
will call disable_swap_token().

So, What benefit is there?



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