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

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Date:	Thu, 14 May 2009 08:58:25 -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:

> 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.

> So, we don't need deactivating anon pages in anon lru list.

If we are close to running out of swap space, with
swapins freeing up swap space on a regular basis,
I believe we do want to do aging on the active
pages, just so we can pick a decent page to swap
out next time swap space becomes available.

> +static int can_reclaim_anon(struct zone *zone, struct scan_control *sc)
> +{
> +	return (inactive_anon_is_low(zone, sc) && nr_swap_pages <= 0);
> +}
> +

This function name is misleading, because when we do have
swap space available but inactive_anon_is_low is false,
we still want to reclaim inactive anon pages!

What problem did you encounter that you think this patch
solves?

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