linux-kernel - Re: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru

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Date:	Fri, 16 Jul 2010 10:44:24 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru_pages, 
	not page order

On Fri, Jul 16, 2010 at 10:39 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> >     nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
>> >     if (nr_slab_pages0 > zone->min_slab_pages) {
>> > +           unsigned long lru_pages = zone_reclaimable_pages(zone);
>> > +
>> >             /*
>> >              * shrink_slab() does not currently allow us to determine how
>> >              * many pages were freed in this zone. So we take the current
>> > @@ -2622,7 +2624,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
>> >              * Note that shrink_slab will free memory on all zones and may
>> >              * take a long time.
>> >              */
>> > -           while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
>> > +           while (shrink_slab(sc.nr_scanned, gfp_mask, lru_pages) &&
>> >                    (zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages >
>> >                     nr_slab_pages0))
>> >                     ;
>>
>> Wouldn't it be better to recalculate zone_reclaimable_pages() each time
>> around the loop?  For example, shrink_icache_memory()->prune_icache()
>> will remove pagecache from an inode if it hits the tail of the list.
>> This can change the number of reclaimable pages by squigabytes, but
>> this code thinks nothing changed?
>
> Ah, I missed this. incrementa patch is here.
>
> thank you!
>
>
>
> From 8f7c70cfb4a25f8292a59564db6c3ff425a69b53 Mon Sep 17 00:00:00 2001
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Date: Fri, 16 Jul 2010 08:40:01 +0900
> Subject: [PATCH] vmscan: recalculate lru_pages on each shrink_slab()
>
> Andrew Morton pointed out shrink_slab() may change number of reclaimable
> pages (e.g. shrink_icache_memory()->prune_icache() will remove unmapped
> pagecache).
>
> So, we need to recalculate lru_pages on each shrink_slab() calling.
> This patch fixes it.
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

It does make sense.

-- 
Kind regards,
Minchan Kim
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