linux-kernel - Re: [PATCH 6/6] mm: kswapd: Use the classzone idx that kswapd was using for sleeping

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Message-ID: <AANLkTi=4sGZjUqWm4RKs6mgQVma26FeAGUK2zOPVL2oV@mail.gmail.com>
Date:	Fri, 10 Dec 2010 11:38:23 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Simon Kirby <sim@...tway.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] mm: kswapd: Use the classzone idx that kswapd was
 using for sleeping_prematurely()

On Thu, Dec 9, 2010 at 8:18 PM, Mel Gorman <mel@....ul.ie> wrote:
> When kswapd is woken up for a high-order allocation, it takes account of
> the highest usable zone by the caller (the classzone idx). During
> allocation, this index is used to select the lowmem_reserve[] that
> should be applied to the watermark calculation in zone_watermark_ok().
>
> When balancing a node, kswapd considers the highest unbalanced zone to be the
> classzone index. This will always be at least be the callers classzone_idx
> and can be higher. However, sleeping_prematurely() always considers the
> lowest zone (e.g. ZONE_DMA) to be the classzone index. This means that
> sleeping_prematurely() can consider a zone to be balanced that is unusable
> by the allocation request that originally woke kswapd. This patch changes
> sleeping_prematurely() to use a classzone_idx matching the value it used
> in balance_pgdat().
>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

Nice catch! and it does make sense to me.

-- 
Kind regards,
Minchan Kim
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