linux-kernel - Re: [PATCH 4/4] mm: vmscan: Only read new_classzone_idx from pgdat when reclaiming successfully

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Message-ID: <20110719160903.GA2978@barrios-desktop>
Date:	Wed, 20 Jul 2011 01:09:03 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pádraig Brady <P@...igBrady.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Colin King <colin.king@...onical.com>,
	Andrew Lutomirski <luto@....edu>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] mm: vmscan: Only read new_classzone_idx from pgdat
 when reclaiming successfully

Hi Mel,

Too late review.
At that time, I had no time to look into this patch.

On Fri, Jun 24, 2011 at 03:44:57PM +0100, Mel Gorman wrote:
> During allocator-intensive workloads, kswapd will be woken frequently
> causing free memory to oscillate between the high and min watermark.
> This is expected behaviour.  Unfortunately, if the highest zone is
> small, a problem occurs.
> 
> When balance_pgdat() returns, it may be at a lower classzone_idx than
> it started because the highest zone was unreclaimable. Before checking

Yes.

> if it should go to sleep though, it checks pgdat->classzone_idx which
> when there is no other activity will be MAX_NR_ZONES-1. It interprets

Yes.

> this as it has been woken up while reclaiming, skips scheduling and

Hmm. I can't understand this part.
If balance_pgdat returns lower classzone and there is no other activity,
new_classzone_idx is always MAX_NR_ZONES - 1 so that classzone_idx would be less than
new_classzone_idx. It means it doesn't skip scheduling.

Do I miss something?

-- 
Kinds regards,
Minchan Kim
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