linux-kernel - Re: [PATCH 3/3] mm: page allocator: Reconsider zones for allocation after direct reclaim

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Message-ID: <4E27F2EC.2010902@jp.fujitsu.com>
Date:	Thu, 21 Jul 2011 18:35:40 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	mgorman@...e.de
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: page allocator: Reconsider zones for allocation
 after direct reclaim

Hi





>> So, I think we don't need to care zonelist, just kswapd turn off
>> their own node.
> 
> I don't understand what you mean by this.

This was the answer of following your comments.

> Instead, couldn't we turn zlc->fullzones off from kswapd?
> >
> > Which zonelist should it clear (there are two)

I mean, buddy list is belong to zone, not zonelist. therefore, kswapd
don't need to look up zonelist.

So, I'd suggest either following way,
 - use direct reclaim path, but only clear a zlc bit of zones in reclaimed zonelist, not all. or
 - use kswapd and only clear a zlc bit at kswap exiting balance_pgdat

I'm prefer to add a branch to slowpath (ie reclaim path) rather than fast path.


>> And, just curious, If we will have a proper zlc clear point, why
>> do we need to keep HZ timeout?
> 
> Yes because we are not guaranteed to call direct reclaim either. Memory
> could be freed by a process exiting and I'd rather not add cost to
> the free path to find and clear all zonelists referencing the zone the
> page being freed belongs to.

Ok, it's good trade-off. I agree we need to keep HZ timeout.



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