linux-kernel - Re: [PATCH 3/8] Allow huge page allocations to use GFP_HIGH

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Message-ID: <Pine.LNX.4.64.0701262038120.23091@skynet.skynet.ie>
Date:	Fri, 26 Jan 2007 20:44:40 +0000 (GMT)
From:	Mel Gorman <mel@....ul.ie>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Christoph Lameter <clameter@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] Allow huge page allocations to use GFP_HIGH_MOVABLE

On Fri, 26 Jan 2007, Chris Friesen wrote:

> Mel Gorman wrote:
>
>> Worse, the problem is to have high order contiguous blocks free at the time 
>> of allocation without reclaim or migration. If the allocations were not 
>> atomic, anti-fragmentation as it is today would be enough.
>
> Has anyone looked at marking the buffers as "needs refilling" then kick off a 
> kernel thread or something to do the allocations under GFP_KERNEL?

I haven't seen it being discussed although it's probably doable as an 
addition to the existing mempool mechanism. Anti-fragmentation would mean 
that the non-atomic GFP_KERNEL allocation had a chance of succeeding.

> That way we avoid having to allocate the buffers with GFP_ATOMIC.
>

Unless the load was so high that the pool was getting depleted and memory 
under so much pressure that reclaim could not keep up. But yes, it's 
possible that GFP_ATOMIC allocations could be avoided the majority of 
times.

> I seem to recall that the tulip driver used to do this.  Is it just too 
> complicated from a race condition standpoint?
>

It shouldn't be that complicated.

> We currently see this issue on our systems, as we have older e1000 hardware 
> with 9KB jumbo frames.  After a while we just fail to allocate buffers and 
> the system goes belly-up.
>

Can you describe a reliable way of triggering this problem? At best, I 
hear "on our undescribed workload, we sometimes see this problem" but not 
much in the way of details.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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