linux-kernel - Re: [PATCH 02/10] mm: system wide ALLOC_NO

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Date:	Wed, 8 Aug 2007 11:09:06 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Daniel Phillips <daniel.raymond.phillips@...il.com>
cc:	Daniel Phillips <phillips@...nq.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>
Subject: Re: [PATCH 02/10] mm: system wide ALLOC_NO_WATERMARK

On Wed, 8 Aug 2007, Daniel Phillips wrote:

>   1. If the allocation can be satisified in the usual way, do that.
>   2. Otherwise, if the GFP flags do not include __GFP_MEMALLOC or
> PF_MEMALLOC is not set, fail the allocation
>   3. Otherwise, if the memcache's reserve quota is not reached,
> satisfy the request, allocating a new page from the MEMALLOC reserve,
> but the memcache's reserve counter and succeed

Maybe we need to kill PF_MEMALLOC....

> > Try NUMA constraints and zone limitations.
> 
> Are you worried about a correctness issue that would prevent the
> machine from operating, or are you just worried about allocating
> reserve pages to the local node for performance reasons?

I am worried that allocation constraints will make the approach incorrect. 
Because logically you must have distinct pools for each set of allocations 
constraints. Otherwise something will drain the precious reserve slab.

> > No I mean all 1024 processors of our system running into this fail/succeed
> > thingy that was added.
> 
> If an allocation now fails that would have succeeded in the past, the
> patch set is buggy.  I can't say for sure one way or another at this
> time of night.  If you see something, could you please mention a
> file/line number?

It seems that allocations fail that the reclaim logic should have taken 
care of letting succeed. Not good.
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