linux-kernel - Re: 2.6.22 -mm merge plans: slub on PowerPC

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Date:	Thu, 3 May 2007 23:41:15 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Christoph Lameter <clameter@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: 2.6.22 -mm merge plans: slub on PowerPC

On Thu, 3 May 2007, Christoph Lameter wrote:
> 
> There are SLUB patches pending (not in rc7-mm2 as far as I can recall) 
> that reduce the default page order sizes to head off this issue. The 
> defaults were initially too large (and they still default to large
> for testing if Mel's Antifrag work is detected to be active).

Sounds good.

> > -	return kmem_cache_alloc(pgtable_cache[PTE_CACHE_NUM],
> > -				GFP_KERNEL|__GFP_REPEAT);
> > +	return quicklist_alloc(0, GFP_KERNEL|__GFP_REPEAT, NULL);
> 
> __GFP_REPEAT is unusual here but this was carried over from the 
> kmem_cache_alloc it seems. Hmm... There is some variance on how we do this 
> between arches. Should we uniformly set or not set this flag?

Not something to get into in this patch, but it did surprise me too.
I believe __GFP_REPEAT should be avoided, and I don't see justification
for it here (but need to remember not to do a blind virt_to_page on the
result in some places if it might return NULL - which IIRC it actually
can do even if __GFP_REPEAT, when chosen for OOM kill).  But I've a
suspicion it got put in there for some good reason I don't know about.

Hugh
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