linux-kernel - Re: [RFC] SLAB : NUMA cache_free_alien() very expensive because of virt_to

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Message-ID: <Pine.LNX.4.64.0703201716440.17799@graphe.net>
Date:	Tue, 20 Mar 2007 17:18:04 -0700 (PDT)
From:	Christoph Lameter <christoph@...eter.com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Eric Dumazet <dada1@...mosbay.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] SLAB : NUMA cache_free_alien() very expensive because of
 virt_to_slab(objp); nodeid = slabp->nodeid;

On Tue, 20 Mar 2007, Andi Kleen wrote:

> > > Is it possible virt_to_slab(objp)->nodeid being different from pfn_to_nid(objp) ?
> > 
> > It is possible the page allocator falls back to another node than 
> > requested. We would need to check that this never occurs.
> 
> The only way to ensure that would be to set a strict mempolicy.
> But I'm not sure that's a good idea -- after all you don't want
> to fail an allocation in this case.
> 
> But pfn_to_nid on the object like proposed by Eric should work anyways.
> But I'm not sure the tables used for that will be more often cache hot
> than the slab.

We usually use page_to_nid(). Sure this will determine the node the object 
resides on. But this may not be the node on which the slab is tracked 
since there may have been a fallback at alloc time.

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