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

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Message-ID: <20070320213218.GA13952@one.firstfloor.org>
Date:	Tue, 20 Mar 2007 22:32:18 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <christoph@...eter.com>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.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;

> > 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.

-Andi
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