linux-kernel - Re: [RFC, PATCH] SLAB : [NUMA] keep nodeid in struct page instead of struct slab

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Date:	Wed, 21 Mar 2007 07:41:46 -0700 (PDT)
From:	Christoph Lameter <christoph@...eter.com>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCH] SLAB : [NUMA] keep nodeid in struct page instead
 of struct slab

On Wed, 21 Mar 2007, Eric Dumazet wrote:

> In order to avoid a cache miss in kmem_cache_free() on NUMA and reduce hot path length, we could exploit the following common facts.
> 
> 1) MAX_NUMNODES <= 64

MAX_NUMNODES == 1024 on IA64 and may be on x86_64 in the future.

> 2) alignment of 'struct kmem_cache *' can be >= 64
> 
> The following patch changes the page->lru.next to contain not only the 
> 'struct kmem_cache *' pointer, but also the nodeid in the low order 
> bits.

Nack.

I would suggest you audit slab and make sure that we never fall back and 
always enter a slab on the node of page_to_nid(page). If 
all allocations use GFP_THISNODE then you should be safe and then we can 
remove the nodeid from the slab structure and simply use the available 
node information in the page struct.
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