linux-kernel - Re: [RFC/PATCH] SLUB: Optimize slab

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Date:	Sat, 2 Oct 2010 18:03:25 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC/PATCH] SLUB: Optimize slab_free() debug check

On Sat, 2 Oct 2010, Pekka Enberg wrote:

> This patch optimizes slab_free() debug check to use "c->node != NUMA_NO_NODE"
> instead of "c->node >= 0" because the former generates smaller code on x86-64:
> 
>   Before:
> 
>     4736:       48 39 70 08             cmp    %rsi,0x8(%rax)
>     473a:       75 26                   jne    4762 <kfree+0xa2>
>     473c:       44 8b 48 10             mov    0x10(%rax),%r9d
>     4740:       45 85 c9                test   %r9d,%r9d
>     4743:       78 1d                   js     4762 <kfree+0xa2>
> 
>   After:
> 
>     4736:       48 39 70 08             cmp    %rsi,0x8(%rax)
>     473a:       75 23                   jne    475f <kfree+0x9f>
>     473c:       83 78 10 ff             cmpl   $0xffffffffffffffff,0x10(%rax)
>     4740:       74 1d                   je     475f <kfree+0x9f>
> 
> This patch also cleans up __slab_alloc() to use NUMA_NO_NODE instead of "-1"
> for enabling debugging for a per-CPU cache.
> 
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Pekka Enberg <penberg@...nel.org>

Acked-by: David Rientjes <rientjes@...gle.com>

You could compare to NUMA_NO_NODE in show_slab_objects(), as well, for the 
same optimization.
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