linux-kernel - [PATCH] SLAB : Use num_possible_cpus() in enable

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Date:	Wed, 21 Mar 2007 07:57:26 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Christoph Lameter <christoph@...eter.com>,
	Andi Kleen <andi@...stfloor.org>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] SLAB : Use num_possible_cpus() in enable_cpucache()

The existing comment in mm/slab.c is *perfect*, so I reproduce it :

         /*
          * CPU bound tasks (e.g. network routing) can exhibit cpu bound
          * allocation behaviour: Most allocs on one cpu, most free operations
          * on another cpu. For these cases, an efficient object passing between
          * cpus is necessary. This is provided by a shared array. The array
          * replaces Bonwick's magazine layer.
          * On uniprocessor, it's functionally equivalent (but less efficient)
          * to a larger limit. Thus disabled by default.
          */

As most shiped linux kernels are now compiled with CONFIG_SMP, there is no way 
a preprocessor #if can detect if the machine is UP or SMP. Better to use 
num_possible_cpus().

This means on UP we allocate a 'size=0 shared array', to be more efficient.

Another patch can later avoid the allocations of 'empty shared arrays', to 
save some memory.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

View attachment "slab_use_num_possible_cpus.patch" of type "text/plain" (399 bytes)