Messages in this thread Patch in this message |  | | | Date | Wed, 21 Mar 2007 07:57:26 +0100 | | From | Eric Dumazet <> | | Subject | [PATCH] SLAB : Use num_possible_cpus() in enable_cpucache() |
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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@cosmosbay.com> diff --git a/mm/slab.c b/mm/slab.c index 57f7aa4..a69d0a5 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3975,10 +3975,8 @@ static int enable_cpucache(struct kmem_c * to a larger limit. Thus disabled by default. */ shared = 0; -#ifdef CONFIG_SMP - if (cachep->buffer_size <= PAGE_SIZE) + if (cachep->buffer_size <= PAGE_SIZE && num_possible_cpus() > 1) shared = 8; -#endif #if DEBUG /* |  |