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Date: Tue, 07 Apr 2009 21:58:02 +0300
From: Pekka Enberg <penberg@...helsinki.fi>
To: David Rientjes <rientjes@...gle.com>
CC: Christoph Lameter <cl@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: [patch] slub: default min_partial to at least highest cpus per
node
Hi David,
David Rientjes wrote:
> The pre-defined MIN_PARTIAL value may not be suitable for machines with a
> large number of cpus per node. To avoid excessively allocating new slabs
> because there is not at least the same number of slabs on a node's
> partial list as cpus, this will default a cache's min_partial value to be
> at least the highest number of cpus per node on the system.
>
> This default will never exceed MAX_PARTIAL, however, so very large
> systems don't waste an excessive amount of memory.
>
> When remote_node_defrag_ratio allows defragmenting remote nodes, it
> ensures that nr_partial exceeds min_partial so there will always be a
> local reserve when a cpu slab is filled to avoid allocating new slabs
> locally as a result of a remote cpu stealing a partial slab.
>
> The cache's min_partial setting may still be changed by writing to
> /sys/kernel/slab/cache/min_partial. The only restriction when doing so
> is that the value be within MIN_PARTIAL and MAX_PARTIAL.
>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
Hmm, partial lists are per-node, so wouldn't it be better to do the
adjustment for every struct kmem_cache_node separately? The
'min_partial_per_node' global seems just too ugly and confusing to live
with.
Pekka
> ---
> mm/slub.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
> 1 files changed, 42 insertions(+), 8 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1941,6 +1941,15 @@ static unsigned long calculate_alignment(unsigned long flags,
> return ALIGN(align, sizeof(void *));
> }
>
> +static void set_min_partial(struct kmem_cache *s, unsigned long min)
> +{
> + if (min < MIN_PARTIAL)
> + min = MIN_PARTIAL;
> + else if (min > MAX_PARTIAL)
> + min = MAX_PARTIAL;
> + s->min_partial = min;
> +}
> +
> static void init_kmem_cache_cpu(struct kmem_cache *s,
> struct kmem_cache_cpu *c)
> {
> @@ -2093,6 +2102,8 @@ static inline int alloc_kmem_cache_cpus(struct kmem_cache *s, gfp_t flags)
> #endif
>
> #ifdef CONFIG_NUMA
> +static unsigned long min_partial_per_node;
> +
> /*
> * No kmalloc_node yet so do it by hand. We know that this is the first
> * slab on the node for this slabcache. There are no concurrent accesses
> @@ -2188,6 +2199,26 @@ static int init_kmem_cache_nodes(struct kmem_cache *s, gfp_t gfpflags)
> }
> return 1;
> }
> +
> +static void __cpuinit set_min_partial_per_node(int node)
> +{
> + unsigned int nr_cpus;
> +
> + /*
> + * Add one cpu since this is called for CPU_UP_PREPARE and this cpu is
> + * not online yet. CPU_ONLINE would require taking slub_lock.
> + */
> + nr_cpus = nr_cpus_node(node) + 1;
> + if (nr_cpus > min_partial_per_node)
> + min_partial_per_node = min_t(unsigned long,
> + nr_cpus, MAX_PARTIAL);
> +}
> +
> +static void set_cache_min_partial_per_node(struct kmem_cache *s)
> +{
> + if (s->min_partial < min_partial_per_node)
> + set_min_partial(s, min_partial_per_node);
> +}
> #else
> static void free_kmem_cache_nodes(struct kmem_cache *s)
> {
> @@ -2198,16 +2229,15 @@ static int init_kmem_cache_nodes(struct kmem_cache *s, gfp_t gfpflags)
> init_kmem_cache_node(&s->local_node, s);
> return 1;
> }
> -#endif
>
> -static void set_min_partial(struct kmem_cache *s, unsigned long min)
> +static inline void set_min_partial_per_node(int node)
> +{
> +}
> +
> +static inline void set_cache_min_partial_per_node(const struct kmem_cache *s)
> {
> - if (min < MIN_PARTIAL)
> - min = MIN_PARTIAL;
> - else if (min > MAX_PARTIAL)
> - min = MAX_PARTIAL;
> - s->min_partial = min;
> }
> +#endif
>
> /*
> * calculate_sizes() determines the order and the distribution of data within
> @@ -2352,6 +2382,7 @@ static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
> * list to avoid pounding the page allocator excessively.
> */
> set_min_partial(s, ilog2(s->size));
> + set_cache_min_partial_per_node(s);
> s->refcount = 1;
> #ifdef CONFIG_NUMA
> s->remote_node_defrag_ratio = 1000;
> @@ -3239,10 +3270,13 @@ static int __cpuinit slab_cpuup_callback(struct notifier_block *nfb,
> case CPU_UP_PREPARE:
> case CPU_UP_PREPARE_FROZEN:
> init_alloc_cpu_cpu(cpu);
> + set_min_partial_per_node(cpu_to_node(cpu));
> down_read(&slub_lock);
> - list_for_each_entry(s, &slab_caches, list)
> + list_for_each_entry(s, &slab_caches, list) {
> s->cpu_slab[cpu] = alloc_kmem_cache_cpu(s, cpu,
> GFP_KERNEL);
> + set_cache_min_partial_per_node(s);
> + }
> up_read(&slub_lock);
> break;
>
--
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