Re: [PATCH 3/3] mm/slub: wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL

[Wei Yang <richard.weiyang@gmail.com>]

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On Sun, Apr 30, 2017 at 07:31:52PM +0800, Wei Yang wrote:
>kmem_cache->cpu_partial is just used when CONFIG_SLUB_CPU_PARTIAL is set,
>so wrap it with config CONFIG_SLUB_CPU_PARTIAL will save some space
>on 32bit arch.
>
>This patch wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL
>and wrap its sysfs too.
>
>Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>---
> include/linux/slub_def.h |  2 ++
> mm/slub.c                | 72 +++++++++++++++++++++++++++++-------------------
> 2 files changed, 46 insertions(+), 28 deletions(-)
>
>diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
>index 0debd8df1a7d..477ab99800ed 100644
>--- a/include/linux/slub_def.h
>+++ b/include/linux/slub_def.h
>@@ -69,7 +69,9 @@ struct kmem_cache {
> 	int size;		/* The size of an object including meta data */
> 	int object_size;	/* The size of an object without meta data */
> 	int offset;		/* Free pointer offset. */
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	int cpu_partial;	/* Number of per cpu partial objects to keep around */
>+#endif
> 	struct kmem_cache_order_objects oo;
> 
> 	/* Allocation and freeing of slabs */
>diff --git a/mm/slub.c b/mm/slub.c
>index fde499b6dad8..94978f27882a 100644
>--- a/mm/slub.c
>+++ b/mm/slub.c
>@@ -1829,7 +1829,10 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
> 			stat(s, CPU_PARTIAL_NODE);
> 		}
> 		if (!kmem_cache_has_cpu_partial(s)
>-			|| available > s->cpu_partial / 2)
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
>+			|| available > s->cpu_partial / 2
>+#endif
>+			)
> 			break;

Matthew,

I plan to change this one with the same idea you mentioned in previous reply.

While one special "technique" is how to name it.

How about name this one

    slub_cpu_partial()

And rename the previous one

   slub_percpu_partial()

This is really hard to say which one is better :-(
Not sure whether you have some insight in this.

> 
> 	}
>@@ -3418,6 +3421,39 @@ static void set_min_partial(struct kmem_cache *s, unsigned long min)
> 	s->min_partial = min;
> }
> 
>+static void set_cpu_partial(struct kmem_cache *s)
>+{
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
>+	/*
>+	 * cpu_partial determined the maximum number of objects kept in the
>+	 * per cpu partial lists of a processor.
>+	 *
>+	 * Per cpu partial lists mainly contain slabs that just have one
>+	 * object freed. If they are used for allocation then they can be
>+	 * filled up again with minimal effort. The slab will never hit the
>+	 * per node partial lists and therefore no locking will be required.
>+	 *
>+	 * This setting also determines
>+	 *
>+	 * A) The number of objects from per cpu partial slabs dumped to the
>+	 *    per node list when we reach the limit.
>+	 * B) The number of objects in cpu partial slabs to extract from the
>+	 *    per node list when we run out of per cpu objects. We only fetch
>+	 *    50% to keep some capacity around for frees.
>+	 */
>+	if (!kmem_cache_has_cpu_partial(s))
>+		s->cpu_partial = 0;
>+	else if (s->size >= PAGE_SIZE)
>+		s->cpu_partial = 2;
>+	else if (s->size >= 1024)
>+		s->cpu_partial = 6;
>+	else if (s->size >= 256)
>+		s->cpu_partial = 13;
>+	else
>+		s->cpu_partial = 30;
>+#endif
>+}
>+
> /*
>  * calculate_sizes() determines the order and the distribution of data within
>  * a slab object.
>@@ -3576,33 +3612,7 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags)
> 	 */
> 	set_min_partial(s, ilog2(s->size) / 2);
> 
>-	/*
>-	 * cpu_partial determined the maximum number of objects kept in the
>-	 * per cpu partial lists of a processor.
>-	 *
>-	 * Per cpu partial lists mainly contain slabs that just have one
>-	 * object freed. If they are used for allocation then they can be
>-	 * filled up again with minimal effort. The slab will never hit the
>-	 * per node partial lists and therefore no locking will be required.
>-	 *
>-	 * This setting also determines
>-	 *
>-	 * A) The number of objects from per cpu partial slabs dumped to the
>-	 *    per node list when we reach the limit.
>-	 * B) The number of objects in cpu partial slabs to extract from the
>-	 *    per node list when we run out of per cpu objects. We only fetch
>-	 *    50% to keep some capacity around for frees.
>-	 */
>-	if (!kmem_cache_has_cpu_partial(s))
>-		s->cpu_partial = 0;
>-	else if (s->size >= PAGE_SIZE)
>-		s->cpu_partial = 2;
>-	else if (s->size >= 1024)
>-		s->cpu_partial = 6;
>-	else if (s->size >= 256)
>-		s->cpu_partial = 13;
>-	else
>-		s->cpu_partial = 30;
>+	set_cpu_partial(s);
> 
> #ifdef CONFIG_NUMA
> 	s->remote_node_defrag_ratio = 1000;
>@@ -3989,7 +3999,9 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
> 	 * Disable empty slabs caching. Used to avoid pinning offline
> 	 * memory cgroups by kmem pages that can be freed.
> 	 */
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	s->cpu_partial = 0;
>+#endif
> 	s->min_partial = 0;
> 
> 	/*
>@@ -4929,6 +4941,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
> }
> SLAB_ATTR(min_partial);
> 
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> static ssize_t cpu_partial_show(struct kmem_cache *s, char *buf)
> {
> 	return sprintf(buf, "%u\n", s->cpu_partial);
>@@ -4951,6 +4964,7 @@ static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
> 	return length;
> }
> SLAB_ATTR(cpu_partial);
>+#endif
> 
> static ssize_t ctor_show(struct kmem_cache *s, char *buf)
> {
>@@ -5363,7 +5377,9 @@ static struct attribute *slab_attrs[] = {
> 	&objs_per_slab_attr.attr,
> 	&order_attr.attr,
> 	&min_partial_attr.attr,
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	&cpu_partial_attr.attr,
>+#endif
> 	&objects_attr.attr,
> 	&objects_partial_attr.attr,
> 	&partial_attr.attr,
>-- 
>2.11.0

-- 
Wei Yang
Help you, Help me

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