Re: [patch 07/23] SLUB: Add defrag_ratio field and sysfs support.

Mel Gorman
2007-11-08T15:07:22Z

On (06/11/07 17:11), Christoph Lameter didst pronounce:
> The defrag_ratio is used to set the threshold at which defragmentation
> should be run on a slabcache.
>

I'm thick, I would like to see a quick note here on what defragmentation
means. Also, this defrag_ratio seems to have a significantly different
meaning to the other defrag_ratio which isn't helping my poor head at
all.

"The defrag_ratio sets a threshold at which a slab will be vacated of all
it's objects and the pages freed during memory reclaim."

?

> The allocation ratio is measured in a percentage of the available slots.
> The percentage will be lower for slabs that are more fragmented.
>
> Add a defrag ratio field and set it to 30% by default. A limit of 30% specified
> that less than 3 out of 10 available slots for objects are in use before
> reclaim occurs.
>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> ---
> include/linux/slub_def.h | 7 +++++++
> mm/slub.c | 18 ++++++++++++++++++
> 2 files changed, 25 insertions(+)
>
> Index: linux-2.6/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slub_def.h 2007-11-06 12:36:28.000000000 -0800
> +++ linux-2.6/include/linux/slub_def.h 2007-11-06 12:37:44.000000000 -0800
> @@ -53,6 +53,13 @@ struct kmem_cache {
> void (*ctor)(struct kmem_cache *, void *);
> int inuse; /* Offset to metadata */
> int align; /* Alignment */
> + int defrag_ratio; /*
> + * objects/possible-objects limit. If we have
> + * less that the specified percentage of
> + * objects allocated then defrag passes
> + * will start to occur during reclaim.
> + */
> +
> const char *name; /* Name (only for display!) */
> struct list_head list; /* List of slab caches */
> #ifdef CONFIG_SLUB_DEBUG
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2007-11-06 12:37:25.000000000 -0800
> +++ linux-2.6/mm/slub.c 2007-11-06 12:37:44.000000000 -0800
> @@ -2363,6 +2363,7 @@ static int kmem_cache_open(struct kmem_c
> goto error;
>
> s->refcount = 1;
> + s->defrag_ratio = 30;
> #ifdef CONFIG_NUMA
> s->remote_node_defrag_ratio = 100;
> #endif
> @@ -4005,6 +4006,22 @@ static ssize_t free_calls_show(struct km
> }
> SLAB_ATTR_RO(free_calls);
>
> +static ssize_t defrag_ratio_show(struct kmem_cache *s, char *buf)
> +{
> + return sprintf(buf, "%d\n", s->defrag_ratio);
> +}
> +
> +static ssize_t defrag_ratio_store(struct kmem_cache *s,
> + const char *buf, size_t length)
> +{
> + int n = simple_strtoul(buf, NULL, 10);
> +
> + if (n < 100)
> + s->defrag_ratio = n;
> + return length;
> +}
> +SLAB_ATTR(defrag_ratio);
> +
> #ifdef CONFIG_NUMA
> static ssize_t remote_node_defrag_ratio_show(struct kmem_cache *s, char *buf)
> {
> @@ -4047,6 +4064,7 @@ static struct attribute * slab_attrs[] =
> &shrink_attr.attr,
> &alloc_calls_attr.attr,
> &free_calls_attr.attr,
> + &defrag_ratio_attr.attr,
> #ifdef CONFIG_ZONE_DMA
> &cache_dma_attr.attr,
> #endif
>
> --
>

--
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab