Re: [rfc 01/18] slub: Get rid of the node field

[Pekka Enberg <penberg@kernel.org>]

On Fri, Nov 11, 2011 at 10:07 PM, Christoph Lameter <cl@linux.com> wrote:
> The node field is always page_to_nid(c->page). So its rather easy to
> replace. Note that there will be additional overhead in various hot paths
> due to the need to mask a set of bits in page->flags and shift the
> result.
>
> Signed-off-by: Christoph Lameter <cl@linux.com>

This is a nice cleanup even if we never go irqless in the slowpaths.
Is page_to_nid() really that slow?

>
> ---
>  include/linux/slub_def.h |    1 -
>  mm/slub.c                |   15 ++++++---------
>  2 files changed, 6 insertions(+), 10 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c    2011-11-08 09:53:04.043865616 -0600
> +++ linux-2.6/mm/slub.c 2011-11-09 11:10:46.111334466 -0600
> @@ -1551,7 +1551,6 @@ static void *get_partial_node(struct kme
>
>                if (!object) {
>                        c->page = page;
> -                       c->node = page_to_nid(page);
>                        stat(s, ALLOC_FROM_PARTIAL);
>                        object = t;
>                        available =  page->objects - page->inuse;
> @@ -2016,7 +2015,7 @@ static void flush_all(struct kmem_cache
>  static inline int node_match(struct kmem_cache_cpu *c, int node)
>  {
>  #ifdef CONFIG_NUMA
> -       if (node != NUMA_NO_NODE && c->node != node)
> +       if (node != NUMA_NO_NODE && page_to_nid(c->page) != node)
>                return 0;
>  #endif
>        return 1;
> @@ -2105,7 +2104,6 @@ static inline void *new_slab_objects(str
>                page->freelist = NULL;
>
>                stat(s, ALLOC_SLAB);
> -               c->node = page_to_nid(page);
>                c->page = page;
>                *pc = c;
>        } else
> @@ -2202,7 +2200,6 @@ new_slab:
>        if (c->partial) {
>                c->page = c->partial;
>                c->partial = c->page->next;
> -               c->node = page_to_nid(c->page);
>                stat(s, CPU_PARTIAL_ALLOC);
>                c->freelist = NULL;
>                goto redo;
> @@ -2233,7 +2230,6 @@ new_slab:
>
>        c->freelist = get_freepointer(s, object);
>        deactivate_slab(s, c);
> -       c->node = NUMA_NO_NODE;
>        local_irq_restore(flags);
>        return object;
>  }
> @@ -4437,9 +4433,10 @@ static ssize_t show_slab_objects(struct
>                        struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
>                        struct page *page;
>
> -                       if (!c || c->node < 0)
> +                       if (!c || !c->page)
>                                continue;
>
> +                       node = page_to_nid(c->page);
>                        if (c->page) {
>                                        if (flags & SO_TOTAL)
>                                                x = c->page->objects;
> @@ -4449,16 +4446,16 @@ static ssize_t show_slab_objects(struct
>                                        x = 1;
>
>                                total += x;
> -                               nodes[c->node] += x;
> +                               nodes[node] += x;
>                        }
>                        page = c->partial;
>
>                        if (page) {
>                                x = page->pobjects;
>                                 total += x;
> -                                nodes[c->node] += x;
> +                                nodes[node] += x;
>                        }
> -                       per_cpu[c->node]++;
> +                       per_cpu[node]++;
>                }
>        }
>
> Index: linux-2.6/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slub_def.h     2011-11-08 09:53:03.979865196 -0600
> +++ linux-2.6/include/linux/slub_def.h  2011-11-09 11:10:46.121334523 -0600
> @@ -45,7 +45,6 @@ struct kmem_cache_cpu {
>        unsigned long tid;      /* Globally unique transaction id */
>        struct page *page;      /* The slab from which we are allocating */
>        struct page *partial;   /* Partially allocated frozen slabs */
> -       int node;               /* The node of the page (or -1 for debug) */
>  #ifdef CONFIG_SLUB_STATS
>        unsigned stat[NR_SLUB_STAT_ITEMS];
>  #endif
>
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