Re: [PATCH 3/5] mm: slub allocation fairness

Christoph Lameter
2007-05-14T15:49:37Z

On Mon, 14 May 2007, Peter Zijlstra wrote:

> Index: linux-2.6-git/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6-git.orig/include/linux/slub_def.h
> +++ linux-2.6-git/include/linux/slub_def.h
> @@ -52,6 +52,7 @@ struct kmem_cache {
> struct kmem_cache_node *node[MAX_NUMNODES];
> #endif
> struct page *cpu_slab[NR_CPUS];
> + int rank;
> };

Ranks as part of the kmem_cache structure? I thought this is a temporary
thing?

> * Lock order:
> @@ -961,6 +962,8 @@ static struct page *allocate_slab(struct
> if (!page)
> return NULL;
>
> + s->rank = page->index;
> +

Argh.... Setting a cache structure field from a page struct field? What
about concurrency?

> @@ -1371,8 +1376,12 @@ static void *__slab_alloc(struct kmem_ca
> gfp_t gfpflags, int node, void *addr, struct page *page)
> {
> void **object;
> - int cpu = smp_processor_id();
> + int cpu;
> +
> + if (page == FORCE_PAGE)
> + goto force_new;
>
> + cpu = smp_processor_id();
> if (!page)
> goto new_slab;
>
> @@ -1405,6 +1414,7 @@ have_slab:
> goto load_freelist;
> }
>
> +force_new:
> page = new_slab(s, gfpflags, node);
> if (page) {
> cpu = smp_processor_id();
> @@ -1465,15 +1475,22 @@ static void __always_inline *slab_alloc(
> struct page *page;
> void **object;
> unsigned long flags;
> + int rank = slab_alloc_rank(gfpflags);
>
> local_irq_save(flags);
> + if (slab_insufficient_rank(s, rank)) {
> + page = FORCE_PAGE;
> + goto force_alloc;
> + }
> +
> page = s->cpu_slab[smp_processor_id()];
> if (unlikely(!page || !page->lockless_freelist ||
> - (node != -1 && page_to_nid(page) != node)))
> + (node != -1 && page_to_nid(page) != node))) {
>
> +force_alloc:
> object = __slab_alloc(s, gfpflags, node, addr, page);
>
> - else {
> + } else {
> object = page->lockless_freelist;
> page->lockless_freelist = object[page->offset];
> }

This is the hot path. No modifications please.