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    Subject[PATCH 04/29] mm: kmem_estimate_pages()
    Provide a method to get the upper bound on the pages needed to allocate
    a given number of objects from a given kmem_cache.

    This lays the foundation for a generic reserve framework as presented in
    a later patch in this series. This framework needs to convert object demand
    (kmalloc() bytes, kmem_cache_alloc() objects) to pages.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/slab.h | 3 +
    mm/slab.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++
    mm/slub.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 159 insertions(+)

    Index: linux-2.6/include/linux/slab.h
    ===================================================================
    --- linux-2.6.orig/include/linux/slab.h
    +++ linux-2.6/include/linux/slab.h
    @@ -60,6 +60,7 @@ void kmem_cache_free(struct kmem_cache *
    unsigned int kmem_cache_size(struct kmem_cache *);
    const char *kmem_cache_name(struct kmem_cache *);
    int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr);
    +unsigned kmem_estimate_pages(struct kmem_cache *cachep, gfp_t flags, int objects);

    /*
    * Please use this macro to create slab caches. Simply specify the
    @@ -94,6 +95,8 @@ int kmem_ptr_validate(struct kmem_cache
    void * __must_check krealloc(const void *, size_t, gfp_t);
    void kfree(const void *);
    size_t ksize(const void *);
    +unsigned kestimate_single(size_t, gfp_t, int);
    +unsigned kestimate(gfp_t, size_t);

    /*
    * Allocator specific definitions. These are mainly used to establish optimized
    Index: linux-2.6/mm/slub.c
    ===================================================================
    --- linux-2.6.orig/mm/slub.c
    +++ linux-2.6/mm/slub.c
    @@ -2446,6 +2446,37 @@ const char *kmem_cache_name(struct kmem_
    EXPORT_SYMBOL(kmem_cache_name);

    /*
    + * return the max number of pages required to allocated count
    + * objects from the given cache
    + */
    +unsigned kmem_estimate_pages(struct kmem_cache *s, gfp_t flags, int objects)
    +{
    + unsigned long slabs;
    +
    + if (WARN_ON(!s) || WARN_ON(!s->objects))
    + return 0;
    +
    + slabs = DIV_ROUND_UP(objects, s->objects);
    +
    + /*
    + * Account the possible additional overhead if the slab holds more that
    + * one object.
    + */
    + if (s->objects > 1) {
    + /*
    + * Account the possible additional overhead if per cpu slabs
    + * are currently empty and have to be allocated. This is very
    + * unlikely but a possible scenario immediately after
    + * kmem_cache_shrink.
    + */
    + slabs += num_online_cpus();
    + }
    +
    + return slabs << s->order;
    +}
    +EXPORT_SYMBOL_GPL(kmem_estimate_pages);
    +
    +/*
    * Attempt to free all slabs on a node. Return the number of slabs we
    * were unable to free.
    */
    @@ -2800,6 +2831,57 @@ static unsigned long count_partial(struc
    }

    /*
    + * return the max number of pages required to allocate @count objects
    + * of @size bytes from kmalloc given @flags.
    + */
    +unsigned kestimate_single(size_t size, gfp_t flags, int count)
    +{
    + struct kmem_cache *s = get_slab(size, flags);
    + if (!s)
    + return 0;
    +
    + return kmem_estimate_pages(s, flags, count);
    +
    +}
    +EXPORT_SYMBOL_GPL(kestimate_single);
    +
    +/*
    + * return the max number of pages required to allocate @bytes from kmalloc
    + * in an unspecified number of allocation of heterogeneous size.
    + */
    +unsigned kestimate(gfp_t flags, size_t bytes)
    +{
    + int i;
    + unsigned long pages;
    +
    + /*
    + * multiply by two, in order to account the worst case slack space
    + * due to the power-of-two allocation sizes.
    + */
    + pages = DIV_ROUND_UP(2 * bytes, PAGE_SIZE);
    +
    + /*
    + * add the kmem_cache overhead of each possible kmalloc cache
    + */
    + for (i = 1; i < PAGE_SHIFT; i++) {
    + struct kmem_cache *s;
    +
    +#ifdef CONFIG_ZONE_DMA
    + if (unlikely(flags & SLUB_DMA))
    + s = dma_kmalloc_cache(i, flags);
    + else
    +#endif
    + s = &kmalloc_caches[i];
    +
    + if (s)
    + pages += kmem_estimate_pages(s, flags, 0);
    + }
    +
    + return pages;
    +}
    +EXPORT_SYMBOL_GPL(kestimate);
    +
    +/*
    * kmem_cache_shrink removes empty slabs from the partial lists and sorts
    * the remaining slabs by the number of items in use. The slabs with the
    * most items in use come first. New allocations will then fill those up
    Index: linux-2.6/mm/slab.c
    ===================================================================
    --- linux-2.6.orig/mm/slab.c
    +++ linux-2.6/mm/slab.c
    @@ -3844,6 +3844,80 @@ const char *kmem_cache_name(struct kmem_
    EXPORT_SYMBOL_GPL(kmem_cache_name);

    /*
    + * return the max number of pages required to allocated count
    + * objects from the given cache
    + */
    +unsigned kmem_estimate_pages(struct kmem_cache *cachep, gfp_t flags, int objects)
    +{
    + /*
    + * (1) memory for objects,
    + */
    + unsigned nr_slabs = DIV_ROUND_UP(objects, cachep->num);
    + unsigned nr_pages = nr_slabs << cachep->gfporder;
    +
    + /*
    + * (2) memory for each per-cpu queue (nr_cpu_ids),
    + * (3) memory for each per-node alien queues (nr_cpu_ids), and
    + * (4) some amount of memory for the slab management structures
    + *
    + * XXX: truely account these
    + */
    + nr_pages += 1 + ilog2(nr_pages);
    +
    + return nr_pages;
    +}
    +
    +/*
    + * return the max number of pages required to allocate @count objects
    + * of @size bytes from kmalloc given @flags.
    + */
    +unsigned kestimate_single(size_t size, gfp_t flags, int count)
    +{
    + struct kmem_cache *s = kmem_find_general_cachep(size, flags);
    + if (!s)
    + return 0;
    +
    + return kmem_estimate_pages(s, flags, count);
    +}
    +EXPORT_SYMBOL_GPL(kestimate_single);
    +
    +/*
    + * return the max number of pages required to allocate @bytes from kmalloc
    + * in an unspecified number of allocation of heterogeneous size.
    + */
    +unsigned kestimate(gfp_t flags, size_t bytes)
    +{
    + unsigned long pages;
    + struct cache_sizes *csizep = malloc_sizes;
    +
    + /*
    + * multiply by two, in order to account the worst case slack space
    + * due to the power-of-two allocation sizes.
    + */
    + pages = DIV_ROUND_UP(2 * bytes, PAGE_SIZE);
    +
    + /*
    + * add the kmem_cache overhead of each possible kmalloc cache
    + */
    + for (csizep = malloc_sizes; csizep->cs_cachep; csizep++) {
    + struct kmem_cache *s;
    +
    +#ifdef CONFIG_ZONE_DMA
    + if (unlikely(flags & __GFP_DMA))
    + s = csizep->cs_dmacachep;
    + else
    +#endif
    + s = csizep->cs_cachep;
    +
    + if (s)
    + pages += kmem_estimate_pages(s, flags, 0);
    + }
    +
    + return pages;
    +}
    +EXPORT_SYMBOL_GPL(kestimate);
    +
    +/*
    * This initializes kmem_list3 or resizes various caches for all nodes.
    */
    static int alloc_kmemlist(struct kmem_cache *cachep)
    --



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