Provide a method to get the upper bound on the pages needed to allocate
a given number of objects from a given kmem_cache.

Signed-off-by: Peter Zijlstra
---
include/linux/slab.h | 3 +
mm/slub.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++ +
2 files changed, 85 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
@@ -2293,6 +2293,37 @@ 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.
*/
@@ -2630,6 +2661,57 @@ void kfree(const void *x)
EXPORT_SYMBOL(kfree);

/*
+ * 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

--

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