slab: Common Kmalloc cache determination
Extract the optimized lookup functions from slub and put them into slab_common.c. Then make slab use these functions as well. Joonsoo notes that this fixes some issues with constant folding which also reduces the code size for slub. https://lkml.org/lkml/2012/10/20/82 Signed-off-by: Christoph Lameter <cl@linux.com> Signed-off-by: Pekka Enberg <penberg@kernel.org>
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Pekka Enberg

parent
9e5e8deca7
commit
2c59dd6544
105
mm/slab_common.c
105
mm/slab_common.c
@@ -327,6 +327,68 @@ struct kmem_cache *kmalloc_dma_caches[KMALLOC_SHIFT_HIGH + 1];
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EXPORT_SYMBOL(kmalloc_dma_caches);
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#endif
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/*
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* Conversion table for small slabs sizes / 8 to the index in the
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* kmalloc array. This is necessary for slabs < 192 since we have non power
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* of two cache sizes there. The size of larger slabs can be determined using
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* fls.
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*/
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static s8 size_index[24] = {
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3, /* 8 */
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4, /* 16 */
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5, /* 24 */
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5, /* 32 */
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6, /* 40 */
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6, /* 48 */
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6, /* 56 */
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6, /* 64 */
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1, /* 72 */
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1, /* 80 */
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1, /* 88 */
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1, /* 96 */
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7, /* 104 */
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7, /* 112 */
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7, /* 120 */
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7, /* 128 */
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2, /* 136 */
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2, /* 144 */
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2, /* 152 */
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2, /* 160 */
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2, /* 168 */
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2, /* 176 */
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2, /* 184 */
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2 /* 192 */
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};
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static inline int size_index_elem(size_t bytes)
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{
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return (bytes - 1) / 8;
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}
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/*
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* Find the kmem_cache structure that serves a given size of
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* allocation
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*/
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struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
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{
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int index;
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if (size <= 192) {
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if (!size)
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return ZERO_SIZE_PTR;
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index = size_index[size_index_elem(size)];
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} else
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index = fls(size - 1);
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#ifdef CONFIG_ZONE_DMA
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if (unlikely((flags & SLAB_CACHE_DMA)))
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return kmalloc_dma_caches[index];
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#endif
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return kmalloc_caches[index];
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}
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/*
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* Create the kmalloc array. Some of the regular kmalloc arrays
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* may already have been created because they were needed to
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@@ -336,6 +398,47 @@ void __init create_kmalloc_caches(unsigned long flags)
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{
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int i;
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/*
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* Patch up the size_index table if we have strange large alignment
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* requirements for the kmalloc array. This is only the case for
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* MIPS it seems. The standard arches will not generate any code here.
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*
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* Largest permitted alignment is 256 bytes due to the way we
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* handle the index determination for the smaller caches.
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*
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* Make sure that nothing crazy happens if someone starts tinkering
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* around with ARCH_KMALLOC_MINALIGN
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*/
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BUILD_BUG_ON(KMALLOC_MIN_SIZE > 256 ||
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(KMALLOC_MIN_SIZE & (KMALLOC_MIN_SIZE - 1)));
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for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
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int elem = size_index_elem(i);
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if (elem >= ARRAY_SIZE(size_index))
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break;
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size_index[elem] = KMALLOC_SHIFT_LOW;
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}
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if (KMALLOC_MIN_SIZE >= 64) {
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/*
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* The 96 byte size cache is not used if the alignment
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* is 64 byte.
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*/
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for (i = 64 + 8; i <= 96; i += 8)
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size_index[size_index_elem(i)] = 7;
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}
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if (KMALLOC_MIN_SIZE >= 128) {
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/*
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* The 192 byte sized cache is not used if the alignment
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* is 128 byte. Redirect kmalloc to use the 256 byte cache
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* instead.
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*/
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for (i = 128 + 8; i <= 192; i += 8)
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size_index[size_index_elem(i)] = 8;
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}
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/* Caches that are not of the two-to-the-power-of size */
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if (KMALLOC_MIN_SIZE <= 32 && !kmalloc_caches[1])
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kmalloc_caches[1] = create_kmalloc_cache(NULL, 96, flags);
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@@ -379,8 +482,6 @@ void __init create_kmalloc_caches(unsigned long flags)
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}
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#endif
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}
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#endif /* !CONFIG_SLOB */
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