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slob: improved alignment handling

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Remove the core slob allocator's minimum alignment restrictions, and instead
introduce the alignment restrictions at the slab API layer.  This lets us heed
the ARCH_KMALLOC/SLAB_MINALIGN directives, and also use __alignof__ (unsigned
long) for the default alignment (which should allow relaxed alignment
architectures to take better advantage of SLOB's small minimum alignment).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2007-07-15 23:38:09 -07:00 committed by Linus Torvalds
parent d87a133fc2
commit 553948491c
1 changed files with 26 additions and 23 deletions
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49
mm/slob.c
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@ -7,8 +7,8 @@
*
* The core of SLOB is a traditional K&R style heap allocator, with
* support for returning aligned objects. The granularity of this
* allocator is 4 bytes on 32-bit and 8 bytes on 64-bit, though it
* could be as low as 2 if the compiler alignment requirements allow.
* allocator is as little as 2 bytes, however typically most architectures
* will require 4 bytes on 32-bit and 8 bytes on 64-bit.
*
* The slob heap is a linked list of pages from __get_free_page, and
* within each page, there is a singly-linked list of free blocks (slob_t).
@ -16,7 +16,7 @@
* first-fit.
*
* Above this is an implementation of kmalloc/kfree. Blocks returned
* from kmalloc are 4-byte aligned and prepended with a 4-byte header.
* from kmalloc are prepended with a 4-byte header with the kmalloc size.
* If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
* __get_free_pages directly, allocating compound pages so the page order
* does not have to be separately tracked, and also stores the exact
@ -45,13 +45,6 @@
#include <linux/list.h>
#include <asm/atomic.h>
/* SLOB_MIN_ALIGN == sizeof(long) */
#if BITS_PER_BYTE == 32
#define SLOB_MIN_ALIGN 4
#else
#define SLOB_MIN_ALIGN 8
#endif
/*
* slob_block has a field 'units', which indicates size of block if +ve,
* or offset of next block if -ve (in SLOB_UNITs).
@ -60,19 +53,15 @@
* Those with larger size contain their size in the first SLOB_UNIT of
* memory, and the offset of the next free block in the second SLOB_UNIT.
*/
#if PAGE_SIZE <= (32767 * SLOB_MIN_ALIGN)
#if PAGE_SIZE <= (32767 * 2)
typedef s16 slobidx_t;
#else
typedef s32 slobidx_t;
#endif
/*
* Align struct slob_block to long for now, but can some embedded
* architectures get away with less?
*/
struct slob_block {
slobidx_t units;
} __attribute__((aligned(SLOB_MIN_ALIGN)));
};
typedef struct slob_block slob_t;
/*
@ -384,14 +373,25 @@ static void slob_free(void *block, int size)
* End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
*/
#ifndef ARCH_KMALLOC_MINALIGN
#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)
#endif
#ifndef ARCH_SLAB_MINALIGN
#define ARCH_SLAB_MINALIGN __alignof__(unsigned long)
#endif
void *__kmalloc(size_t size, gfp_t gfp)
{
if (size < PAGE_SIZE - SLOB_UNIT) {
slob_t *m;
m = slob_alloc(size + SLOB_UNIT, gfp, 0);
int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
if (size < PAGE_SIZE - align) {
unsigned int *m;
m = slob_alloc(size + align, gfp, align);
if (m)
m->units = size;
return m+1;
*m = size;
return (void *)m + align;
} else {
void *ret;
@ -449,8 +449,9 @@ void kfree(const void *block)
sp = (struct slob_page *)virt_to_page(block);
if (slob_page(sp)) {
slob_t *m = (slob_t *)block - 1;
slob_free(m, m->units + SLOB_UNIT);
int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
unsigned int *m = (unsigned int *)(block - align);
slob_free(m, *m + align);
} else
put_page(&sp->page);
}
@ -499,6 +500,8 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
c->ctor = ctor;
/* ignore alignment unless it's forced */
c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
if (c->align < ARCH_SLAB_MINALIGN)
c->align = ARCH_SLAB_MINALIGN;
if (c->align < align)
c->align = align;
} else if (flags & SLAB_PANIC)