genalloc: make it possible to use a custom allocation algorithm
Premit use of another algorithm than the default first-fit one. For
example a custom algorithm could be used to manage alignment requirements.
As I can't predict all the possible requirements/needs for all allocation
uses cases, I add a "free" field 'void *data' to pass any needed
information to the allocation function. For example 'data' could be used
to handle a structure where you store the alignment, the expected memory
bank, the requester device, or any information that could influence the
allocation algorithm.
An usage example may look like this:
struct my_pool_constraints {
int align;
int bank;
...
};
unsigned long my_custom_algo(unsigned long *map, unsigned long size,
unsigned long start, unsigned int nr, void *data)
{
struct my_pool_constraints *constraints = data;
...
deal with allocation contraints
...
return the index in bitmap where perform the allocation
}
void create_my_pool()
{
struct my_pool_constraints c;
struct gen_pool *pool = gen_pool_create(...);
gen_pool_add(pool, ...);
gen_pool_set_algo(pool, my_custom_algo, &c);
}
Add of best-fit algorithm function:
most of the time best-fit is slower then first-fit but memory fragmentation
is lower. The random buffer allocation/free tests don't show any arithmetic
relation between the allocation time and fragmentation but the
best-fit algorithm
is sometime able to perform the allocation when the first-fit can't.
This new algorithm help to remove static allocations on ESRAM, a small but
fast on-chip RAM of few KB, used for high-performance uses cases like DMA
linked lists, graphic accelerators, encoders/decoders. On the Ux500
(in the ARM tree) we have define 5 ESRAM banks of 128 KB each and use of
static allocations becomes unmaintainable:
cd arch/arm/mach-ux500 && grep -r ESRAM .
./include/mach/db8500-regs.h:/* Base address and bank offsets for ESRAM */
./include/mach/db8500-regs.h:#define U8500_ESRAM_BASE 0x40000000
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK_SIZE 0x00020000
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK0 U8500_ESRAM_BASE
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK1 (U8500_ESRAM_BASE + U8500_ESRAM_BANK_SIZE)
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK2 (U8500_ESRAM_BANK1 + U8500_ESRAM_BANK_SIZE)
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK3 (U8500_ESRAM_BANK2 + U8500_ESRAM_BANK_SIZE)
./include/mach/db8500-regs.h:#define U8500_ESRAM_BANK4 (U8500_ESRAM_BANK3 + U8500_ESRAM_BANK_SIZE)
./include/mach/db8500-regs.h:#define U8500_ESRAM_DMA_LCPA_OFFSET 0x10000
./include/mach/db8500-regs.h:#define U8500_DMA_LCPA_BASE
(U8500_ESRAM_BANK0 + U8500_ESRAM_DMA_LCPA_OFFSET)
./include/mach/db8500-regs.h:#define U8500_DMA_LCLA_BASE U8500_ESRAM_BANK4
I want to use genalloc to do dynamic allocations but I need to be able to
fine tune the allocation algorithm. I my case best-fit algorithm give
better results than first-fit, but it will not be true for every use case.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@stericsson.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Benjamin Gaignard
Linus Torvalds
parent
e96875677f
commit
ca279cf106
2 changed files with 111 additions and 4 deletions
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@ -29,6 +29,20 @@
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#ifndef __GENALLOC_H__
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#define __GENALLOC_H__
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/**
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* Allocation callback function type definition
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* @map: Pointer to bitmap
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* @size: The bitmap size in bits
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* @start: The bitnumber to start searching at
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* @nr: The number of zeroed bits we're looking for
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* @data: optional additional data used by @genpool_algo_t
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*/
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typedef unsigned long (*genpool_algo_t)(unsigned long *map,
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unsigned long size,
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unsigned long start,
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unsigned int nr,
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void *data);
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/*
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* General purpose special memory pool descriptor.
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*/
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@ -36,6 +50,9 @@ struct gen_pool {
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spinlock_t lock;
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struct list_head chunks; /* list of chunks in this pool */
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int min_alloc_order; /* minimum allocation order */
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genpool_algo_t algo; /* allocation function */
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void *data;
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};
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/*
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@ -78,4 +95,14 @@ extern void gen_pool_for_each_chunk(struct gen_pool *,
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void (*)(struct gen_pool *, struct gen_pool_chunk *, void *), void *);
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extern size_t gen_pool_avail(struct gen_pool *);
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extern size_t gen_pool_size(struct gen_pool *);
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extern void gen_pool_set_algo(struct gen_pool *pool, genpool_algo_t algo,
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void *data);
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extern unsigned long gen_pool_first_fit(unsigned long *map, unsigned long size,
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unsigned long start, unsigned int nr, void *data);
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extern unsigned long gen_pool_best_fit(unsigned long *map, unsigned long size,
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unsigned long start, unsigned int nr, void *data);
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#endif /* __GENALLOC_H__ */
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@ -152,6 +152,8 @@ struct gen_pool *gen_pool_create(int min_alloc_order, int nid)
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spin_lock_init(&pool->lock);
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INIT_LIST_HEAD(&pool->chunks);
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pool->min_alloc_order = min_alloc_order;
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pool->algo = gen_pool_first_fit;
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pool->data = NULL;
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}
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return pool;
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}
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@ -255,8 +257,9 @@ EXPORT_SYMBOL(gen_pool_destroy);
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* @size: number of bytes to allocate from the pool
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*
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* Allocate the requested number of bytes from the specified pool.
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* Uses a first-fit algorithm. Can not be used in NMI handler on
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* architectures without NMI-safe cmpxchg implementation.
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* Uses the pool allocation function (with first-fit algorithm by default).
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* Can not be used in NMI handler on architectures without
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* NMI-safe cmpxchg implementation.
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*/
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unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size)
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{
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@ -280,8 +283,8 @@ unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size)
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end_bit = (chunk->end_addr - chunk->start_addr) >> order;
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retry:
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start_bit = bitmap_find_next_zero_area(chunk->bits, end_bit,
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start_bit, nbits, 0);
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start_bit = pool->algo(chunk->bits, end_bit, start_bit, nbits,
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pool->data);
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if (start_bit >= end_bit)
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continue;
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remain = bitmap_set_ll(chunk->bits, start_bit, nbits);
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@ -400,3 +403,80 @@ size_t gen_pool_size(struct gen_pool *pool)
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return size;
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}
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EXPORT_SYMBOL_GPL(gen_pool_size);
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/**
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* gen_pool_set_algo - set the allocation algorithm
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* @pool: pool to change allocation algorithm
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* @algo: custom algorithm function
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* @data: additional data used by @algo
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*
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* Call @algo for each memory allocation in the pool.
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* If @algo is NULL use gen_pool_first_fit as default
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* memory allocation function.
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*/
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void gen_pool_set_algo(struct gen_pool *pool, genpool_algo_t algo, void *data)
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{
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rcu_read_lock();
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pool->algo = algo;
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if (!pool->algo)
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pool->algo = gen_pool_first_fit;
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pool->data = data;
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rcu_read_unlock();
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}
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EXPORT_SYMBOL(gen_pool_set_algo);
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/**
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* gen_pool_first_fit - find the first available region
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* of memory matching the size requirement (no alignment constraint)
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* @map: The address to base the search on
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* @size: The bitmap size in bits
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* @start: The bitnumber to start searching at
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* @nr: The number of zeroed bits we're looking for
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* @data: additional data - unused
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*/
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unsigned long gen_pool_first_fit(unsigned long *map, unsigned long size,
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unsigned long start, unsigned int nr, void *data)
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{
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return bitmap_find_next_zero_area(map, size, start, nr, 0);
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}
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EXPORT_SYMBOL(gen_pool_first_fit);
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/**
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* gen_pool_best_fit - find the best fitting region of memory
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* macthing the size requirement (no alignment constraint)
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* @map: The address to base the search on
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* @size: The bitmap size in bits
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* @start: The bitnumber to start searching at
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* @nr: The number of zeroed bits we're looking for
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* @data: additional data - unused
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*
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* Iterate over the bitmap to find the smallest free region
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* which we can allocate the memory.
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*/
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unsigned long gen_pool_best_fit(unsigned long *map, unsigned long size,
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unsigned long start, unsigned int nr, void *data)
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{
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unsigned long start_bit = size;
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unsigned long len = size + 1;
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unsigned long index;
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index = bitmap_find_next_zero_area(map, size, start, nr, 0);
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while (index < size) {
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int next_bit = find_next_bit(map, size, index + nr);
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if ((next_bit - index) < len) {
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len = next_bit - index;
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start_bit = index;
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if (len == nr)
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return start_bit;
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}
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index = bitmap_find_next_zero_area(map, size,
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next_bit + 1, nr, 0);
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}
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return start_bit;
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}
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EXPORT_SYMBOL(gen_pool_best_fit);
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