Commit ca279cf1 authored by Benjamin Gaignard's avatar Benjamin Gaignard Committed by Linus Torvalds
Browse files

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: default avatarBenjamin Gaignard <benjamin.gaignard@stericsson.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e9687567

include/linux/genalloc.h

+27 −0
Original line number Diff line number Diff line
@@ -29,6 +29,20 @@ 


#ifndef __GENALLOC_H__

#define __GENALLOC_H__

/**

 * Allocation callback function type definition

 * @map: Pointer to bitmap

 * @size: The bitmap size in bits

 * @start: The bitnumber to start searching at

 * @nr: The number of zeroed bits we're looking for

 * @data: optional additional data used by @genpool_algo_t

 */

typedef unsigned long (*genpool_algo_t)(unsigned long *map,

			unsigned long size,

			unsigned long start,

			unsigned int nr,

			void *data);



/*

 *  General purpose special memory pool descriptor.

 */
@@ -36,6 +50,9 @@ struct gen_pool { 
	spinlock_t lock;

	struct list_head chunks;	/* list of chunks in this pool */

	int min_alloc_order;		/* minimum allocation order */



	genpool_algo_t algo;		/* allocation function */

	void *data;

};



/*
@@ -78,4 +95,14 @@ extern void gen_pool_for_each_chunk(struct gen_pool *, 
	void (*)(struct gen_pool *, struct gen_pool_chunk *, void *), void *);

extern size_t gen_pool_avail(struct gen_pool *);

extern size_t gen_pool_size(struct gen_pool *);



extern void gen_pool_set_algo(struct gen_pool *pool, genpool_algo_t algo,

		void *data);



extern unsigned long gen_pool_first_fit(unsigned long *map, unsigned long size,

		unsigned long start, unsigned int nr, void *data);



extern unsigned long gen_pool_best_fit(unsigned long *map, unsigned long size,

		unsigned long start, unsigned int nr, void *data);



#endif /* __GENALLOC_H__ */

lib/genalloc.c

+84 −4
Original line number Diff line number Diff line
@@ -152,6 +152,8 @@ struct gen_pool *gen_pool_create(int min_alloc_order, int nid) 
		spin_lock_init(&pool->lock);

		INIT_LIST_HEAD(&pool->chunks);

		pool->min_alloc_order = min_alloc_order;

		pool->algo = gen_pool_first_fit;

		pool->data = NULL;

	}

	return pool;

}
@@ -255,8 +257,9 @@ EXPORT_SYMBOL(gen_pool_destroy); 
 * @size: number of bytes to allocate from the pool

 *

 * Allocate the requested number of bytes from the specified pool.

 * Uses a first-fit algorithm. Can not be used in NMI handler on

 * architectures without NMI-safe cmpxchg implementation.

 * Uses the pool allocation function (with first-fit algorithm by default).

 * Can not be used in NMI handler on architectures without

 * NMI-safe cmpxchg implementation.

 */

unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size)

{
@@ -280,8 +283,8 @@ unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size) 


		end_bit = (chunk->end_addr - chunk->start_addr) >> order;

retry:

		start_bit = bitmap_find_next_zero_area(chunk->bits, end_bit,

						       start_bit, nbits, 0);

		start_bit = pool->algo(chunk->bits, end_bit, start_bit, nbits,

				pool->data);

		if (start_bit >= end_bit)

			continue;

		remain = bitmap_set_ll(chunk->bits, start_bit, nbits);
@@ -400,3 +403,80 @@ size_t gen_pool_size(struct gen_pool *pool) 
	return size;

}

EXPORT_SYMBOL_GPL(gen_pool_size);



/**

 * gen_pool_set_algo - set the allocation algorithm

 * @pool: pool to change allocation algorithm

 * @algo: custom algorithm function

 * @data: additional data used by @algo

 *

 * Call @algo for each memory allocation in the pool.

 * If @algo is NULL use gen_pool_first_fit as default

 * memory allocation function.

 */

void gen_pool_set_algo(struct gen_pool *pool, genpool_algo_t algo, void *data)

{

	rcu_read_lock();



	pool->algo = algo;

	if (!pool->algo)

		pool->algo = gen_pool_first_fit;



	pool->data = data;



	rcu_read_unlock();

}

EXPORT_SYMBOL(gen_pool_set_algo);



/**

 * gen_pool_first_fit - find the first available region

 * of memory matching the size requirement (no alignment constraint)

 * @map: The address to base the search on

 * @size: The bitmap size in bits

 * @start: The bitnumber to start searching at

 * @nr: The number of zeroed bits we're looking for

 * @data: additional data - unused

 */

unsigned long gen_pool_first_fit(unsigned long *map, unsigned long size,

		unsigned long start, unsigned int nr, void *data)

{

	return bitmap_find_next_zero_area(map, size, start, nr, 0);

}

EXPORT_SYMBOL(gen_pool_first_fit);



/**

 * gen_pool_best_fit - find the best fitting region of memory

 * macthing the size requirement (no alignment constraint)

 * @map: The address to base the search on

 * @size: The bitmap size in bits

 * @start: The bitnumber to start searching at

 * @nr: The number of zeroed bits we're looking for

 * @data: additional data - unused

 *

 * Iterate over the bitmap to find the smallest free region

 * which we can allocate the memory.

 */

unsigned long gen_pool_best_fit(unsigned long *map, unsigned long size,

		unsigned long start, unsigned int nr, void *data)

{

	unsigned long start_bit = size;

	unsigned long len = size + 1;

	unsigned long index;



	index = bitmap_find_next_zero_area(map, size, start, nr, 0);



	while (index < size) {

		int next_bit = find_next_bit(map, size, index + nr);

		if ((next_bit - index) < len) {

			len = next_bit - index;

			start_bit = index;

			if (len == nr)

				return start_bit;

		}

		index = bitmap_find_next_zero_area(map, size,

						   next_bit + 1, nr, 0);

	}



	return start_bit;

}

EXPORT_SYMBOL(gen_pool_best_fit);

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