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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>
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1 parent e968756 commit ca279cf1065fb689abea1dc7d8c11787729bb185 @Benjamin-Gaignard Benjamin-Gaignard committed with Oct 5, 2012
Showing with 111 additions and 4 deletions.
  1. +27 −0 include/linux/genalloc.h
  2. +84 −4 lib/genalloc.c
View
27 include/linux/genalloc.h
@@ -29,13 +29,30 @@
#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.
*/
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__ */
View
88 lib/genalloc.c
@@ -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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