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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>
109 lines
4.0 KiB
C
109 lines
4.0 KiB
C
/*
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* Basic general purpose allocator for managing special purpose
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* memory, for example, memory that is not managed by the regular
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* kmalloc/kfree interface. Uses for this includes on-device special
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* memory, uncached memory etc.
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*
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* It is safe to use the allocator in NMI handlers and other special
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* unblockable contexts that could otherwise deadlock on locks. This
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* is implemented by using atomic operations and retries on any
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* conflicts. The disadvantage is that there may be livelocks in
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* extreme cases. For better scalability, one allocator can be used
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* for each CPU.
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*
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* The lockless operation only works if there is enough memory
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* available. If new memory is added to the pool a lock has to be
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* still taken. So any user relying on locklessness has to ensure
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* that sufficient memory is preallocated.
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*
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* The basic atomic operation of this allocator is cmpxchg on long.
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* On architectures that don't have NMI-safe cmpxchg implementation,
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* the allocator can NOT be used in NMI handler. So code uses the
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* allocator in NMI handler should depend on
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* CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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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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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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* General purpose special memory pool chunk descriptor.
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*/
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struct gen_pool_chunk {
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struct list_head next_chunk; /* next chunk in pool */
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atomic_t avail;
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phys_addr_t phys_addr; /* physical starting address of memory chunk */
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unsigned long start_addr; /* starting address of memory chunk */
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unsigned long end_addr; /* ending address of memory chunk */
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unsigned long bits[0]; /* bitmap for allocating memory chunk */
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};
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extern struct gen_pool *gen_pool_create(int, int);
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extern phys_addr_t gen_pool_virt_to_phys(struct gen_pool *pool, unsigned long);
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extern int gen_pool_add_virt(struct gen_pool *, unsigned long, phys_addr_t,
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size_t, int);
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/**
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* gen_pool_add - add a new chunk of special memory to the pool
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* @pool: pool to add new memory chunk to
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* @addr: starting address of memory chunk to add to pool
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* @size: size in bytes of the memory chunk to add to pool
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* @nid: node id of the node the chunk structure and bitmap should be
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* allocated on, or -1
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*
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* Add a new chunk of special memory to the specified pool.
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*
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* Returns 0 on success or a -ve errno on failure.
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*/
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static inline int gen_pool_add(struct gen_pool *pool, unsigned long addr,
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size_t size, int nid)
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{
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return gen_pool_add_virt(pool, addr, -1, size, nid);
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}
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extern void gen_pool_destroy(struct gen_pool *);
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extern unsigned long gen_pool_alloc(struct gen_pool *, size_t);
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extern void gen_pool_free(struct gen_pool *, unsigned long, size_t);
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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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