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pool: Improve memory usage for devices which can't cross boundaries

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The previous implementation simply refused to allocate more than a
boundary's worth of data from an entire page.  Some users didn't know
this, so specified things like SMP_CACHE_BYTES, not realising the
horrible waste of memory that this was.  It's fairly easy to correct
this problem, just by ensuring we don't cross a boundary within a page.
This even helps drivers like EHCI (which can't cross a 4k boundary)
on machines with larger page sizes.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Matthew Wilcox 2007-12-03 14:16:24 -05:00
parent a35a345514
commit e34f44b351
1 changed files with 21 additions and 17 deletions
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38
mm/dmapool.c
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@ -43,6 +43,7 @@ struct dma_pool { /* the pool */
size_t size; size_t size;
struct device *dev; struct device *dev;
size_t allocation; size_t allocation;
size_t boundary;
char name[32]; char name[32];
wait_queue_head_t waitq; wait_queue_head_t waitq;
struct list_head pools; struct list_head pools;
@ -107,7 +108,7 @@ static DEVICE_ATTR(pools, S_IRUGO, show_pools, NULL);
* @dev: device that will be doing the DMA * @dev: device that will be doing the DMA
* @size: size of the blocks in this pool. * @size: size of the blocks in this pool.
* @align: alignment requirement for blocks; must be a power of two * @align: alignment requirement for blocks; must be a power of two
* @allocation: returned blocks won't cross this boundary (or zero) * @boundary: returned blocks won't cross this power of two boundary
* Context: !in_interrupt() * Context: !in_interrupt()
* *
* Returns a dma allocation pool with the requested characteristics, or * Returns a dma allocation pool with the requested characteristics, or
@ -117,15 +118,16 @@ static DEVICE_ATTR(pools, S_IRUGO, show_pools, NULL);
* cache flushing primitives. The actual size of blocks allocated may be * cache flushing primitives. The actual size of blocks allocated may be
* larger than requested because of alignment. * larger than requested because of alignment.
* *
* If allocation is nonzero, objects returned from dma_pool_alloc() won't * If @boundary is nonzero, objects returned from dma_pool_alloc() won't
* cross that size boundary. This is useful for devices which have * cross that size boundary. This is useful for devices which have
* addressing restrictions on individual DMA transfers, such as not crossing * addressing restrictions on individual DMA transfers, such as not crossing
* boundaries of 4KBytes. * boundaries of 4KBytes.
*/ */
struct dma_pool *dma_pool_create(const char *name, struct device *dev, struct dma_pool *dma_pool_create(const char *name, struct device *dev,
size_t size, size_t align, size_t allocation) size_t size, size_t align, size_t boundary)
{ {
struct dma_pool *retval; struct dma_pool *retval;
size_t allocation;
if (align == 0) { if (align == 0) {
align = 1; align = 1;
@ -142,27 +144,26 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
if ((size % align) != 0) if ((size % align) != 0)
size = ALIGN(size, align); size = ALIGN(size, align);
if (allocation == 0) { allocation = max_t(size_t, size, PAGE_SIZE);
if (PAGE_SIZE < size)
allocation = size;
else
allocation = PAGE_SIZE;
/* FIXME: round up for less fragmentation */
} else if (allocation < size)
return NULL;
if (! if (!boundary) {
(retval = boundary = allocation;
kmalloc_node(sizeof *retval, GFP_KERNEL, dev_to_node(dev)))) } else if ((boundary < size) || (boundary & (boundary - 1))) {
return NULL;
}
retval = kmalloc_node(sizeof(*retval), GFP_KERNEL, dev_to_node(dev));
if (!retval)
return retval; return retval;
strlcpy(retval->name, name, sizeof retval->name); strlcpy(retval->name, name, sizeof(retval->name));
retval->dev = dev; retval->dev = dev;
INIT_LIST_HEAD(&retval->page_list); INIT_LIST_HEAD(&retval->page_list);
spin_lock_init(&retval->lock); spin_lock_init(&retval->lock);
retval->size = size; retval->size = size;
retval->boundary = boundary;
retval->allocation = allocation; retval->allocation = allocation;
init_waitqueue_head(&retval->waitq); init_waitqueue_head(&retval->waitq);
@ -192,11 +193,14 @@ EXPORT_SYMBOL(dma_pool_create);
static void pool_initialise_page(struct dma_pool *pool, struct dma_page *page) static void pool_initialise_page(struct dma_pool *pool, struct dma_page *page)
{ {
unsigned int offset = 0; unsigned int offset = 0;
unsigned int next_boundary = pool->boundary;
do { do {
unsigned int next = offset + pool->size; unsigned int next = offset + pool->size;
if (unlikely((next + pool->size) >= pool->allocation)) if (unlikely((next + pool->size) >= next_boundary)) {
next = pool->allocation; next = next_boundary;
next_boundary += pool->boundary;
}
*(int *)(page->vaddr + offset) = next; *(int *)(page->vaddr + offset) = next;
offset = next; offset = next;
} while (offset < pool->allocation); } while (offset < pool->allocation);