Commit e34f44b3 authored by Matthew Wilcox's avatar Matthew Wilcox
Browse files

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

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: default avatarMatthew Wilcox <>
Acked-by: default avatarDavid S. Miller <>
parent a35a3455
......@@ -43,6 +43,7 @@ struct dma_pool { /* the pool */
size_t size;
struct device *dev;
size_t allocation;
size_t boundary;
char name[32];
wait_queue_head_t waitq;
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
* @size: size of the blocks in this pool.
* @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()
* 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
* 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
* addressing restrictions on individual DMA transfers, such as not crossing
* boundaries of 4KBytes.
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;
size_t allocation;
if (align == 0) {
align = 1;
......@@ -142,27 +144,26 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
if ((size % align) != 0)
size = ALIGN(size, align);
if (allocation == 0) {
if (PAGE_SIZE < size)
allocation = size;
allocation = PAGE_SIZE;
/* FIXME: round up for less fragmentation */
} else if (allocation < size)
allocation = max_t(size_t, size, PAGE_SIZE);
if (!boundary) {
boundary = allocation;
} else if ((boundary < size) || (boundary & (boundary - 1))) {
return NULL;
if (!
(retval =
kmalloc_node(sizeof *retval, GFP_KERNEL, dev_to_node(dev))))
retval = kmalloc_node(sizeof(*retval), GFP_KERNEL, dev_to_node(dev));
if (!retval)
return retval;
strlcpy(retval->name, name, sizeof retval->name);
strlcpy(retval->name, name, sizeof(retval->name));
retval->dev = dev;
retval->size = size;
retval->boundary = boundary;
retval->allocation = allocation;
......@@ -192,11 +193,14 @@ EXPORT_SYMBOL(dma_pool_create);
static void pool_initialise_page(struct dma_pool *pool, struct dma_page *page)
unsigned int offset = 0;
unsigned int next_boundary = pool->boundary;
do {
unsigned int next = offset + pool->size;
if (unlikely((next + pool->size) >= pool->allocation))
next = pool->allocation;
if (unlikely((next + pool->size) >= next_boundary)) {
next = next_boundary;
next_boundary += pool->boundary;
*(int *)(page->vaddr + offset) = next;
offset = next;
} while (offset < pool->allocation);
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