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Subject[PATCH 7/7] pool: Improve memory usage for devices which can't cross boundaries
Date
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>
---
mm/dmapool.c | 36 ++++++++++++++++++++----------------
1 files changed, 20 insertions(+), 16 deletions(-)
diff --git a/mm/dmapool.c b/mm/dmapool.c
index 72e7ece..34aaac4 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -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;
- else
- 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;

INIT_LIST_HEAD(&retval->page_list);
spin_lock_init(&retval->lock);
retval->size = size;
+ retval->boundary = boundary;
retval->allocation = allocation;
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)
{
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);
--
1.4.4.4

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