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: Matthew Wilcox <willy@linux.intel.com>
Acked-by: David S. Miller <davem@davemloft.net>

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 72e7ece..34aaac4 100644 (file)
--- 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);