Change dmapool free block management

Use a list of free blocks within a page instead of using a bitmap.
Update documentation to reflect this.  As well as being a slight
reduction in memory allocation, locked ops and lines of code, it speeds
up a transaction processing benchmark by 0.4%.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

1 files changed, 58 insertions, 61 deletions

diff --git a/mm/dmapool.c b/mm/dmapool.c
index e2ea4543abb4..72e7ece7ee9d 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -17,7 +17,9 @@
  * The current design of this allocator is fairly simple.  The pool is
  * represented by the 'struct dma_pool' which keeps a doubly-linked list of
  * allocated pages.  Each page in the page_list is split into blocks of at
- * least 'size' bytes.
+ * least 'size' bytes.  Free blocks are tracked in an unsorted singly-linked
+ * list of free blocks within the page.  Used blocks aren't tracked, but we
+ * keep a count of how many are currently allocated from each page.
  */
 
 #include <linux/device.h>
@@ -38,7 +40,6 @@
 struct dma_pool {               /* the pool */
         struct list_head page_list;
         spinlock_t lock;
-        size_t blocks_per_page;
         size_t size;
         struct device *dev;
         size_t allocation;
@@ -51,8 +52,8 @@ struct dma_page {		/* cacheable header for 'allocation' bytes */
         struct list_head page_list;
         void *vaddr;
         dma_addr_t dma;
-        unsigned in_use;
-        unsigned long bitmap[0];
+        unsigned int in_use;
+        unsigned int offset;
 };
 
 #define POOL_TIMEOUT_JIFFIES    ((100 /* msec */ * HZ) / 1000)
@@ -87,8 +88,8 @@ show_pools(struct device *dev, struct device_attribute *attr, char *buf)
 
                 /* per-pool info, no real statistics yet */
                 temp = scnprintf(next, size, "%-16s %4u %4Zu %4Zu %2u\n",
-                                 pool->name,
-                                 blocks, pages * pool->blocks_per_page,
+                                 pool->name, blocks,
+                                 pages * (pool->allocation / pool->size),
                                  pool->size, pages);
                 size -= temp;
                 next += temp;
@@ -132,8 +133,11 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
                 return NULL;
         }
 
-        if (size == 0)
+        if (size == 0) {
                 return NULL;
+        } else if (size < 4) {
+                size = 4;
+        }
 
         if ((size % align) != 0)
                 size = ALIGN(size, align);
@@ -160,7 +164,6 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
         spin_lock_init(&retval->lock);
         retval->size = size;
         retval->allocation = allocation;
-        retval->blocks_per_page = allocation / size;
         init_waitqueue_head(&retval->waitq);
 
         if (dev) {
@@ -186,28 +189,36 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 }
 EXPORT_SYMBOL(dma_pool_create);
 
+static void pool_initialise_page(struct dma_pool *pool, struct dma_page *page)
+{
+        unsigned int offset = 0;
+
+        do {
+                unsigned int next = offset + pool->size;
+                if (unlikely((next + pool->size) >= pool->allocation))
+                        next = pool->allocation;
+                *(int *)(page->vaddr + offset) = next;
+                offset = next;
+        } while (offset < pool->allocation);
+}
+
 static struct dma_page *pool_alloc_page(struct dma_pool *pool, gfp_t mem_flags)
 {
         struct dma_page *page;
-        int mapsize;
-
-        mapsize = pool->blocks_per_page;
-        mapsize = (mapsize + BITS_PER_LONG - 1) / BITS_PER_LONG;
-        mapsize *= sizeof(long);
 
-        page = kmalloc(mapsize + sizeof *page, mem_flags);
+        page = kmalloc(sizeof(*page), mem_flags);
         if (!page)
                 return NULL;
-        page->vaddr = dma_alloc_coherent(pool->dev,
-                                         pool->allocation,
+        page->vaddr = dma_alloc_coherent(pool->dev, pool->allocation,
                                          &page->dma, mem_flags);
         if (page->vaddr) {
-                memset(page->bitmap, 0xff, mapsize);    /* bit set == free */
 #ifdef  CONFIG_DEBUG_SLAB
                 memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
 #endif
+                pool_initialise_page(pool, page);
                 list_add(&page->page_list, &pool->page_list);
                 page->in_use = 0;
+                page->offset = 0;
         } else {
                 kfree(page);
                 page = NULL;
@@ -215,14 +226,9 @@ static struct dma_page *pool_alloc_page(struct dma_pool *pool, gfp_t mem_flags)
         return page;
 }
 
-static inline int is_page_busy(int blocks, unsigned long *bitmap)
+static inline int is_page_busy(struct dma_page *page)
 {
-        while (blocks > 0) {
-                if (*bitmap++ != ~0UL)
-                        return 1;
-                blocks -= BITS_PER_LONG;
-        }
-        return 0;
+        return page->in_use != 0;
 }
 
 static void pool_free_page(struct dma_pool *pool, struct dma_page *page)
@@ -257,7 +263,7 @@ void dma_pool_destroy(struct dma_pool *pool)
                 struct dma_page *page;
                 page = list_entry(pool->page_list.next,
                                   struct dma_page, page_list);
-                if (is_page_busy(pool->blocks_per_page, page->bitmap)) {
+                if (is_page_busy(page)) {
                         if (pool->dev)
                                 dev_err(pool->dev,
                                         "dma_pool_destroy %s, %p busy\n",
@@ -292,27 +298,14 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
 {
         unsigned long flags;
         struct dma_page *page;
-        int map, block;
         size_t offset;
         void *retval;
 
         spin_lock_irqsave(&pool->lock, flags);
  restart:
         list_for_each_entry(page, &pool->page_list, page_list) {
-                int i;
-                /* only cachable accesses here ... */
-                for (map = 0, i = 0;
-                     i < pool->blocks_per_page; i += BITS_PER_LONG, map++) {
-                        if (page->bitmap[map] == 0)
-                                continue;
-                        block = ffz(~page->bitmap[map]);
-                        if ((i + block) < pool->blocks_per_page) {
-                                clear_bit(block, &page->bitmap[map]);
-                                offset = (BITS_PER_LONG * map) + block;
-                                offset *= pool->size;
-                                goto ready;
-                        }
-                }
+                if (page->offset < pool->allocation)
+                        goto ready;
         }
         page = pool_alloc_page(pool, GFP_ATOMIC);
         if (!page) {
@@ -333,10 +326,10 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
                 goto done;
         }
 
-        clear_bit(0, &page->bitmap[0]);
-        offset = 0;
  ready:
         page->in_use++;
+        offset = page->offset;
+        page->offset = *(int *)(page->vaddr + offset);
         retval = offset + page->vaddr;
         *handle = offset + page->dma;
 #ifdef  CONFIG_DEBUG_SLAB
@@ -379,7 +372,7 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 {
         struct dma_page *page;
         unsigned long flags;
-        int map, block;
+        unsigned int offset;
 
         page = pool_find_page(pool, dma);
         if (!page) {
@@ -393,13 +386,9 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
                 return;
         }
 
-        block = dma - page->dma;
-        block /= pool->size;
-        map = block / BITS_PER_LONG;
-        block %= BITS_PER_LONG;
-
+        offset = vaddr - page->vaddr;
 #ifdef  CONFIG_DEBUG_SLAB
-        if (((dma - page->dma) + (void *)page->vaddr) != vaddr) {
+        if ((dma - page->dma) != offset) {
                 if (pool->dev)
                         dev_err(pool->dev,
                                 "dma_pool_free %s, %p (bad vaddr)/%Lx\n",
@@ -410,28 +399,36 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
                                pool->name, vaddr, (unsigned long long)dma);
                 return;
         }
-        if (page->bitmap[map] & (1UL << block)) {
-                if (pool->dev)
-                        dev_err(pool->dev,
-                                "dma_pool_free %s, dma %Lx already free\n",
-                                pool->name, (unsigned long long)dma);
-                else
-                        printk(KERN_ERR
-                               "dma_pool_free %s, dma %Lx already free\n",
-                               pool->name, (unsigned long long)dma);
-                return;
+        {
+                unsigned int chain = page->offset;
+                while (chain < pool->allocation) {
+                        if (chain != offset) {
+                                chain = *(int *)(page->vaddr + chain);
+                                continue;
+                        }
+                        if (pool->dev)
+                                dev_err(pool->dev, "dma_pool_free %s, dma %Lx "
+                                        "already free\n", pool->name,
+                                        (unsigned long long)dma);
+                        else
+                                printk(KERN_ERR "dma_pool_free %s, dma %Lx "
+                                        "already free\n", pool->name,
+                                        (unsigned long long)dma);
+                        return;
+                }
         }
         memset(vaddr, POOL_POISON_FREED, pool->size);
 #endif
 
         spin_lock_irqsave(&pool->lock, flags);
         page->in_use--;
-        set_bit(block, &page->bitmap[map]);
+        *(int *)vaddr = page->offset;
+        page->offset = offset;
         if (waitqueue_active(&pool->waitq))
                 wake_up_locked(&pool->waitq);
         /*
          * Resist a temptation to do
-         *    if (!is_page_busy(bpp, page->bitmap)) pool_free_page(pool, page);
+         *    if (!is_page_busy(page)) pool_free_page(pool, page);
          * Better have a few empty pages hang around.
          */
         spin_unlock_irqrestore(&pool->lock, flags);