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Change dmapool free block management
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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 <[email protected]>
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Matthew Wilcox committed Dec 4, 2007
1 parent 6182a09 commit a35a345
Showing 1 changed file with 58 additions and 61 deletions.
119 changes: 58 additions & 61 deletions mm/dmapool.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -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;
Expand All @@ -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)
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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) {
Expand All @@ -186,43 +189,46 @@ 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;
}
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)
Expand Down Expand Up @@ -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",
Expand Down Expand Up @@ -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) {
Expand All @@ -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
Expand Down Expand Up @@ -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) {
Expand All @@ -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",
Expand All @@ -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);
Expand Down

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