[PATCH 1/2] mm/dmapool: replace linked list with xarray

kbusch
2022-04-28T20:27:22Z

From: Keith Busch <kbusch@kernel.org>

Store the cached dma pool pages in an xarray instead of a linked list.
This allows constant lookup time to free the page, lockless iteration
while displaying the attributes, and frees up space in 'struct dma_page'.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
mm/dmapool.c | 39 ++++++++++++++++-----------------------
1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index a7eb5d0eb2da..ac93f58d4654 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -35,13 +35,14 @@
#include <linux/string.h>
#include <linux/types.h>
#include <linux/wait.h>
+#include <linux/xarray.h>

#if defined(CONFIG_DEBUG_SLAB) || defined(CONFIG_SLUB_DEBUG_ON)
#define DMAPOOL_DEBUG 1
#endif

struct dma_pool { /* the pool */
- struct list_head page_list;
+ struct xarray pages;
spinlock_t lock;
size_t size;
struct device *dev;
@@ -52,7 +53,6 @@ struct dma_pool { /* the pool */
};

struct dma_page { /* cacheable header for 'allocation' bytes */
- struct list_head page_list;
void *vaddr;
dma_addr_t dma;
unsigned int in_use;
@@ -81,13 +81,12 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
list_for_each_entry(pool, &dev->dma_pools, pools) {
unsigned pages = 0;
unsigned blocks = 0;
+ unsigned long i;

- spin_lock_irq(&pool->lock);
- list_for_each_entry(page, &pool->page_list, page_list) {
+ xa_for_each(&pool->pages, i, page) {
pages++;
blocks += page->in_use;
}
- spin_unlock_irq(&pool->lock);

/* per-pool info, no real statistics yet */
temp = scnprintf(next, size, "%-16s %4u %4zu %4zu %2u\n",
@@ -160,7 +159,7 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,

retval->dev = dev;

- INIT_LIST_HEAD(&retval->page_list);
+ xa_init(&retval->pages);
spin_lock_init(&retval->lock);
retval->size = size;
retval->boundary = boundary;
@@ -252,7 +251,6 @@ static void pool_free_page(struct dma_pool *pool, struct dma_page *page)
memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
#endif
dma_free_coherent(pool->dev, pool->allocation, page->vaddr, dma);
- list_del(&page->page_list);
kfree(page);
}

@@ -266,8 +264,9 @@ static void pool_free_page(struct dma_pool *pool, struct dma_page *page)
*/
void dma_pool_destroy(struct dma_pool *pool)
{
- struct dma_page *page, *tmp;
+ struct dma_page *page;
bool empty = false;
+ unsigned long i;

if (unlikely(!pool))
return;
@@ -282,7 +281,8 @@ void dma_pool_destroy(struct dma_pool *pool)
device_remove_file(pool->dev, &dev_attr_pools);
mutex_unlock(&pools_reg_lock);

- list_for_each_entry_safe(page, tmp, &pool->page_list, page_list) {
+ xa_for_each(&pool->pages, i, page) {
+ xa_erase(&pool->pages, i);
if (is_page_busy(page)) {
if (pool->dev)
dev_err(pool->dev, "%s %s, %p busy\n", __func__,
@@ -291,12 +291,12 @@ void dma_pool_destroy(struct dma_pool *pool)
pr_err("%s %s, %p busy\n", __func__,
pool->name, page->vaddr);
/* leak the still-in-use consistent memory */
- list_del(&page->page_list);
kfree(page);
} else
pool_free_page(pool, page);
}

+ xa_destroy(&pool->pages);
kfree(pool);
}
EXPORT_SYMBOL(dma_pool_destroy);
@@ -316,13 +316,14 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
{
unsigned long flags;
struct dma_page *page;
+ unsigned long i;
size_t offset;
void *retval;

might_alloc(mem_flags);

spin_lock_irqsave(&pool->lock, flags);
- list_for_each_entry(page, &pool->page_list, page_list) {
+ xa_for_each(&pool->pages, i, page) {
if (page->offset < pool->allocation)
goto ready;
}
@@ -334,9 +335,9 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
if (!page)
return NULL;

+ xa_store(&pool->pages, page->vaddr, page, mem_flags);
spin_lock_irqsave(&pool->lock, flags);

- list_add(&page->page_list, &pool->page_list);
ready:
page->in_use++;
offset = page->offset;
@@ -379,17 +380,9 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
}
EXPORT_SYMBOL(dma_pool_alloc);

-static struct dma_page *pool_find_page(struct dma_pool *pool, dma_addr_t dma)
+static struct dma_page *pool_find_page(struct dma_pool *pool, unsigned long vaddr)
{
- struct dma_page *page;
-
- list_for_each_entry(page, &pool->page_list, page_list) {
- if (dma < page->dma)
- continue;
- if ((dma - page->dma) < pool->allocation)
- return page;
- }
- return NULL;
+ return xa_load(pool->pages, vaddr & ~(pool->allocation - 1));
}

/**
@@ -408,7 +401,7 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
unsigned int offset;

spin_lock_irqsave(&pool->lock, flags);
- page = pool_find_page(pool, dma);
+ page = pool_find_page(pool, vaddr);
if (!page) {
spin_unlock_irqrestore(&pool->lock, flags);
if (pool->dev)
--
2.30.2