Re: [PATCH RFC net-next 1/3] net: page_pool: refactor dma_map into own function page_pool_dma_map
From: Ilias Apalodimas
Date: Wed Feb 24 2021 - 15:16:15 EST
On Wed, Feb 24, 2021 at 07:56:41PM +0100, Jesper Dangaard Brouer wrote:
>
In preparation for next patch, move the dma mapping into its own
>
function, as this will make it easier to follow the changes.
>
>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
>
---
>
net/core/page_pool.c | 49 +++++++++++++++++++++++++++++--------------------
>
1 file changed, 29 insertions(+), 20 deletions(-)
>
>
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>
index ad8b0707af04..50d52aa6fbeb 100644
>
--- a/net/core/page_pool.c
>
+++ b/net/core/page_pool.c
>
@@ -180,6 +180,31 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
>
pool->p.dma_dir);
>
}
>
>
+static struct page * page_pool_dma_map(struct page_pool *pool,
>
+ struct page *page)
>
+{
Why return a struct page* ?
boolean maybe?
>
+ dma_addr_t dma;
>
+
>
+ /* Setup DMA mapping: use 'struct page' area for storing DMA-addr
>
+ * since dma_addr_t can be either 32 or 64 bits and does not always fit
>
+ * into page private data (i.e 32bit cpu with 64bit DMA caps)
>
+ * This mapping is kept for lifetime of page, until leaving pool.
>
+ */
>
+ dma = dma_map_page_attrs(pool->p.dev, page, 0,
>
+ (PAGE_SIZE << pool->p.order),
>
+ pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
>
+ if (dma_mapping_error(pool->p.dev, dma)) {
>
+ put_page(page);
This is a bit confusing when reading it.
The name of the function should try to map the page and report a yes/no,
instead of trying to call put_page as well.
Can't we explicitly ask the user to call put_page() if the mapping failed?
A clear example is on patch 2/3, when on the first read I was convinced there
was a memory leak.
>
+ return NULL;
>
+ }
>
+ page->dma_addr = dma;
>
+
>
+ if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>
+ page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
>
+
>
+ return page;
>
+}
>
+
>
/* slow path */
>
noinline
>
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>
@@ -187,7 +212,6 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>
{
>
struct page *page;
>
gfp_t gfp = _gfp;
>
- dma_addr_t dma;
>
>
/* We could always set __GFP_COMP, and avoid this branch, as
>
* prep_new_page() can handle order-0 with __GFP_COMP.
>
@@ -211,27 +235,12 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>
if (!page)
>
return NULL;
>
>
- if (!(pool->p.flags & PP_FLAG_DMA_MAP))
>
- goto skip_dma_map;
>
-
>
- /* Setup DMA mapping: use 'struct page' area for storing DMA-addr
>
- * since dma_addr_t can be either 32 or 64 bits and does not always fit
>
- * into page private data (i.e 32bit cpu with 64bit DMA caps)
>
- * This mapping is kept for lifetime of page, until leaving pool.
>
- */
>
- dma = dma_map_page_attrs(pool->p.dev, page, 0,
>
- (PAGE_SIZE << pool->p.order),
>
- pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
>
- if (dma_mapping_error(pool->p.dev, dma)) {
>
- put_page(page);
>
- return NULL;
>
+ if (pool->p.flags & PP_FLAG_DMA_MAP) {
>
+ page = page_pool_dma_map(pool, page);
>
+ if (!page)
>
+ return NULL;
>
}
>
- page->dma_addr = dma;
>
-
>
- if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>
- page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
>
>
-skip_dma_map:
>
/* Track how many pages are held 'in-flight' */
>
pool->pages_state_hold_cnt++;
>
>
>
Thanks!
/Ilias