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Subject[PATCH rfc v2 4/5] page_pool: support page frag API for page pool
Date
Currently each desc use a whole page to do ping-pong page
reusing in most driver. As the page pool has support page
recycling based on elevated refcnt, it makes sense to add
a page frag API in page pool to split a page to different
frag to serve multi descriptions.

This means a huge memory saving for kernel with page size of
64K, as a page can be used by 32 descriptions with 2k buffer
size, comparing to each desc using one page currently.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
include/net/page_pool.h | 14 ++++++++++++++
net/core/page_pool.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 63 insertions(+)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index f0e708d..06a5e43 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -80,6 +80,7 @@ struct page_pool_params {
enum dma_data_direction dma_dir; /* DMA mapping direction */
unsigned int max_len; /* max DMA sync memory size */
unsigned int offset; /* DMA addr offset */
+ unsigned int frag_size;
};

struct page_pool {
@@ -91,6 +92,8 @@ struct page_pool {
unsigned long defer_warn;

u32 pages_state_hold_cnt;
+ unsigned int frag_offset;
+ struct page *frag_page;

/*
* Data structure for allocation side
@@ -140,6 +143,17 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
return page_pool_alloc_pages(pool, gfp);
}

+struct page *page_pool_alloc_frag(struct page_pool *pool,
+ unsigned int *offset, gfp_t gfp);
+
+static inline struct page *page_pool_dev_alloc_frag(struct page_pool *pool,
+ unsigned int *offset)
+{
+ gfp_t gfp = (GFP_ATOMIC | __GFP_NOWARN);
+
+ return page_pool_alloc_frag(pool, offset, gfp);
+}
+
/* get the stored dma direction. A driver might decide to treat this locally and
* avoid the extra cache line from page_pool to determine the direction
*/
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index a87cbe1..b787033 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -350,6 +350,53 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
}
EXPORT_SYMBOL(page_pool_alloc_pages);

+struct page *page_pool_alloc_frag(struct page_pool *pool,
+ unsigned int *offset, gfp_t gfp)
+{
+ unsigned int frag_offset = pool->frag_offset;
+ unsigned int frag_size = pool->p.frag_size;
+ struct page *frag_page = pool->frag_page;
+ unsigned int max_len = pool->p.max_len;
+
+ if (!frag_page || frag_offset + frag_size > max_len) {
+ frag_page = page_pool_alloc_pages(pool, gfp);
+ if (unlikely(!frag_page)) {
+ pool->frag_page = NULL;
+ return NULL;
+ }
+
+ pool->frag_page = frag_page;
+ frag_offset = 0;
+
+ page_pool_sub_bias(pool, frag_page,
+ max_len / frag_size - 1);
+ }
+
+ *offset = frag_offset;
+ pool->frag_offset = frag_offset + frag_size;
+
+ return frag_page;
+}
+EXPORT_SYMBOL(page_pool_alloc_frag);
+
+static void page_pool_empty_frag(struct page_pool *pool)
+{
+ unsigned int frag_offset = pool->frag_offset;
+ unsigned int frag_size = pool->p.frag_size;
+ struct page *frag_page = pool->frag_page;
+ unsigned int max_len = pool->p.max_len;
+
+ if (!frag_page)
+ return;
+
+ while (frag_offset + frag_size <= max_len) {
+ page_pool_put_full_page(pool, frag_page, false);
+ frag_offset += frag_size;
+ }
+
+ pool->frag_page = NULL;
+}
+
/* Calculate distance between two u32 values, valid if distance is below 2^(31)
* https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
*/
@@ -670,6 +717,8 @@ void page_pool_destroy(struct page_pool *pool)
if (!page_pool_put(pool))
return;

+ page_pool_empty_frag(pool);
+
if (!page_pool_release(pool))
return;

--
2.7.4
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