page_pool: Refactor page_pool to enable fragmenting after allocation

This change is meant to permit a driver to perform "fragmenting" of the
page from within the driver instead of the current model which requires
pre-partitioning the page. The main motivation behind this is to support
use cases where the page will be split up by the driver after DMA instead
of before.

With this change it becomes possible to start using page pool to replace
some of the existing use cases where multiple references were being used
for a single page, but the number needed was unknown as the size could be
dynamic.

For example, with this code it would be possible to do something like
the following to handle allocation:
  page = page_pool_alloc_pages();
  if (!page)
    return NULL;
  page_pool_fragment_page(page, DRIVER_PAGECNT_BIAS_MAX);
  rx_buf->page = page;
  rx_buf->pagecnt_bias = DRIVER_PAGECNT_BIAS_MAX;

Then we would process a received buffer by handling it with:
  rx_buf->pagecnt_bias--;

Once the page has been fully consumed we could then flush the remaining
instances with:
  if (page_pool_defrag_page(page, rx_buf->pagecnt_bias))
    continue;
  page_pool_put_defragged_page(pool, page -1, !!budget);

The general idea is that we want to have the ability to allocate a page
with excess fragment count and then trim off the unneeded fragments.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 13 deletions

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index bd62c01a2ec3..e25d359d84d9 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -423,11 +423,6 @@ static __always_inline struct page *
 __page_pool_put_page(struct page_pool *pool, struct page *page,
 		     unsigned int dma_sync_size, bool allow_direct)
 {
-	/* It is not the last user for the page frag case */
-	if (pool->p.flags & PP_FLAG_PAGE_FRAG &&
-	    page_pool_atomic_sub_frag_count_return(page, 1))
-		return NULL;
-
 	/* This allocator is optimized for the XDP mode that uses
 	 * one-frame-per-page, but have fallbacks that act like the
 	 * regular page allocator APIs.
@@ -471,8 +466,8 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
 	return NULL;
 }
 
-void page_pool_put_page(struct page_pool *pool, struct page *page,
-			unsigned int dma_sync_size, bool allow_direct)
+void page_pool_put_defragged_page(struct page_pool *pool, struct page *page,
+				  unsigned int dma_sync_size, bool allow_direct)
 {
 	page = __page_pool_put_page(pool, page, dma_sync_size, allow_direct);
 	if (page && !page_pool_recycle_in_ring(pool, page)) {
@@ -480,7 +475,7 @@ void page_pool_put_page(struct page_pool *pool, struct page *page,
 		page_pool_return_page(pool, page);
 	}
 }
-EXPORT_SYMBOL(page_pool_put_page);
+EXPORT_SYMBOL(page_pool_put_defragged_page);
 
 /* Caller must not use data area after call, as this function overwrites it */
 void page_pool_put_page_bulk(struct page_pool *pool, void **data,
@@ -491,6 +486,10 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data,
 	for (i = 0; i < count; i++) {
 		struct page *page = virt_to_head_page(data[i]);
 
+		/* It is not the last user for the page frag case */
+		if (!page_pool_is_last_frag(pool, page))
+			continue;
+
 		page = __page_pool_put_page(pool, page, -1, false);
 		/* Approved for bulk recycling in ptr_ring cache */
 		if (page)
@@ -526,8 +525,7 @@ static struct page *page_pool_drain_frag(struct page_pool *pool,
 	long drain_count = BIAS_MAX - pool->frag_users;
 
 	/* Some user is still using the page frag */
-	if (likely(page_pool_atomic_sub_frag_count_return(page,
-							  drain_count)))
+	if (likely(page_pool_defrag_page(page, drain_count)))
 		return NULL;
 
 	if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
@@ -548,8 +546,7 @@ static void page_pool_free_frag(struct page_pool *pool)
 
 	pool->frag_page = NULL;
 
-	if (!page ||
-	    page_pool_atomic_sub_frag_count_return(page, drain_count))
+	if (!page || page_pool_defrag_page(page, drain_count))
 		return;
 
 	page_pool_return_page(pool, page);
@@ -588,7 +585,7 @@ frag_reset:
 		pool->frag_users = 1;
 		*offset = 0;
 		pool->frag_offset = size;
-		page_pool_set_frag_count(page, BIAS_MAX);
+		page_pool_fragment_page(page, BIAS_MAX);
 		return page;
 	}