* page allocated from page pool. Page splitting enables memory saving and thus
* avoids TLB/cache miss for data access, but there also is some cost to
* implement page splitting, mainly some cache line dirtying/bouncing for
- * 'struct page' and atomic operation for page->pp_frag_count.
+ * 'struct page' and atomic operation for page->pp_ref_count.
*
* The API keeps track of in-flight pages, in order to let API users know when
* it is safe to free a page_pool object, the API users must call
return pool->p.dma_dir;
}
-/* pp_frag_count represents the number of writers who can update the page
- * either by updating skb->data or via DMA mappings for the device.
- * We can't rely on the page refcnt for that as we don't know who might be
- * holding page references and we can't reliably destroy or sync DMA mappings
- * of the fragments.
+/**
+ * page_pool_fragment_page() - split a fresh page into fragments
+ * @page: page to split
+ * @nr: references to set
+ *
+ * pp_ref_count represents the number of outstanding references to the page,
+ * which will be freed using page_pool APIs (rather than page allocator APIs
+ * like put_page()). Such references are usually held by page_pool-aware
+ * objects like skbs marked for page pool recycling.
*
- * When pp_frag_count reaches 0 we can either recycle the page if the page
- * refcnt is 1 or return it back to the memory allocator and destroy any
- * mappings we have.
+ * This helper allows the caller to take (set) multiple references to a
+ * freshly allocated page. The page must be freshly allocated (have a
+ * pp_ref_count of 1). This is commonly done by drivers and
+ * "fragment allocators" to save atomic operations - either when they know
+ * upfront how many references they will need; or to take MAX references and
+ * return the unused ones with a single atomic dec(), instead of performing
+ * multiple atomic inc() operations.
*/
static inline void page_pool_fragment_page(struct page *page, long nr)
{
- atomic_long_set(&page->pp_frag_count, nr);
+ atomic_long_set(&page->pp_ref_count, nr);
}
-static inline long page_pool_defrag_page(struct page *page, long nr)
+static inline long page_pool_unref_page(struct page *page, long nr)
{
long ret;
- /* If nr == pp_frag_count then we have cleared all remaining
+ /* If nr == pp_ref_count then we have cleared all remaining
* references to the page:
* 1. 'n == 1': no need to actually overwrite it.
* 2. 'n != 1': overwrite it with one, which is the rare case
- * for pp_frag_count draining.
+ * for pp_ref_count draining.
*
* The main advantage to doing this is that not only we avoid a atomic
* update, as an atomic_read is generally a much cheaper operation than
* an atomic update, especially when dealing with a page that may be
- * partitioned into only 2 or 3 pieces; but also unify the pp_frag_count
+ * referenced by only 2 or 3 users; but also unify the pp_ref_count
* handling by ensuring all pages have partitioned into only 1 piece
* initially, and only overwrite it when the page is partitioned into
* more than one piece.
*/
- if (atomic_long_read(&page->pp_frag_count) == nr) {
+ if (atomic_long_read(&page->pp_ref_count) == nr) {
/* As we have ensured nr is always one for constant case using
* the BUILD_BUG_ON(), only need to handle the non-constant case
- * here for pp_frag_count draining, which is a rare case.
+ * here for pp_ref_count draining, which is a rare case.
*/
BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1);
if (!__builtin_constant_p(nr))
- atomic_long_set(&page->pp_frag_count, 1);
+ atomic_long_set(&page->pp_ref_count, 1);
return 0;
}
- ret = atomic_long_sub_return(nr, &page->pp_frag_count);
+ ret = atomic_long_sub_return(nr, &page->pp_ref_count);
WARN_ON(ret < 0);
- /* We are the last user here too, reset pp_frag_count back to 1 to
+ /* We are the last user here too, reset pp_ref_count back to 1 to
* ensure all pages have been partitioned into 1 piece initially,
* this should be the rare case when the last two fragment users call
- * page_pool_defrag_page() currently.
+ * page_pool_unref_page() currently.
*/
if (unlikely(!ret))
- atomic_long_set(&page->pp_frag_count, 1);
+ atomic_long_set(&page->pp_ref_count, 1);
return ret;
}
-static inline bool page_pool_is_last_frag(struct page *page)
+static inline bool page_pool_is_last_ref(struct page *page)
{
- /* If page_pool_defrag_page() returns 0, we were the last user */
- return page_pool_defrag_page(page, 1) == 0;
+ /* If page_pool_unref_page() returns 0, we were the last user */
+ return page_pool_unref_page(page, 1) == 0;
}
/**
* allow registering MEM_TYPE_PAGE_POOL, but shield linker.
*/
#ifdef CONFIG_PAGE_POOL
- if (!page_pool_is_last_frag(page))
+ if (!page_pool_is_last_ref(page))
return;
- page_pool_put_defragged_page(pool, page, dma_sync_size, allow_direct);
+ page_pool_put_unrefed_page(pool, page, dma_sync_size, allow_direct);
#endif
}
return NULL;
}
-void page_pool_put_defragged_page(struct page_pool *pool, struct page *page,
- unsigned int dma_sync_size, bool allow_direct)
+void page_pool_put_unrefed_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)) {
page_pool_return_page(pool, page);
}
}
-EXPORT_SYMBOL(page_pool_put_defragged_page);
+EXPORT_SYMBOL(page_pool_put_unrefed_page);
/**
* page_pool_put_page_bulk() - release references on multiple pages
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(page))
+ if (!page_pool_is_last_ref(page))
continue;
page = __page_pool_put_page(pool, page, -1, false);
long drain_count = BIAS_MAX - pool->frag_users;
/* Some user is still using the page frag */
- if (likely(page_pool_defrag_page(page, drain_count)))
+ if (likely(page_pool_unref_page(page, drain_count)))
return NULL;
if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
pool->frag_page = NULL;
- if (!page || page_pool_defrag_page(page, drain_count))
+ if (!page || page_pool_unref_page(page, drain_count))
return;
page_pool_return_page(pool, page);
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