Messages in this thread | | | Subject | Re: [PATCH net-next 1/2] page_pool: support non-split page with PP_FLAG_PAGE_FRAG | From | Yunsheng Lin <> | Date | Tue, 31 Aug 2021 14:14:33 +0800 |
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On 2021/8/30 23:05, Alexander Duyck wrote: > On Sun, Aug 29, 2021 at 6:19 PM Yunsheng Lin <linyunsheng@huawei.com> wrote: >> >> Currently when PP_FLAG_PAGE_FRAG is set, the caller is not >> expected to call page_pool_alloc_pages() directly because of >> the PP_FLAG_PAGE_FRAG checking in __page_pool_put_page(). >> >> The patch removes the above checking to enable non-split page >> support when PP_FLAG_PAGE_FRAG is set. >> >> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> >> --- >> include/net/page_pool.h | 6 ++++++ >> net/core/page_pool.c | 12 +++++++----- >> 2 files changed, 13 insertions(+), 5 deletions(-) >> >> diff --git a/include/net/page_pool.h b/include/net/page_pool.h >> index a408240..2ad0706 100644 >> --- a/include/net/page_pool.h >> +++ b/include/net/page_pool.h >> @@ -238,6 +238,9 @@ static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr) >> >> static inline void page_pool_set_frag_count(struct page *page, long nr) >> { >> + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) >> + return; >> + >> atomic_long_set(&page->pp_frag_count, nr); >> } >> >> @@ -246,6 +249,9 @@ static inline long page_pool_atomic_sub_frag_count_return(struct page *page, >> { >> long ret; >> >> + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) >> + return 0; >> + >> /* As suggested by Alexander, atomic_long_read() may cover up the >> * reference count errors, so avoid calling atomic_long_read() in >> * the cases of freeing or draining the page_frags, where we would >> diff --git a/net/core/page_pool.c b/net/core/page_pool.c >> index 1a69784..ba9f14d 100644 >> --- a/net/core/page_pool.c >> +++ b/net/core/page_pool.c >> @@ -313,11 +313,14 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp) >> >> /* Fast-path: Get a page from cache */ >> page = __page_pool_get_cached(pool); >> - if (page) >> - return page; >> >> /* Slow-path: cache empty, do real allocation */ >> - page = __page_pool_alloc_pages_slow(pool, gfp); >> + if (!page) >> + page = __page_pool_alloc_pages_slow(pool, gfp); >> + >> + if (likely(page)) >> + page_pool_set_frag_count(page, 1); >> + >> return page; >> } >> EXPORT_SYMBOL(page_pool_alloc_pages); >> @@ -426,8 +429,7 @@ __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)) >> + if (page_pool_atomic_sub_frag_count_return(page, 1)) >> return NULL; > > Isn't this going to have a negative performance impact on page pool > pages in general? Essentially you are adding an extra atomic operation > for all the non-frag pages. > > It would work better if this was doing a check against 1 to determine > if it is okay for this page to be freed here and only if the check > fails then you perform the atomic sub_return.
The page_pool_atomic_sub_frag_count_return() has added the optimization to not do the atomic sub_return when the caller is the last user of the page, see page_pool_atomic_sub_frag_count_return():
/* As suggested by Alexander, atomic_long_read() may cover up the * reference count errors, so avoid calling atomic_long_read() in * the cases of freeing or draining the page_frags, where we would * not expect it to match or that are slowpath anyway. */ if (__builtin_constant_p(nr) && atomic_long_read(&page->pp_frag_count) == nr) return 0;
So the check against 1 is not needed here?
> . >
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