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Date: Thu, 23 Sep 2021 14:08:03 +0200 From: Jesper Dangaard Brouer <jbrouer@...hat.com> To: Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net, kuba@...nel.org Cc: brouer@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linuxarm@...neuler.org, hawk@...nel.org, ilias.apalodimas@...aro.org, jonathan.lemon@...il.com, alobakin@...me, willemb@...gle.com, cong.wang@...edance.com, pabeni@...hat.com, haokexin@...il.com, nogikh@...gle.com, elver@...gle.com, memxor@...il.com, edumazet@...gle.com, alexander.duyck@...il.com, dsahern@...il.com Subject: Re: [PATCH net-next 2/7] page_pool: support non-split page with PP_FLAG_PAGE_FRAG On 22/09/2021 11.41, Yunsheng Lin 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. > > Reviewed-by: Alexander Duyck <alexanderduyck@...com> > Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com> > --- > net/core/page_pool.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index a65bd7972e37..f7e71dcb6a2e 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -315,11 +315,14 @@ 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); > + I really don't like that you add one atomic_long_set operation per page alloc call. This is a fast-path for XDP use-cases, which you are ignoring as you drivers doesn't implement XDP. As I cannot ask you to run XDP benchmarks, I fortunately have some page_pool specific microbenchmarks you can run instead. I will ask you to provide before and after results from running these benchmarks [1] and [2]. [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c [2] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_cross_cpu.c How to use these module is documented here[3]: [3] https://prototype-kernel.readthedocs.io/en/latest/prototype-kernel/build-process.html > return page; > } > EXPORT_SYMBOL(page_pool_alloc_pages); > @@ -428,8 +431,7 @@ __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; This adds an atomic_long_read, even when PP_FLAG_PAGE_FRAG is not set. > > /* This allocator is optimized for the XDP mode that uses >
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