On 2021/9/23 20:08, Jesper Dangaard Brouer wrote:
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@fb.com> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.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/benc...
[2] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/benc...
How to use these module is documented here[3]: [3] https://prototype-kernel.readthedocs.io/en/latest/prototype-kernel/build-pro...
Will running these benchmarks to see if any performance overhead noticable here, thanks for the benchmarks.
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.
The point here is to have consistent handling for both PP_FLAG_PAGE_FRAG and non-PP_FLAG_PAGE_FRAG case in the following patch. As the page->_refcount is accessed in "page_ref_count(page) == 1" checking in __page_pool_put_page(), and page->pp_frag_count is most likely in the same cache line as the page->_refcount, So I am not expecting a noticable overhead here. Anyway, will use the above benchmarks as an example to verify it.
/* This allocator is optimized for the XDP mode that uses
.