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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , David Ahern , Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Menglong Dong Subject: [PATCH net-next 01/17] net: Copy slab data for sendmsg(MSG_SPLICE_PAGES) Date: Fri, 16 Jun 2023 17:12:44 +0100 Message-ID: <20230616161301.622169-2-dhowells@redhat.com> In-Reply-To: <20230616161301.622169-1-dhowells@redhat.com> References: <20230616161301.622169-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768877843486819552?= X-GMAIL-MSGID: =?utf-8?q?1768877843486819552?= If sendmsg() is passed MSG_SPLICE_PAGES and is given a buffer that contains some data that's resident in the slab, copy it rather than returning EIO. This can be made use of by a number of drivers in the kernel, including: iwarp, ceph/rds, dlm, nvme, ocfs2, drdb. It could also be used by iscsi, rxrpc, sunrpc, cifs and probably others. skb_splice_from_iter() is given it's own fragment allocator as page_frag_alloc_align() can't be used because it does no locking to prevent parallel callers from racing. alloc_skb_frag() uses a separate folio for each cpu and locks to the cpu whilst allocating, reenabling cpu migration around folio allocation. This could allocate a whole page instead for each fragment to be copied, as alloc_skb_with_frags() would do instead, but that would waste a lot of space (most of the fragments look like they're going to be small). This allows an entire message that consists of, say, a protocol header or two, a number of pages of data and a protocol footer to be sent using a single call to sock_sendmsg(). The callers could be made to copy the data into fragments before calling sendmsg(), but that then penalises them if MSG_SPLICE_PAGES gets ignored. Signed-off-by: David Howells cc: Alexander Duyck cc: Eric Dumazet cc: "David S. Miller" cc: David Ahern cc: Jakub Kicinski cc: Paolo Abeni cc: Jens Axboe cc: Matthew Wilcox cc: Menglong Dong cc: netdev@vger.kernel.org --- include/linux/skbuff.h | 5 ++ net/core/skbuff.c | 172 ++++++++++++++++++++++++++++++++++++++++- 2 files changed, 174 insertions(+), 3 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 91ed66952580..0ba776cd9be8 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -5037,6 +5037,11 @@ static inline void skb_mark_for_recycle(struct sk_buff *skb) #endif } +void *alloc_skb_frag(size_t fragsz, gfp_t gfp); +void *copy_skb_frag(const void *s, size_t len, gfp_t gfp); +ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, + ssize_t maxsize, gfp_t gfp); + ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, ssize_t maxsize, gfp_t gfp); diff --git a/net/core/skbuff.c b/net/core/skbuff.c index fee2b1c105fe..9bd8d6bf6c21 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6755,6 +6755,146 @@ nodefer: __kfree_skb(skb); smp_call_function_single_async(cpu, &sd->defer_csd); } +struct skb_splice_frag_cache { + struct folio *folio; + void *virt; + unsigned int offset; + /* we maintain a pagecount bias, so that we dont dirty cache line + * containing page->_refcount every time we allocate a fragment. + */ + unsigned int pagecnt_bias; + bool pfmemalloc; +}; + +static DEFINE_PER_CPU(struct skb_splice_frag_cache, skb_splice_frag_cache); + +/** + * alloc_skb_frag - Allocate a page fragment for using in a socket + * @fragsz: The size of fragment required + * @gfp: Allocation flags + */ +void *alloc_skb_frag(size_t fragsz, gfp_t gfp) +{ + struct skb_splice_frag_cache *cache; + struct folio *folio, *spare = NULL; + size_t offset, fsize; + void *p; + + if (WARN_ON_ONCE(fragsz == 0)) + fragsz = 1; + + cache = get_cpu_ptr(&skb_splice_frag_cache); +reload: + folio = cache->folio; + offset = cache->offset; +try_again: + if (fragsz > offset) + goto insufficient_space; + + /* Make the allocation. */ + cache->pagecnt_bias--; + offset = ALIGN_DOWN(offset - fragsz, SMP_CACHE_BYTES); + cache->offset = offset; + p = cache->virt + offset; + put_cpu_ptr(skb_splice_frag_cache); + if (spare) + folio_put(spare); + return p; + +insufficient_space: + /* See if we can refurbish the current folio. */ + if (!folio || !folio_ref_sub_and_test(folio, cache->pagecnt_bias)) + goto get_new_folio; + if (unlikely(cache->pfmemalloc)) { + __folio_put(folio); + goto get_new_folio; + } + + fsize = folio_size(folio); + if (unlikely(fragsz > fsize)) + goto frag_too_big; + + /* OK, page count is 0, we can safely set it */ + folio_set_count(folio, PAGE_FRAG_CACHE_MAX_SIZE + 1); + + /* Reset page count bias and offset to start of new frag */ + cache->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; + offset = fsize; + goto try_again; + +get_new_folio: + if (!spare) { + cache->folio = NULL; + put_cpu_ptr(&skb_splice_frag_cache); + +#if PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE + spare = folio_alloc(gfp | __GFP_NOWARN | __GFP_NORETRY | + __GFP_NOMEMALLOC, + PAGE_FRAG_CACHE_MAX_ORDER); + if (!spare) +#endif + spare = folio_alloc(gfp, 0); + if (!spare) + return NULL; + + cache = get_cpu_ptr(&skb_splice_frag_cache); + /* We may now be on a different cpu and/or someone else may + * have refilled it + */ + cache->pfmemalloc = folio_is_pfmemalloc(spare); + if (cache->folio) + goto reload; + } + + cache->folio = spare; + cache->virt = folio_address(spare); + folio = spare; + spare = NULL; + + /* Even if we own the page, we do not use atomic_set(). This would + * break get_page_unless_zero() users. + */ + folio_ref_add(folio, PAGE_FRAG_CACHE_MAX_SIZE); + + /* Reset page count bias and offset to start of new frag */ + cache->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; + offset = folio_size(folio); + goto try_again; + +frag_too_big: + /* + * The caller is trying to allocate a fragment with fragsz > PAGE_SIZE + * but the cache isn't big enough to satisfy the request, this may + * happen in low memory conditions. We don't release the cache page + * because it could make memory pressure worse so we simply return NULL + * here. + */ + cache->offset = offset; + put_cpu_ptr(&skb_splice_frag_cache); + if (spare) + folio_put(spare); + return NULL; +} +EXPORT_SYMBOL(alloc_skb_frag); + +/** + * copy_skb_frag - Copy data into a page fragment. + * @s: The data to copy + * @len: The size of the data + * @gfp: Allocation flags + */ +void *copy_skb_frag(const void *s, size_t len, gfp_t gfp) +{ + void *p; + + p = alloc_skb_frag(len, gfp); + if (!p) + return NULL; + + return memcpy(p, s, len); +} +EXPORT_SYMBOL(copy_skb_frag); + static void skb_splice_csum_page(struct sk_buff *skb, struct page *page, size_t offset, size_t len) { @@ -6808,17 +6948,43 @@ ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, break; } + if (space == 0 && + !skb_can_coalesce(skb, skb_shinfo(skb)->nr_frags, + pages[0], off)) { + iov_iter_revert(iter, len); + break; + } + i = 0; do { struct page *page = pages[i++]; size_t part = min_t(size_t, PAGE_SIZE - off, len); - - ret = -EIO; - if (WARN_ON_ONCE(!sendpage_ok(page))) + bool put = false; + + if (PageSlab(page)) { + const void *p; + void *q; + + p = kmap_local_page(page); + q = copy_skb_frag(p + off, part, gfp); + kunmap_local(p); + if (!q) { + iov_iter_revert(iter, len); + ret = -ENOMEM; + goto out; + } + page = virt_to_page(q); + off = offset_in_page(q); + put = true; + } else if (WARN_ON_ONCE(!sendpage_ok(page))) { + ret = -EIO; goto out; + } ret = skb_append_pagefrags(skb, page, off, part, frag_limit); + if (put) + put_page(page); if (ret < 0) { iov_iter_revert(iter, len); goto out;