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[188.28.125.106]) by smtp.gmail.com with ESMTPSA id t21-20020a05640203d500b0043573c59ea0sm9758451edw.90.2022.06.28.11.59.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jun 2022 11:59:59 -0700 (PDT) From: Pavel Begunkov To: io-uring@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: "David S . Miller" , Jakub Kicinski , Jonathan Lemon , Willem de Bruijn , Jens Axboe , kernel-team@fb.com, Pavel Begunkov Subject: [RFC net-next v3 06/29] net: optimise bvec-based zc page referencing Date: Tue, 28 Jun 2022 19:56:28 +0100 Message-Id: <597c7c76624997d8933740e74e9b82d026bcfeff.1653992701.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.36.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Some users like io_uring can pass a bvec iterator to send and also can implement page pinning more efficiently. Add a ->msg_managed_data toogle in msghdr. When set, data pages are "managed" by upper layers, i.e. refcounted and pinned by the caller and will live at least until ->msg_ubuf is released. msghdr has to have non-NULL ->msg_ubuf and ->msg_iter should point to a bvec. Protocols supporting the feature will propagate it by setting SKBFL_MANAGED_FRAG_REFS, which means that the skb doesn't hold refs to its frag pages and only rely on ubuf_info lifetime gurantees. It should only be used with zerocopy skbs with ubuf_info set. It's allowed to convert skbs from managed to normal by calling skb_zcopy_downgrade_managed(). The function will take all needed page references and clear the flag. Signed-off-by: Pavel Begunkov --- include/linux/skbuff.h | 25 +++++++++++++++++++++++-- net/core/datagram.c | 7 ++++--- net/core/skbuff.c | 29 +++++++++++++++++++++++++++-- 3 files changed, 54 insertions(+), 7 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index eead3527bdaf..5407cfd9cb89 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -688,11 +688,16 @@ enum { SKBFL_PURE_ZEROCOPY = BIT(2), SKBFL_DONT_ORPHAN = BIT(3), + + /* page references are managed by the ubuf_info, so it's safe to + * use frags only up until ubuf_info is released + */ + SKBFL_MANAGED_FRAG_REFS = BIT(4), }; #define SKBFL_ZEROCOPY_FRAG (SKBFL_ZEROCOPY_ENABLE | SKBFL_SHARED_FRAG) #define SKBFL_ALL_ZEROCOPY (SKBFL_ZEROCOPY_FRAG | SKBFL_PURE_ZEROCOPY | \ - SKBFL_DONT_ORPHAN) + SKBFL_DONT_ORPHAN | SKBFL_MANAGED_FRAG_REFS) /* * The callback notifies userspace to release buffers when skb DMA is done in @@ -1809,6 +1814,11 @@ static inline bool skb_zcopy_pure(const struct sk_buff *skb) return skb_shinfo(skb)->flags & SKBFL_PURE_ZEROCOPY; } +static inline bool skb_zcopy_managed(const struct sk_buff *skb) +{ + return skb_shinfo(skb)->flags & SKBFL_MANAGED_FRAG_REFS; +} + static inline bool skb_pure_zcopy_same(const struct sk_buff *skb1, const struct sk_buff *skb2) { @@ -1883,6 +1893,14 @@ static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy_success) } } +void __skb_zcopy_downgrade_managed(struct sk_buff *skb); + +static inline void skb_zcopy_downgrade_managed(struct sk_buff *skb) +{ + if (unlikely(skb_zcopy_managed(skb))) + __skb_zcopy_downgrade_managed(skb); +} + static inline void skb_mark_not_on_list(struct sk_buff *skb) { skb->next = NULL; @@ -3491,7 +3509,10 @@ static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle) */ static inline void skb_frag_unref(struct sk_buff *skb, int f) { - __skb_frag_unref(&skb_shinfo(skb)->frags[f], skb->pp_recycle); + struct skb_shared_info *shinfo = skb_shinfo(skb); + + if (!skb_zcopy_managed(skb)) + __skb_frag_unref(&shinfo->frags[f], skb->pp_recycle); } /** diff --git a/net/core/datagram.c b/net/core/datagram.c index 5237cb533bb4..a93c05156f56 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -631,7 +631,6 @@ static int __zerocopy_sg_from_bvec(struct sock *sk, struct sk_buff *skb, copied += v.bv_len; truesize += PAGE_ALIGN(v.bv_len + v.bv_offset); - get_page(v.bv_page); skb_fill_page_desc(skb, frag++, v.bv_page, v.bv_offset, v.bv_len); bvec_iter_advance_single(from->bvec, &bi, v.bv_len); } @@ -660,11 +659,13 @@ static int __zerocopy_sg_from_bvec(struct sock *sk, struct sk_buff *skb, int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb, struct iov_iter *from, size_t length) { - int frag = skb_shinfo(skb)->nr_frags; + int frag; - if (iov_iter_is_bvec(from)) + if (skb_zcopy_managed(skb)) return __zerocopy_sg_from_bvec(sk, skb, from, length); + frag = skb_shinfo(skb)->nr_frags; + while (length && iov_iter_count(from)) { struct page *pages[MAX_SKB_FRAGS]; struct page *last_head = NULL; diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 5b35791064d1..71870def129c 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -666,11 +666,18 @@ static void skb_release_data(struct sk_buff *skb) &shinfo->dataref)) goto exit; - skb_zcopy_clear(skb, true); + if (skb_zcopy(skb)) { + bool skip_unref = shinfo->flags & SKBFL_MANAGED_FRAG_REFS; + + skb_zcopy_clear(skb, true); + if (skip_unref) + goto free_head; + } for (i = 0; i < shinfo->nr_frags; i++) __skb_frag_unref(&shinfo->frags[i], skb->pp_recycle); +free_head: if (shinfo->frag_list) kfree_skb_list(shinfo->frag_list); @@ -895,7 +902,10 @@ EXPORT_SYMBOL(skb_dump); */ void skb_tx_error(struct sk_buff *skb) { - skb_zcopy_clear(skb, true); + if (skb) { + skb_zcopy_downgrade_managed(skb); + skb_zcopy_clear(skb, true); + } } EXPORT_SYMBOL(skb_tx_error); @@ -1371,6 +1381,16 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, } EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream); +void __skb_zcopy_downgrade_managed(struct sk_buff *skb) +{ + int i; + + skb_shinfo(skb)->flags &= ~SKBFL_MANAGED_FRAG_REFS; + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) + skb_frag_ref(skb, i); +} +EXPORT_SYMBOL_GPL(__skb_zcopy_downgrade_managed); + static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig, gfp_t gfp_mask) { @@ -1688,6 +1708,8 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, BUG_ON(skb_shared(skb)); + skb_zcopy_downgrade_managed(skb); + size = SKB_DATA_ALIGN(size); if (skb_pfmemalloc(skb)) @@ -3484,6 +3506,8 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len) int pos = skb_headlen(skb); const int zc_flags = SKBFL_SHARED_FRAG | SKBFL_PURE_ZEROCOPY; + skb_zcopy_downgrade_managed(skb); + skb_shinfo(skb1)->flags |= skb_shinfo(skb)->flags & zc_flags; skb_zerocopy_clone(skb1, skb, 0); if (len < pos) /* Split line is inside header. */ @@ -3837,6 +3861,7 @@ int skb_append_pagefrags(struct sk_buff *skb, struct page *page, if (skb_can_coalesce(skb, i, page, offset)) { skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size); } else if (i < MAX_SKB_FRAGS) { + skb_zcopy_downgrade_managed(skb); get_page(page); skb_fill_page_desc(skb, i, page, offset, size); } else { -- 2.36.1