From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [bpf-next PATCH 4/7] net: do_tcp_sendpages flag to avoid SKBTX_SHARED_FRAG Date: Fri, 12 Jan 2018 12:10:45 -0800 Message-ID: <1515787845.131759.46.camel@gmail.com> References: <20180112175029.21531.54693.stgit@john-Precision-Tower-5810> <20180112181055.21531.95322.stgit@john-Precision-Tower-5810> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, kafai@fb.com To: John Fastabend , borkmann@iogearbox.net, ast@kernel.org Return-path: Received: from mail-pg0-f68.google.com ([74.125.83.68]:33615 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965121AbeALUKr (ORCPT ); Fri, 12 Jan 2018 15:10:47 -0500 Received: by mail-pg0-f68.google.com with SMTP id i196so5269740pgd.0 for ; Fri, 12 Jan 2018 12:10:47 -0800 (PST) In-Reply-To: <20180112181055.21531.95322.stgit@john-Precision-Tower-5810> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2018-01-12 at 10:10 -0800, John Fastabend wrote: > When calling do_tcp_sendpages() from in kernel and we know the data > has no references from user side we can omit SKBTX_SHARED_FRAG flag. > This patch adds an internal flag, NO_SKBTX_SHARED_FRAG that can be used > to omit setting SKBTX_SHARED_FRAG. > > Signed-off-by: John Fastabend > --- > include/linux/socket.h | 1 + > net/ipv4/tcp.c | 4 +++- > 2 files changed, 4 insertions(+), 1 deletion(-) > > diff --git a/include/linux/socket.h b/include/linux/socket.h > index 9286a5a..add9360 100644 > --- a/include/linux/socket.h > +++ b/include/linux/socket.h > @@ -287,6 +287,7 @@ struct ucred { > #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */ > #define MSG_BATCH 0x40000 /* sendmmsg(): more messages coming */ > #define MSG_EOF MSG_FIN > +#define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */ > > #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */ > #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */ > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index 7ac583a..56c6f49 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -995,7 +995,9 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset, > get_page(page); > skb_fill_page_desc(skb, i, page, offset, copy); > } > - skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG; > + > + if (!(flags & MSG_NO_SHARED_FRAGS)) > + skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG; > > skb->len += copy; > skb->data_len += copy; What would prevent user space from using this flag ?