From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D9D57C3A5A2 for ; Fri, 23 Aug 2019 08:52:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABEC422CE3 for ; Fri, 23 Aug 2019 08:52:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393108AbfHWIwb (ORCPT ); Fri, 23 Aug 2019 04:52:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39038 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729690AbfHWIwa (ORCPT ); Fri, 23 Aug 2019 04:52:30 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7B3CF8980F2; Fri, 23 Aug 2019 08:52:30 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-255.rdu2.redhat.com [10.10.120.255]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6734117D08; Fri, 23 Aug 2019 08:52:29 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20190822.121207.731320146177703787.davem@davemloft.net> References: <20190822.121207.731320146177703787.davem@davemloft.net> <156647655350.10908.12081183247715153431.stgit@warthog.procyon.org.uk> To: David Miller Cc: dhowells@redhat.com, netdev@vger.kernel.org, linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net 0/9] rxrpc: Fix use of skb_cow_data() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <27347.1566550348.1@warthog.procyon.org.uk> Date: Fri, 23 Aug 2019 09:52:28 +0100 Message-ID: <27348.1566550348@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.67]); Fri, 23 Aug 2019 08:52:30 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org David Miller wrote: > Why don't you just do an skb_unshare() at the beginning when you know that > you'll need to do that? I was trying to defer any copying to process context rather than doing it in softirq context to spend less time in softirq context - plus that way I can use GFP_NOIO (kafs) or GFP_KERNEL (direct AF_RXRPC socket) rather than GFP_ATOMIC if the api supports it. I don't remember now why I used skb_cow_data() rather than skb_unshare() - but it was probably because the former leaves the sk_buff object itself intact, whereas the latter replaces it. I can switch to using skb_unshare() instead. Question for you: how likely is a newly received buffer, through a UDP socket, to be 'cloned'? David