From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935127Ab3E2HhA (ORCPT ); Wed, 29 May 2013 03:37:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59526 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935097Ab3E2Hg7 (ORCPT ); Wed, 29 May 2013 03:36:59 -0400 Message-ID: <51A5B011.7000101@redhat.com> Date: Wed, 29 May 2013 03:36:49 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Eric Dumazet CC: atomlin@redhat.com, netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, pshelar@nicira.com, mst@redhat.com, alexander.h.duyck@intel.com, aquini@redhat.com, sergei.shtylyov@cogentembedded.com, linux-kernel@vger.kernel.org Subject: Re: [Patch v2] skbuff: Hide GFP_ATOMIC page allocation failures for dropped packets References: <1369599557-22677-1-git-send-email-atomlin@redhat.com> <51A39A3F.8080903@redhat.com> <1369693520.3301.477.camel@edumazet-glaptop> In-Reply-To: <1369693520.3301.477.camel@edumazet-glaptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/27/2013 06:25 PM, Eric Dumazet wrote: > On Mon, 2013-05-27 at 13:39 -0400, Rik van Riel wrote: >> Yes please. Getting memory management bug reports for >> dropped network packets got old years ago. Lets get >> rid of those messages. > > I am only wondering why this path has anything needing special > attention, over thousands of kmalloc() like call sites in the kernel. There are a few special things about the network code: 1) network packets can arrive extremely fast, in large batches 2) the network code cannot wait for the VM to free memory (GFP_ATOMIC) Other allocations tend to be done less at a time, and/or allow the VM to free up memory before proceeding. > If mm allocation warnings are useless, just make __GFP_NOWARN the > default, and save us thousand of patches (adding the __GFP_NOWARN > everywhere) > > Truth is : some network drivers don't deal very well with allocation > errors. mlx4 for example absolutely wants order-2 pages in RX path, with > no fallback to order-0 pages. Network protocols and network applications tend to deal with packet loss by retransmitting data, though. Also, once all the data from one of those order-2 page buffers has been delivered or forwarded, that buffer becomes available to subsequent network packets. Other allocations tend not to free & reuse their memory as quickly as the network stack. > So I am not against this patch, but I can not really acknowledge it, > sorry. > > >