From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: Proposed linux kernel changes : scaling tcp/ip stack Date: Wed, 16 Jun 2010 11:10:07 +0200 Message-ID: <87fx0nwdg0.fsf@basil.nowhere.org> References: <1275556440.2456.19.camel@edumazet-laptop> <97746864-ED54-4A12-AFE7-752AA6E41CDD@earthlink.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , netdev@vger.kernel.org To: Mitchell Erblich Return-path: Received: from one.firstfloor.org ([213.235.205.2]:51329 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752931Ab0FPJKM (ORCPT ); Wed, 16 Jun 2010 05:10:12 -0400 In-Reply-To: <97746864-ED54-4A12-AFE7-752AA6E41CDD@earthlink.net> (Mitchell Erblich's message of "Tue\, 15 Jun 2010 20\:11\:42 -0700") Sender: netdev-owner@vger.kernel.org List-ID: Mitchell Erblich writes: > > Summary: Don't use last free pages for TCP ACKs with GFP_ATOMIC for our > sk buf allocs. 1 line change in tcp_output.c with a new gfp.h arg, and a change > in the generic kernel. TBD. > > This change should have no effect with normal available kernel mem allocs. > > Assuming memory pressure ( WAITING for clean memory) we should be allocating > our last pages for input skbufs and not for xmit allocs. How about you instrument a kernel and measure if this really happens frequently under reasonable loads? That is you can probably use the existing dropped page counters in netstat Stephen added some time ago. Since soft irqs cannot really wait exhausted GFP_ATOMIC would normally lead to dropped packets. FWIW I am not aware of any serious dropped packets problem on normal loads. Running a kernel with nearly zero free memory is dangerous anyways -- pretty much any kernel service can fail arbitarily -- if this happened frequently I suspect we would need generic VM solution for it. -Andi -- ak@linux.intel.com -- Speaking for myself only.