From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755411Ab2AIHMh (ORCPT ); Mon, 9 Jan 2012 02:12:37 -0500 Received: from ozlabs.org ([203.10.76.45]:53632 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754296Ab2AIHMf convert rfc822-to-8bit (ORCPT ); Mon, 9 Jan 2012 02:12:35 -0500 From: Rusty Russell To: Mike Waychison Cc: "Michael S. Tsirkin" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [RFC PATCH v1 2/2] virtio_net: Don't disable napi on low memory. In-Reply-To: References: <20120104225223.18184.1537.stgit@mike2.sea.corp.google.com> <20120104225237.18184.71853.stgit@mike2.sea.corp.google.com> <87y5tnat2g.fsf@rustcorp.com.au> User-Agent: Notmuch/0.6.1-1 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Mon, 09 Jan 2012 17:16:52 +1030 Message-ID: <877h119xur.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 6 Jan 2012 09:54:46 -0800, Mike Waychison wrote: > On Wed, Jan 4, 2012 at 6:46 PM, Mike Waychison wrote: > > On Wed, Jan 4, 2012 at 4:31 PM, Rusty Russell wrote: > >> 4) You use the skb data for the linked list; use the skb head's list. > > What did you mean by this? I was under the impression that the ->next > and ->prev fields in sk_buff were the first two elements specifically > so that the pointer could be treated as a list_head. If it's the cast > in particular that you have an objection with, I can easily change > this to a singly linked list threaded through ->next if that's > cleaner. Yep, I saw the cast and misread your code. I could have sworn that skb used a real list_head these days, but I'm wrong. > >> > >> Instead, here's how I think it should be done: > ... > > > > This sounds reasonable to me.  I'll see what I can muster together this week. > > > > So I started implementing it the way you were mentioning, and ran into > a problem with the original patchset. > > Currently the "mergeable" and "big" receive buffers use a private page > free list (virtnet_info->pages) which has no synchronization itself. > This means that the batched version can't use get_a_page() and > give_pages() as is, which reduces the need to re-use the same alloc > halves that I've split. Alternatives I can think of at this point: > > - pass in a flag to the allocators like "bool is_serial" that is true > if we are serializing with napi, (which determines if we can much with > vi->pages) > or > - not use the same allocators for the "mergeable" and "big" paths. > The mergeable allocator in the non-serialized case reduces to > alloc_page(), while the big allocator looks like a copy and paste that > uses alloc_page instead of get_a_page(). > > Preferences? I'll code one of the two up and see what it looks like. Whatever results in a cleaner driver, I'm happy. Thanks, Rusty.