From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [Xen-devel] [PATCH net-next 1/3] xen-netback: page pool support Date: Fri, 24 May 2013 14:34:32 +0100 Message-ID: <20130524133432.GD16745@zion.uk.xensource.com> References: <1369391553-16835-1-git-send-email-wei.liu2@citrix.com> <1369391553-16835-2-git-send-email-wei.liu2@citrix.com> <519F60AF.5020705@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Wei Liu , , , , To: David Vrabel Return-path: Received: from smtp.citrix.com ([66.165.176.89]:50840 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751114Ab3EXNee (ORCPT ); Fri, 24 May 2013 09:34:34 -0400 Content-Disposition: inline In-Reply-To: <519F60AF.5020705@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, May 24, 2013 at 01:44:31PM +0100, David Vrabel wrote: > On 24/05/13 11:32, Wei Liu wrote: > > This patch implements a page pool for all vifs. It has two functionalities: > > a) to limit the amount of pages used by all vifs > > b) to track pages belong to vifs > > This adds a global spin lock. This doesn't seem very scalable. > > It's also not clear how this is usefully limiting the memory usage by > guest network traffic. It limits the number of pages that netback can > use during the grant copy from the guest pages but this is only short > time compared to the lifetime of the network packet within the rest of > the network stack. > > If you didn't have this page pool stuff then each thread/VIF is limited > to at most 256 pages anyway and I think 1 MiB of memory per VIF is > perfectly acceptable. > Oh I forgot to mention another important function of page pool -- to track pages. With this tracking facility it is really tricky to make thread-per-vif work. If you look at the original code, you can see we steal page->mapping field for tracking purpose. The netback ref is stored in that field. When switching to 1:1 model, the information embedded into page->mapping is the index to pool element. If we don't have this pool, tracking becomes more difficult. Wei. > David