From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rafal Wojtczuk Subject: Re: Assigning contiguous memory to a driver domain Date: Wed, 15 Sep 2010 11:08:42 +0200 Message-ID: <20100915090842.GB1583@email> References: <20100914092439.GA1000@email> <4C8F5E580200007800015F71@vpn.id2.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 Return-path: Content-Disposition: inline In-Reply-To: <4C8F5E580200007800015F71@vpn.id2.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Tue, Sep 14, 2010 at 10:36:56AM +0100, Jan Beulich wrote: > >>> On 14.09.10 at 11:24, Rafal Wojtczuk wrote: > > Hello, > > > > Could someone guide me in the right direction with the topic of assigning > > contiguous memory to a domain. > > > > I have an issue with a PV domain that is assigned a PCI device. Sometimes, > > the > > driver fails to load > > Sep 13 10:36:43 localhost kernel: [ 103.651858] iwlagn 0000:00:01.0: > > firmware: requesting iwlwifi-4965-2.ucode > > Sep 13 10:36:43 localhost kernel: [ 103.669105] iwlagn 0000:00:01.0: loaded > > firmware version 228.61.2.24 > > Sep 13 10:36:43 localhost kernel: [ 103.669263] iwlagn 0000:00:01.0: failed > > to allocate pci memory > > > > The reason seems to be that the domain does not have enough contiguous > > memory, in mfn terms. > > No, how (dis)contiguous the memory of a domain is doesn't matter > here. What matters is whether the domain can *make* the requested > memory contiguous, and that depends on how much contiguous > memory Xen has at the point of the allocation. Ah, so you are saying that regardless of whether a domain has some contiguous memory, the driver will call xen_create_contiguous_region when allocating memory (via dma_alloc_coherent ?). Slightly out-of-the-list-scope: is there a convention when a driver should allocate DMA-able memory ? Is it safe to assume that as soon as the driver has loaded, it will no longer need to call xen_create_contiguous_region anymore and we can use up all free Xen memory ? Particularly, would a network card driver need to "*make* the requested memory contiguous" whenever creating a skbuff [*] (and creating skbuffs is a frequent thing during network card life)? Thank you for your answer, regards, Rafal Wojtczuk [*] Admittedly, for a device with a sane MTU, skbuff should fit in a single frame, so no issue with contiguousness here, but thinking generic.