From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Ott Subject: Re: [RFC PATCH 04/12] s390/cio: introduce cio DMA pool Date: Thu, 11 Apr 2019 20:25:01 +0200 (CEST) Message-ID: References: <20190404231622.52531-1-pasic@linux.ibm.com> <20190404231622.52531-5-pasic@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190404231622.52531-5-pasic@linux.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Halil Pasic Cc: Farhan Ali , linux-s390@vger.kernel.org, Eric Farman , Claudio Imbrenda , Vasily Gorbik , kvm@vger.kernel.org, Cornelia Huck , virtualization@lists.linux-foundation.org, Martin Schwidefsky , Viktor Mihajlovski , Janosch Frank List-Id: virtualization@lists.linuxfoundation.org On Fri, 5 Apr 2019, Halil Pasic wrote: > To support protected virtualization cio will need to make sure the > memory used for communication with the hypervisor is DMA memory. > > Let us introduce a DMA pool to cio that will help us in allocating > deallocating those chunks of memory. > > We use a gen_pool backed with DMA pages to avoid each allocation > effectively wasting a page, as we typically allocate much less > than PAGE_SIZE. I don't think we should use this global DMA pool. I guess it's OK for stuff like airq (where we don't have a struct device at hand) but for CCW we should use the device we have. Yes, this way we waste some memory but all dma memory a device uses should fit in a page - so the wastage is not too much. Sebastian