Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758076Ab3CUMX7 (ORCPT ); Thu, 21 Mar 2013 08:23:59 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:40183 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757902Ab3CUMX5 (ORCPT ); Thu, 21 Mar 2013 08:23:57 -0400 Message-ID: <514AFBD4.2050201@linux.vnet.ibm.com> Date: Thu, 21 Mar 2013 08:23:48 -0400 From: "Michael R. Hines" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Roland Dreier , Sean Hefty , Hal Rosenstock , Yishai Hadas , Christoph Lameter , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [PATCH] rdma: don't make pages writeable if not requiested References: <20130321061838.GA28319@redhat.com> In-Reply-To: <20130321061838.GA28319@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13032112-5806-0000-0000-0000206CF057 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2204 Lines: 54 Yes, I'd be happy to try the patch. Got meetings all day...... but will dive in soon. On 03/21/2013 02:18 AM, Michael S. Tsirkin wrote: > core/umem.c seems to get the arguments to get_user_pages > in the reverse order: it sets writeable flag and > breaks COW for MAP_SHARED if and only if hardware needs to > write the page. > > This breaks memory overcommit for users such as KVM: > each time we try to register a page to send it to remote, this > breaks COW. It seems that for applications that only have > REMOTE_READ permission, there is no reason to break COW at all. > > If the page that is COW has lots of copies, this makes the user process > quickly exceed the cgroups memory limit. This makes RDMA mostly useless > for virtualization, thus the stable tag. > > Reported-by: "Michael R. Hines" > Cc: stable@vger.kernel.org > Signed-off-by: Michael S. Tsirkin > --- > > Note: compile-tested only, I don't have RDMA hardware at the moment. > Michael, could you please try this patch (also fixing your > usespace code not to request write access) and report? > > Note2: grep for get_user_pages in infiniband drivers turns up > lots of users who set write to 1 unconditionally. > These might be bugs too, should be checked. > > drivers/infiniband/core/umem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c > index a841123..5929598 100644 > --- a/drivers/infiniband/core/umem.c > +++ b/drivers/infiniband/core/umem.c > @@ -152,7 +152,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr, > ret = get_user_pages(current, current->mm, cur_base, > min_t(unsigned long, npages, > PAGE_SIZE / sizeof (struct page *)), > - 1, !umem->writable, page_list, vma_list); > + !umem->writable, 1, page_list, vma_list); > > if (ret < 0) > goto out; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/