From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael R. Hines" Subject: Re: [PATCH] rdma: don't make pages writeable if not requiested Date: Thu, 21 Mar 2013 08:23:48 -0400 Message-ID: <514AFBD4.2050201@linux.vnet.ibm.com> References: <20130321061838.GA28319@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130321061838.GA28319-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Michael S. Tsirkin" Cc: Roland Dreier , Sean Hefty , Hal Rosenstock , Yishai Hadas , Christoph Lameter , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org List-Id: linux-rdma@vger.kernel.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.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-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html