Messages in this thread | | | Date | Thu, 21 Mar 2013 09:03:57 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH] rdma: don't make pages writeable if not requiested |
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On Wed, Mar 20, 2013 at 11:55:54PM -0700, Roland Dreier wrote: > On Wed, Mar 20, 2013 at 11:18 PM, Michael S. Tsirkin <mst@redhat.com> 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. > > I proposed a similar (but not exactly the same, see below) patch a > while ago: https://lkml.org/lkml/2012/1/26/7 but read the thread, > especially https://lkml.org/lkml/2012/2/6/265 > > I think this change will break the case where userspace tries to > register an MR with read-only permission, but intends locally through > the CPU to write to the memory.
Shouldn't it set LOCAL_WRITE then?
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