On Thu, Mar 21, 2013 at 08:23:48AM -0400, Michael R. Hines wrote: > Yes, I'd be happy to try the patch. > > Got meetings all day...... but will dive in soon.
The patch is unlikely to be the final version. In particular you need to change !umem->writable to umem->writable. > 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" <mrhi...@linux.vnet.ibm.com> > >Cc: sta...@vger.kernel.org > >Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > >--- > > > >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;
