From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx141.postini.com [74.125.245.141]) by kanga.kvack.org (Postfix) with SMTP id DDDFA6B0031 for ; Tue, 4 Jun 2013 11:48:32 -0400 (EDT) Received: by mail-qa0-f47.google.com with SMTP id hv16so316007qab.20 for ; Tue, 04 Jun 2013 08:48:32 -0700 (PDT) Date: Tue, 4 Jun 2013 11:45:01 -0400 From: Jerome Glisse Subject: Re: Handling NUMA page migration Message-ID: <20130604154500.GA5664@gmail.com> References: <201306040922.10235.frank.mehnert@oracle.com> <20130604115807.GF3672@sgi.com> <201306041414.52237.frank.mehnert@oracle.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="KsGdsel6WgEHnImy" Content-Disposition: inline In-Reply-To: <201306041414.52237.frank.mehnert@oracle.com> Sender: owner-linux-mm@kvack.org List-ID: To: Frank Mehnert Cc: Robin Holt , linux-mm@kvack.org, "linux-kernel@vger.kernel.org" , Hugh Dickins --KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Jun 04, 2013 at 02:14:45PM +0200, Frank Mehnert wrote: > On Tuesday 04 June 2013 13:58:07 Robin Holt wrote: > > This is probably more appropriate to be directed at the linux-mm > > mailing list. > > > > On Tue, Jun 04, 2013 at 09:22:10AM +0200, Frank Mehnert wrote: > > > Hi, > > > > > > our memory management on Linux hosts conflicts with NUMA page migration. > > > I assume this problem existed for a longer time but Linux 3.8 introduced > > > automatic NUMA page balancing which makes the problem visible on > > > multi-node hosts leading to kernel oopses. > > > > > > NUMA page migration means that the physical address of a page changes. > > > This is fatal if the application assumes that this never happens for > > > that page as it was supposed to be pinned. > > > > > > We have two kind of pinned memory: > > > > > > A) 1. allocate memory in userland with mmap() > > > > > > 2. madvise(MADV_DONTFORK) > > > 3. pin with get_user_pages(). > > > 4. flush dcache_page() > > > 5. vm_flags |= (VM_DONTCOPY | VM_LOCKED) > > > > > > (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND | > > > > > > VM_DONTCOPY | VM_LOCKED | 0xff) > > > > I don't think this type of allocation should be affected. The > > get_user_pages() call should elevate the pages reference count which > > should prevent migration from completing. I would, however, wait for > > a more definitive answer. > > Thanks Robin! Actually case B) is more important for us so I'm waiting > for more feedback :) > > Frank > > > > B) 1. allocate memory with alloc_pages() > > > > > > 2. SetPageReserved() > > > 3. vm_mmap() to allocate a userspace mapping > > > 4. vm_insert_page() > > > 5. vm_flags |= (VM_DONTEXPAND | VM_DONTDUMP) > > > > > > (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND | > > > 0xff) > > > > > > At least the memory allocated like B) is affected by automatic NUMA page > > > migration. I'm not sure about A). > > > > > > 1. How can I prevent automatic NUMA page migration on this memory? > > > 2. Can NUMA page migration also be handled on such kind of memory without > > > > > > preventing migration? > > > > > > Thanks, > > > > > > Frank I was looking at migration code lately, and while i am not an expert at all in this area. I think there is a bug in the way handle_mm_fault deals, or rather not deals, with migration entry. When huge page is migrated its pmd is replace with a special swp entry pmd, which is a non zero pmd but that does not have any of the huge pmd flag set so none of the handle_mm_fault path detect it as swap entry. Then believe its a valid pmd and try to allocate pte under it which should oops. Attached patch is what i believe should be done (not even compile tested). Again i might be missing a subtelty somewhere else and just missed where huge migration entry are dealt with. Cheers, Jerome --KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0001-mm-properly-handle-fault-on-huge-page-migration.patch" --KsGdsel6WgEHnImy--