On Thu, Jan 28, 2016 at 1:33 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > On Wed, Jan 27, 2016 at 12:32:16PM -0800, Andy Lutomirski wrote: >> On Wed, Jan 27, 2016 at 11:39 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: >> > Could the VDSO be a VM_MIXEDMAP to keep the initial unmanaged pages >> > out of the VM while allowing COW into regular anonymous pages? >> >> Probably. What are its limitations? We want ptrace to work on it, >> and mprotect needs to work and allow COW. access_process_vm should >> probably work, too. > > Thanks, that's good to know. > > However, after looking at this a little longer, it appears this would > need work in do_wp_page() to support non-page COW copying, then adding > vm_ops->access and complicating ->fault in all VDSO implementations. > > And it looks like - at least theoretically - drivers can inject non-VM > pages into the page tables as well (comment above insert_page()) > > Given that this behavior has been around for a long time (the comment > at the bottom of vm_normal_page is ancient), I'll probably go with a > more conservative approach; add a comment to mark_page_accessed() and > filter out non-VM pages in the function I'm going to call from it. I just checked: in -tip, I'm creating a VM_PFNMAP (not VM_MIXEDMAP) vma and faulting a RAM page (with struct page and all) in using vm_insert_pfn. Is that okay, or so I need to use VM_MIXEDMAP instead? --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>