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Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT |
Date: |
Tue, 7 Oct 2014 11:46:04 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* Kirill A. Shutemov (address@hidden) wrote:
> On Fri, Oct 03, 2014 at 07:07:58PM +0200, Andrea Arcangeli wrote:
> > MADV_USERFAULT is a new madvise flag that will set VM_USERFAULT in the
> > vma flags. Whenever VM_USERFAULT is set in an anonymous vma, if
> > userland touches a still unmapped virtual address, a sigbus signal is
> > sent instead of allocating a new page. The sigbus signal handler will
> > then resolve the page fault in userland by calling the
> > remap_anon_pages syscall.
>
> Hm. I wounder if this functionality really fits madvise(2) interface: as
> far as I understand it, it provides a way to give a *hint* to kernel which
> may or may not trigger an action from kernel side. I don't think an
> application will behaive reasonably if kernel ignore the *advise* and will
> not send SIGBUS, but allocate memory.
Aren't DONTNEED and DONTDUMP similar cases of madvise operations that are
expected to do what they say ?
> I would suggest to consider to use some other interface for the
> functionality: a new syscall or, perhaps, mprotect().
Dave
> --
> Kirill A. Shutemov
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages, (continued)
- [Qemu-devel] [PATCH 02/17] mm: gup: add get_user_pages_locked and get_user_pages_unlocked, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 05/17] mm: gup: use get_user_pages_fast and get_user_pages_unlocked, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 12/17] mm: sys_remap_anon_pages, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 17/17] userfaultfd: implement USERFAULTFD_RANGE_REGISTER|UNREGISTER, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT, Andrea Arcangeli, 2014/10/03
- Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT, Andrea Arcangeli, 2014/10/07
- Re: [Qemu-devel] [PATCH 08/17] mm: madvise MADV_USERFAULT, Kirill A. Shutemov, 2014/10/07
Re: [Qemu-devel] [PATCH 00/17] RFC: userfault v2, zhanghailiang, 2014/10/27