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Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support
From: |
Andrea Arcangeli |
Subject: |
Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support |
Date: |
Mon, 13 Feb 2017 18:57:22 +0100 |
User-agent: |
Mutt/1.7.2 (2016-11-26) |
Hello,
On Mon, Feb 13, 2017 at 08:11:06PM +0300, Alexey Perevalov wrote:
> Another one request.
> QEMU could use mem_path in hugefs with share key simultaneously
> (-object
> memory-backend-file,id=mem,size=${mem_size},mem-path=${mem_path},share=on)
> and vm
> in this case will start and will properly work (it will allocate memory
> with mmap), but in case of destination for postcopy live migration
> UFFDIO_COPY ioctl will fail for
> such region, in Arcangeli's git tree there is such prevent check
> (if (!vma_is_shmem(dst_vma) && dst_vma->vm_flags & VM_SHARED).
> Is it possible to handle such situation at qemu?
It'd be nice to lift this hugetlbfs !VM_SHARED restriction I agree, I
already asked Mike (CC'ed) why is there, because I'm afraid it's a
leftover from the anon version where VM_SHARED means a very different
thing but it was already lifted for shmem. share=on should already
work on top of tmpfs and also with THP on tmpfs enabled.
For hugetlbfs and shmem it should be generally more complicated to
cope with private mappings than shared ones, shared is just the native
form of the pseudofs without having to deal with private COWs aliases
so it's hard to imagine something going wrong for VM_SHARED if the
MAP_PRIVATE mapping already works fine. If it turns out to be
superflous the check may be just turned into
"vma_is_anonymous(dst_vma) && dst_vma->vm_flags & VM_SHARED".
Thanks,
Andrea
- [Qemu-devel] [PATCH v2 11/16] postcopy: Mask fault addresses to huge page boundary, (continued)
- [Qemu-devel] [PATCH v2 11/16] postcopy: Mask fault addresses to huge page boundary, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 08/16] postcopy: Plumb pagesize down into place helpers, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 13/16] postcopy: Allow hugepages, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 14/16] postcopy: Update userfaultfd.h header, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 12/16] postcopy: Send whole huge pages, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 16/16] postcopy: Add doc about hugepages and postcopy, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 10/16] postcopy: Load huge pages in one go, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 15/16] postcopy: Check for userfault+hugepage feature, Dr. David Alan Gilbert (git), 2017/02/06
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Dr. David Alan Gilbert, 2017/02/06
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Dr. David Alan Gilbert, 2017/02/13
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Alexey Perevalov, 2017/02/14
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Dr. David Alan Gilbert, 2017/02/14
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Alexey Perevalov, 2017/02/21
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Dr. David Alan Gilbert, 2017/02/21