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Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE

From Mike Rapoport <rppt@linux.vnet.ibm.com>
Newsgroups linux.kernel
Subject Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE
Date 2017-05-30 12:20 +0200
Message-ID <tMMpQ-63R-19@gated-at.bofh.it> (permalink)
References (5 earlier) <tKzwK-88W-17@gated-at.bofh.it> <tKC1A-1db-15@gated-at.bofh.it> <tKCuC-1DS-11@gated-at.bofh.it> <tKFsu-3ss-15@gated-at.bofh.it> <tMK4G-4lV-7@gated-at.bofh.it>
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On Tue, May 30, 2017 at 09:44:08AM +0200, Michal Hocko wrote:
> On Wed 24-05-17 17:27:36, Mike Rapoport wrote:
> > On Wed, May 24, 2017 at 01:18:00PM +0200, Michal Hocko wrote:
> [...]
> > > Why cannot khugepaged simply skip over all VMAs which have userfault
> > > regions registered? This would sound like a less error prone approach to
> > > me.
> > 
> > khugepaged does skip over VMAs which have userfault. We could register the
> > regions with userfault before populating them to avoid collapses in the
> > transition period.
> 
> Why cannot you register only post-copy regions and "manually" copy the
> pre-copy parts?

We can register only post-copy regions, but this will cause VMA
fragmentation. Now we register the entire VMA with userfaultfd, no matter
how many pages were dirtied there since the pre-dump. If we register only
post-copy regions, we will split out the VMAs for those regions.
 
> > But then we'll have to populate these regions with
> > UFFDIO_COPY which adds quite an overhead.
> 
> How big is the performance impact?

I don't have the numbers handy, but for each post-copy range it means that
instead of memcpy() we will use ioctl(UFFDIO_COPY).

> -- 
> Michal Hocko
> SUSE Labs
 
--
Sincerely yours,
Mike.

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Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 09:50 +0200
  Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-30 12:20 +0200
    Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 12:50 +0200
      Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 16:10 +0200
        Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 16:50 +0200
          Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 17:00 +0200
            Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 18:10 +0200
              Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-31 08:40 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 10:30 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-31 11:30 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 12:30 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 12:30 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 13:10 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-06-01 14:30 +0200
          Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 17:50 +0200
            Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 14:10 +0200
              Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoprt <rppt@linux.vnet.ibm.com> - 2017-05-31 14:40 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-31 16:20 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 16:40 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-31 17:50 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 09:00 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 16:20 +0200
          Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 09:00 +0200
            Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-06-01 10:10 +0200
              Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 10:40 +0200
              Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-06-01 15:50 +0200
                Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-02 11:20 +0200
      Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-31 11:10 +0200
        Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 14:10 +0200
          Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoprt <rppt@linux.vnet.ibm.com> - 2017-05-31 14:30 +0200

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