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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 2017-06-01 09:00 +0200
Message-ID <tNsfo-7wq-7@gated-at.bofh.it> (permalink)
References (5 earlier) <tMQD7-ar-3@gated-at.bofh.it> <tMRzc-KJ-11@gated-at.bofh.it> <tNaBR-4zj-35@gated-at.bofh.it> <tNb4R-4IS-5@gated-at.bofh.it> <tNcDE-5Wy-19@gated-at.bofh.it>
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On Wed, May 31, 2017 at 04:18:09PM +0200, Andrea Arcangeli wrote:
> On Wed, May 31, 2017 at 03:39:22PM +0300, Mike Rapoport wrote:
> > For the CRIU usecase, disabling THP for a while and re-enabling it
> > back will do the trick, provided VMAs flags are not affected, like
> > in the patch you've sent.  Moreover, we may even get away with
> 
> Are you going to check uname -r to know when the kABI changed in your
> favor (so CRIU cannot ever work with enterprise backports unless you
> expand the uname -r coverage), or how do you know the patch is
> applied?

CRIU does not rely on uname -r. We have code that checks what kernel
features we can actually use. For instance, we use UFFDIO_API to see if we
can do post-copy at all.
 
> Optimistically assuming people is going to run new CRIU code only on
> new kernels looks very risky, it would leads to silent random memory
> corruption, so I doubt you can get away without a uname -r check.
> 
> This is fairly simple change too, its main cons is that it adds a
> branch to the page fault fast path, the old behavior of the prctl and
> the new madvise were both zero cost.
> 
> Still if the prctl is preferred despite the added branch, to avoid
> uname -r clashes, to me it sounds better to add a new prctl ID and
> keep the old one too. The old one could be implemented the same way as
> the new one if you want to save a few bytes of .text. But the old one
> should probably do a printk_once to print a deprecation warning so the
> old ID with weaker (zero runtime cost) semantics can be removed later.
>

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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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