Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference
Date	2017-04-28 21:30 +0200
Message-ID	<tBjKy-3t4-19@gated-at.bofh.it> (permalink)
References	(2 earlier) <tBi26-2bq-17@gated-at.bofh.it> <tBibL-2h5-11@gated-at.bofh.it> <tBiv7-2EY-5@gated-at.bofh.it> <tBjrb-3jU-5@gated-at.bofh.it> <tBjAR-3oJ-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Apr 28, 2017 at 12:16 PM, Jerome Glisse <jglisse@redhat.com> wrote:
>> On Fri, Apr 28, 2017 at 11:00 AM, Jerome Glisse <jglisse@redhat.com> wrote:
>> >> On Fri, Apr 28, 2017 at 10:34 AM, Jerome Glisse <jglisse@redhat.com>
>> >> wrote:
>> >> >> Kirill points out that the calls to {get,put}_dev_pagemap() can be
>> >> >> removed from the mm fast path if we take a single get_dev_pagemap()
>> >> >> reference to signify that the page is alive and use the final put of
>> >> >> the
>> >> >> page to drop that reference.
>> >> >>
>> >> >> This does require some care to make sure that any waits for the
>> >> >> percpu_ref to drop to zero occur *after* devm_memremap_page_release(),
>> >> >> since it now maintains its own elevated reference.
>> >> >
>> >> > This is NAK from HMM point of view as i need those call. So if you
>> >> > remove
>> >> > them now i will need to add them back as part of HMM.
>> >>
>> >> I thought you only need them at page free time? You can still hook
>> >> __put_page().
>> >
>> > No, i need a hook when page refcount reach 1, not 0. That being said
>> > i don't care about put_dev_pagemap(page->pgmap); so that part of the
>> > patch is fine from HMM point of view but i definitly need to hook my-
>> > self in the general put_page() function.
>> >
>> > So i will have to undo part of this patch for HMM (put_page() will
>> > need to handle ZONE_DEVICE page differently).
>>
>> Ok, I'd rather this go in now since it fixes the existing use case,
>> and unblocks the get_user_pages_fast() conversion to generic code.
>> That also gives Kirill and -mm folks a chance to review what HMM wants
>> to do on top of the page_ref infrastructure.  The
>> {get,put}_zone_device_page interface went in in 4.5 right before
>> page_ref went in during 4.6, so it was just an oversight that
>> {get,put}_zone_device_page were not removed earlier.
>>
>
> I don't mind this going in, i am hopping people won't ignore HMM patchset
> once i repost after 4.12 merge window. Note that there is absolutely no way
> around me hooking up inside put_page(). The only other way to do it would
> be to modify virtualy all places that call that function to handle ZONE_DEVICE
> case.

Are you sure about needing to hook the 2 -> 1 transition? Could we
change ZONE_DEVICE pages to not have an elevated reference count when
they are created so you can keep the HMM references out of the mm hot
path?

Thread

[PATCH] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-27 03:10 +0200
  Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-27 10:40 +0200
    Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Ingo Molnar <mingo@kernel.org> - 2017-04-28 08:40 +0200
      [PATCH] mm, zone_device: Replace {get, put}_zone_device_page() with a single reference "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-04-28 10:20 +0200
      [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-28 19:30 +0200
        Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-04-28 19:40 +0200
          Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-28 19:50 +0200
            Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-04-28 20:10 +0200
              Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-28 21:10 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-04-28 21:20 +0200
                Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-28 21:30 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-04-28 21:40 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-29 12:20 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-05-01 01:20 +0200
                Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-05-01 03:50 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-05-01 04:00 +0200
                Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-05-01 04:50 +0200
                Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Logan Gunthorpe <logang@deltatee.com> - 2017-05-01 05:50 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-01 12:50 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-05-01 16:00 +0200
                Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-05-01 22:30 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-05-01 22:40 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-02 13:50 +0200
                Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Jerome Glisse <jglisse@redhat.com> - 2017-05-02 15:30 +0200
        Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Ingo Molnar <mingo@kernel.org> - 2017-04-29 16:20 +0200
          Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-05-01 04:50 +0200
            Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference Ingo Molnar <mingo@kernel.org> - 2017-05-01 09:20 +0200
              Re: [PATCH v2] mm, zone_device: replace {get,  put}_zone_device_page() with a single reference "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-01 11:40 +0200
        [tip:x86/mm] mm, zone_device: Replace {get, put}_zone_device_page()  with a single reference to fix pmem crash tip-bot for Dan Williams <tipbot@zytor.com> - 2017-05-01 10:40 +0200
  Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-27 18:20 +0200
    Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Logan Gunthorpe <logang@deltatee.com> - 2017-04-27 18:40 +0200
      Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-27 18:40 +0200
        Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Dan Williams <dan.j.williams@intel.com> - 2017-04-27 18:50 +0200
        Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Logan Gunthorpe <logang@deltatee.com> - 2017-04-27 18:50 +0200
  Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page()  with a single reference Logan Gunthorpe <logang@deltatee.com> - 2017-04-27 18:20 +0200

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