Re: get_zone_device_page() in get_page() and page_cache_get_speculative()

From	"Kirill A. Shutemov" <kirill@shutemov.name>
Newsgroups	linux.kernel
Subject	Re: get_zone_device_page() in get_page() and page_cache_get_speculative()
Date	2017-04-24 20:10 +0200
Message-ID	<tzQAW-1Uk-15@gated-at.bofh.it> (permalink)
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On Mon, Apr 24, 2017 at 10:47:43AM -0700, Dan Williams wrote:
> On Mon, Apr 24, 2017 at 10:30 AM, Kirill A. Shutemov
> >> >> [   35.423841] WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155
> >> >> percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
> >> >
> >> > Okay, I've tracked it down. The issue is triggered by replacment
> >> > get_page() with page_cache_get_speculative().
> >> >
> >> > page_cache_get_speculative() doesn't have get_zone_device_page(). :-|
> >> >
> >> > And I think it's your bug, Dan: it's wrong to have
> >> > get_/put_zone_device_page() in get_/put_page(). I must be handled by
> >> > page_ref_* machinery to catch all cases where we manipulate with page
> >> > refcount.
> >>
> >> The page_ref conversion landed in 4.6 *after* the ZONE_DEVICE
> >> implementation that landed in 4.5, so there was a missed conversion of
> >> the zone-device reference counting to page_ref.
> >
> > Fair enough.
> >
> > But get_page_unless_zero() definitely predates ZONE_DEVICE. :)
> >
> 
> It does, but that's deliberate. A ZONE_DEVICE page never has a zero
> reference count, it's always owned by the device, never by the page
> allocator. ZONE_DEVICE overrides the ->lru list_head to store private
> device information and we rely on the behavior that a non-zero
> reference means the page is not added to any lru or page cache list.

So, what do you propose? Use get_page() instead of
page_cache_get_speculative() in GUP_fast() if the page belong to zone
device?

I don't like it. This situation, when we only can use subset of
helpers to manipulate page refcount creates situation waiting to explode.

I think it's still better to do it on page_ref_* level.

BTW, why do we need to pin pgmap from get_page() in first place?
I don't have enough background in ZONE_DEVICE.

-- 
 Kirill A. Shutemov

Thread

Re: [tip:x86/mm] x86/mm/gup: Switch GUP to the generic  get_user_page_fast() implementation Dan Williams <dan.j.williams@intel.com> - 2017-04-20 23:50 +0200
  Re: [tip:x86/mm] x86/mm/gup: Switch GUP to the generic  get_user_page_fast() implementation "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-21 16:20 +0200
    Re: [tip:x86/mm] x86/mm/gup: Switch GUP to the generic  get_user_page_fast() implementation Dan Williams <dan.j.williams@intel.com> - 2017-04-21 21:40 +0200
      [PATCH] Revert "x86/mm/gup: Switch GUP to the generic  get_user_page_fast() implementation" Ingo Molnar <mingo@kernel.org> - 2017-04-23 12:00 +0200
  get_zone_device_page() in get_page() and page_cache_get_speculative() "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-24 01:40 +0200
    Re: get_zone_device_page() in get_page() and page_cache_get_speculative() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 19:30 +0200
      Re: get_zone_device_page() in get_page() and  page_cache_get_speculative() "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-24 19:40 +0200
        Re: get_zone_device_page() in get_page() and page_cache_get_speculative() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 19:50 +0200
          Re: get_zone_device_page() in get_page() and  page_cache_get_speculative() "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-04-24 20:10 +0200
            Re: get_zone_device_page() in get_page() and  page_cache_get_speculative() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-04-24 20:30 +0200
              Re: get_zone_device_page() in get_page() and page_cache_get_speculative() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 20:50 +0200
                Re: get_zone_device_page() in get_page() and  page_cache_get_speculative() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-04-25 15:30 +0200
                Re: get_zone_device_page() in get_page() and page_cache_get_speculative() Dan Williams <dan.j.williams@intel.com> - 2017-04-25 18:50 +0200
    [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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