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Re: [HMM 02/16] mm/put_page: move ref decrement to put_zone_device_page()

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On Thu, Mar 16, 2017 at 12:05:21PM -0400, J?r?me Glisse wrote:
> This does not affect non ZONE_DEVICE page. In order to allow
> ZONE_DEVICE page to be tracked we need to detect when refcount
> of a ZONE_DEVICE page reach 1 (not 0 as non ZONE_DEVICE page).
> 
> This patch just move put_page_testzero() from put_page() to
> put_zone_device_page() and only for ZONE_DEVICE. It does not
> add any overhead compare to existing code.
> 
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  include/linux/mm.h | 8 +++++---
>  kernel/memremap.c  | 2 ++
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5f01c88..28e8b28 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -793,11 +793,13 @@ static inline void put_page(struct page *page)
>  {
>  	page = compound_head(page);
>  
> +	if (unlikely(is_zone_device_page(page))) {
> +		put_zone_device_page(page);
> +		return;
> +	}
> +
>  	if (put_page_testzero(page))
>  		__put_page(page);
> -
> -	if (unlikely(is_zone_device_page(page)))
> -		put_zone_device_page(page);
>  }
>  
>  #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 40d4af8..c821946 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -190,6 +190,8 @@ EXPORT_SYMBOL(get_zone_device_page);
>  
>  void put_zone_device_page(struct page *page)
>  {
> +	page_ref_dec(page);
> +
>  	put_dev_pagemap(page->pgmap);
>  }
>  EXPORT_SYMBOL(put_zone_device_page);

So the page refcount goes to zero but where did the __put_page call go? I
haven't read the full series yet but I do note the next patch introduces
a callback. Maybe callbacks free the page but it looks optional. Maybe
it gets fixed later in the series but the changelog should at least say
this is not bisect safe and as this looks like a memory leak.

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[HMM 00/16] HMM (Heterogeneous Memory Management) v18 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
  [HMM 14/16] mm/migrate: allow migrate_vma() to alloc new page on empty entry Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
  [HMM 10/16] mm/hmm/mirror: mirror process address space on device with HMM helpers Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 10/16] mm/hmm/mirror: mirror process address space on  device with HMM helpers Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 15/16] mm/hmm/devmem: device memory hotplug using ZONE_DEVICE Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
  [HMM 09/16] mm/hmm: heterogeneous memory management (HMM for short) Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 09/16] mm/hmm: heterogeneous memory management (HMM for  short) Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 11/16] mm/hmm/mirror: helper to snapshot CPU page table v2 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 11/16] mm/hmm/mirror: helper to snapshot CPU page table v2 Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:20 +0100
  [HMM 03/16] mm/ZONE_DEVICE/free-page: callback when page is freed v3 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 03/16] mm/ZONE_DEVICE/free-page: callback when page is  freed v3 Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 04/16] mm/ZONE_DEVICE/unaddressable: add support for un-addressable device memory v3 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 04/16] mm/ZONE_DEVICE/unaddressable: add support for  un-addressable device memory v3 Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 16/16] mm/hmm/devmem: dummy HMM device for ZONE_DEVICE memory v2 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 16/16] mm/hmm/devmem: dummy HMM device for ZONE_DEVICE  memory v2 Bob Liu <liubo95@huawei.com> - 2017-03-17 08:10 +0100
      Re: [HMM 16/16] mm/hmm/devmem: dummy HMM device for ZONE_DEVICE  memory v2 Jerome Glisse <jglisse@redhat.com> - 2017-03-17 18:00 +0100
  [HMM 01/16] mm/memory/hotplug: convert device bool to int to allow for more flags v3 Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
    Re: [HMM 01/16] mm/memory/hotplug: convert device bool to int to  allow for more flags v3 Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 08/16] mm/migrate: migrate_vma() unmap page from vma while collecting pages Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
  [HMM 13/16] mm/hmm/migrate: support un-addressable ZONE_DEVICE page in migration Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:20 +0100
  [HMM 05/16] mm/ZONE_DEVICE/x86: add support for un-addressable device memory Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:30 +0100
  [HMM 02/16] mm/put_page: move ref decrement to put_zone_device_page() Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:30 +0100
    Re: [HMM 02/16] mm/put_page: move ref decrement to  put_zone_device_page() Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  [HMM 06/16] mm/migrate: add new boolean copy flag to migratepage() callback Jérôme Glisse <jglisse@redhat.com> - 2017-03-16 16:30 +0100
    Re: [HMM 06/16] mm/migrate: add new boolean copy flag to  migratepage() callback Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:10 +0100
  Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Andrew Morton <akpm@linux-foundation.org> - 2017-03-16 21:50 +0100
    Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Jerome Glisse <jglisse@redhat.com> - 2017-03-17 01:00 +0100
      Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Bob Liu <liubo95@huawei.com> - 2017-03-17 09:30 +0100
        Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Jerome Glisse <jglisse@redhat.com> - 2017-03-17 17:00 +0100
      Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Bob Liu <liubo95@huawei.com> - 2017-03-17 09:50 +0100
        Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Jerome Glisse <jglisse@redhat.com> - 2017-03-17 17:20 +0100
  Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Mel Gorman <mgorman@techsingularity.net> - 2017-03-19 21:40 +0100

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