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Re: [PATCH -v3 05/10] mm, THP, swap: Add get_huge_swap_page()

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"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Wed, Sep 07, 2016 at 09:46:04AM -0700, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>> 
>> A variation of get_swap_page(), get_huge_swap_page(), is added to
>> allocate a swap cluster (512 swap slots) based on the swap cluster
>> allocation function.  A fair simple algorithm is used, that is, only the
>> first swap device in priority list will be tried to allocate the swap
>> cluster.  The function will fail if the trying is not successful, and
>> the caller will fallback to allocate a single swap slot instead.  This
>> works good enough for normal cases.
>
> For normal cases, yes. But the limitation is not obvious for users and
> performance difference after small change in configuration could be
> puzzling.

If the difference of the number of the free swap clusters among
multiple swap devices is significant, it is possible that some THP are
split earlier than necessary because we fail to allocate the swap
clusters for them.  For example, this could be caused by big size
difference among multiple swap devices.

> At least this must be documented somewhere.

I can add the above description in the patch description.  Any other
places do you suggest?

Best Regards,
Huang, Ying

[snip]

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[PATCH -v3 00/10] THP swap: Delay splitting THP during swapping out "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
  [PATCH -v3 02/10] mm, memcg: Add swap_cgroup_iter iterator "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
  [PATCH -v3 08/10] mm, THP: Add can_split_huge_page() "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 08/10] mm, THP: Add can_split_huge_page() "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-09-08 13:20 +0200
      Re: [PATCH -v3 08/10] mm, THP: Add can_split_huge_page() "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 19:10 +0200
  [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP  size on x86_64 Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 10:30 +0200
    Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP  size on x86_64 Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 11:20 +0200
      Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 20:10 +0200
    Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP  size on x86_64 "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-09-08 13:10 +0200
      Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 19:40 +0200
    Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP  size on x86_64 "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-09-08 13:10 +0200
      Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 19:30 +0200
  [PATCH -v3 05/10] mm, THP, swap: Add get_huge_swap_page() "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 05/10] mm, THP, swap: Add get_huge_swap_page() "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-09-08 13:20 +0200
      Re: [PATCH -v3 05/10] mm, THP, swap: Add get_huge_swap_page() "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 19:30 +0200
  [PATCH -v3 09/10] mm, THP, swap: Support to split THP in swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
  [PATCH -v3 06/10] mm, THP, swap: Support to clear SWAP_HAS_CACHE for huge page "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
  [PATCH -v3 03/10] mm, memcg: Support to charge/uncharge multiple swap entries "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 03/10] mm, memcg: Support to charge/uncharge multiple  swap entries Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 10:30 +0200
      Re: [PATCH -v3 03/10] mm, memcg: Support to charge/uncharge multiple swap entries "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 20:20 +0200
    Re: [PATCH -v3 03/10] mm, memcg: Support to charge/uncharge multiple  swap entries Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 10:40 +0200
  [PATCH -v3 04/10] mm, THP, swap: Add swap cluster allocate/free functions "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 04/10] mm, THP, swap: Add swap cluster allocate/free  functions Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 10:40 +0200
      Re: [PATCH -v3 04/10] mm, THP, swap: Add swap cluster allocate/free functions "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 20:20 +0200
    Re: [PATCH -v3 04/10] mm, THP, swap: Add swap cluster allocate/free  functions Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 11:00 +0200
  [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-09-07 18:50 +0200
    Re: [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from  swap cache Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-09-08 11:10 +0200
      Re: [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-09-08 20:20 +0200
  Re: [PATCH -v3 00/10] THP swap: Delay splitting THP during swapping  out Minchan Kim <minchan@kernel.org> - 2016-09-09 07:50 +0200

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