linux-kernel - Re: [PATCH v9 05/10] mm: thp: enable thp migration in generic path

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Date:   Wed, 19 Jul 2017 22:54:04 -0400
From:   "Zi Yan" <zi.yan@...rutgers.edu>
To:     "Andrew Morton" <akpm@...ux-foundation.org>
Cc:     "kbuild test robot" <lkp@...el.com>, kbuild-all@...org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com, minchan@...nel.org,
        vbabka@...e.cz, mgorman@...hsingularity.net, mhocko@...nel.org,
        khandual@...ux.vnet.ibm.com, dnellans@...dia.com,
        dave.hansen@...el.com, n-horiguchi@...jp.nec.com
Subject: Re: [PATCH v9 05/10] mm: thp: enable thp migration in generic path

On 19 Jul 2017, at 16:59, Andrew Morton wrote:

> On Wed, 19 Jul 2017 14:39:43 -0400 "Zi Yan" <zi.yan@...rutgers.edu> 
> wrote:
>
>> On 19 Jul 2017, at 4:04, kbuild test robot wrote:
>>
>>> Hi Zi,
>>>
>>> [auto build test WARNING on mmotm/master]
>>> [also build test WARNING on v4.13-rc1 next-20170718]
>>> [if your patch is applied to the wrong git tree, please drop us a 
>>> note to help improve the system]
>>>
>>> url:    
>>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2F0day-ci%2Flinux%2Fcommits%2FZi-Yan%2Fmm-page-migration-enhancement-for-thp%2F20170718-095519&data=02%7C01%7Czi.yan%40cs.rutgers.edu%7Ca711ac47d4c0436ef66f08d4ce7cf30c%7Cb92d2b234d35447093ff69aca6632ffe%7C1%7C0%7C636360483431631457&sdata=NpxRpWbxe6o56xDJYpw1K6wgQo11IPCAbG2tE8l%2BU6E%3D&reserved=0
>>> base:   git://git.cmpxchg.org/linux-mmotm.git master
>>> config: xtensa-common_defconfig (attached as .config)
>>> compiler: xtensa-linux-gcc (GCC) 4.9.0
>>> reproduce:
>>>         wget 
>>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fraw.githubusercontent.com%2F01org%2Flkp-tests%2Fmaster%2Fsbin%2Fmake.cross&data=02%7C01%7Czi.yan%40cs.rutgers.edu%7Ca711ac47d4c0436ef66f08d4ce7cf30c%7Cb92d2b234d35447093ff69aca6632ffe%7C1%7C0%7C636360483431631457&sdata=rBCfu0xUg3v%2B8r%2Be2tsiqRcqw%2FEZSTa4OtF0hU%2FqMbc%3D&reserved=0 
>>> -O ~/bin/make.cross
>>>         chmod +x ~/bin/make.cross
>>>         # save the attached .config to linux build tree
>>>         make.cross ARCH=xtensa
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>>    In file included from mm/vmscan.c:55:0:
>>>    include/linux/swapops.h: In function 'swp_entry_to_pmd':
>>>>> include/linux/swapops.h:220:2: warning: missing braces around 
>>>>> initializer [-Wmissing-braces]
>>>      return (pmd_t){ 0 };
>>>      ^
>>>    include/linux/swapops.h:220:2: warning: (near initialization for 
>>> '(anonymous).pud') [-Wmissing-braces]
>>>
>>> vim +220 include/linux/swapops.h
>>>
>>>    217	
>>>    218	static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
>>>    219	{
>>>> 220		return (pmd_t){ 0 };
>>>    221	}
>>>    222	
>>
>> It is a GCC 4.9.0 bug: 
>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fbugzilla%2Fshow_bug.cgi%3Fid%3D53119&data=02%7C01%7Czi.yan%40cs.rutgers.edu%7C07c903c4f1444958942508d4cee90ca7%7Cb92d2b234d35447093ff69aca6632ffe%7C1%7C0%7C636360947714283172&sdata=84%2BXG7hglTCsTjGA8G3jyL7%2BFupkQaMkjAwzofffA5A%3D&reserved=0
>>
>> Upgrading GCC can get rid of this warning.
>
> I think there was a workaround for this, but I don't recall what it
> was.
>
> This suppressed the warning:
>
> --- a/include/linux/swapops.h~a
> +++ a/include/linux/swapops.h
> @@ -217,7 +217,7 @@ static inline swp_entry_t pmd_to_swp_ent
>
>  static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
>  {
> -	return (pmd_t){ 0 };
> +	return (pmd_t){};
>  }
>
>  static inline int is_pmd_migration_entry(pmd_t pmd)
>
> But I don't know if this is the approved workaround and I don't know
> what it will do at runtime!
>
> But we should fix this.  Expecting zillions of people to update their
> compiler version isn't nice.


How about this one?

--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -219,7 +219,7 @@ static inline swp_entry_t pmd_to_swp_entry(pmd_t 
pmd)

  static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
  {
-       return (pmd_t){ 0 };
+       return __pmd(0);
  }

  static inline int is_pmd_migration_entry(pmd_t pmd)


No warning or error was present during i386 kernel compilations
with gcc-4.9.3 or gcc-6.4.0. i386 gcc should share the same front-end
as xtensa-linux-gcc.

__pmd() should be the standard way of making pmd entries, right?


--
Best Regards
Yan Zi