linux-kernel - Re: [PATCH] thp: reduce usage of huge zero page's atomic counter

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Date:   Wed, 31 Aug 2016 00:59:19 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        "'Kirill A. Shutemov'" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Jerome Marchand <jmarchan@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ebru Akagunduz <ebru.akagunduz@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thp: reduce usage of huge zero page's atomic counter

On (08/29/16 14:31), Aaron Lu wrote:
> 
> The global zero page is used to satisfy an anonymous read fault. If
> THP(Transparent HugePage) is enabled then the global huge zero page is used.
> The global huge zero page uses an atomic counter for reference counting
> and is allocated/freed dynamically according to its counter value.
> 

Hello,

for !CONFIG_TRANSPARENT_HUGEPAGE configs mm_put_huge_zero_page() is BUILD_BUG(),
which gives the following build error (mmots v4.8-rc4-mmots-2016-08-29-16-56)


  CC      kernel/fork.o
In file included from ./include/asm-generic/bug.h:4:0,
                 from ./arch/x86/include/asm/bug.h:35,
                 from ./include/linux/bug.h:4,
                 from ./include/linux/mmdebug.h:4,
                 from ./include/linux/gfp.h:4,
                 from ./include/linux/slab.h:14,
                 from kernel/fork.c:14:
In function ‘mm_put_huge_zero_page’,
    inlined from ‘__mmput’ at kernel/fork.c:777:2,
    inlined from ‘mmput_async_fn’ at kernel/fork.c:806:2:
./include/linux/compiler.h:495:38: error: call to ‘__compiletime_assert_218’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:478:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:495:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/bug.h:51:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/bug.h:85:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^~~~~~~~~~~~~~~~
./include/linux/huge_mm.h:218:2: note: in expansion of macro ‘BUILD_BUG’
  BUILD_BUG();
  ^~~~~~~~~
In function ‘mm_put_huge_zero_page’,
    inlined from ‘__mmput’ at kernel/fork.c:777:2,
    inlined from ‘mmput’ at kernel/fork.c:798:3:
./include/linux/compiler.h:495:38: error: call to ‘__compiletime_assert_218’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:478:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:495:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/bug.h:51:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/bug.h:85:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^~~~~~~~~~~~~~~~
./include/linux/huge_mm.h:218:2: note: in expansion of macro ‘BUILD_BUG’
  BUILD_BUG();
  ^~~~~~~~~
make[1]: *** [scripts/Makefile.build:291: kernel/fork.o] Error 1
make: *** [Makefile:968: kernel] Error 2


	-ss