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

[Sergey Senozhatsky]

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 âmm_put_huge_zero_pageâ,
    inlined from â__mmputâ at kernel/fork.c:777:2,
    inlined from âmmput_async_fnâ at kernel/fork.c:806:2:
./include/linux/compiler.h:495:38: error: call to â__compiletime_assert_218â 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 â__compiletime_assertâ
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:495:2: note: in expansion of macro â_compiletime_assertâ
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/bug.h:51:37: note: in expansion of macro âcompiletime_assertâ
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/bug.h:85:21: note: in expansion of macro âBUILD_BUG_ON_MSGâ
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^~~~~~~~~~~~~~~~
./include/linux/huge_mm.h:218:2: note: in expansion of macro âBUILD_BUGâ
  BUILD_BUG();
  ^~~~~~~~~
In function âmm_put_huge_zero_pageâ,
    inlined from â__mmputâ at kernel/fork.c:777:2,
    inlined from âmmputâ at kernel/fork.c:798:3:
./include/linux/compiler.h:495:38: error: call to â__compiletime_assert_218â 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 â__compiletime_assertâ
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:495:2: note: in expansion of macro â_compiletime_assertâ
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/bug.h:51:37: note: in expansion of macro âcompiletime_assertâ
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/bug.h:85:21: note: in expansion of macro âBUILD_BUG_ON_MSGâ
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^~~~~~~~~~~~~~~~
./include/linux/huge_mm.h:218:2: note: in expansion of macro âBUILD_BUGâ
  BUILD_BUG();
  ^~~~~~~~~
make[1]: *** [scripts/Makefile.build:291: kernel/fork.o] Error 1
make: *** [Makefile:968: kernel] Error 2


	-ss