Re: [PATCH 0/8] add mTHP support for anonymous shmem

[Baolin Wang]

Hi Lance,

On 2024/5/6 18:54, Lance Yang wrote:
> Hey Baolin,
>
> I found a compilation issue that failed one[1] of my configurations
> after applying this series. The error message is as follows:
>
> mm/shmem.c: In function ‘shmem_get_unmapped_area’:
> ././include/linux/compiler_types.h:460:45: error: call to ‘__compiletime_assert_481’ declared with attribute error: BUILD_BUG failed
>          _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>                                              ^
> ././include/linux/compiler_types.h:441:25: note: in definition of macro ‘__compiletime_assert’
>                           prefix ## suffix();                             \
>                           ^~~~~~
> ././include/linux/compiler_types.h:460:9: note: in expansion of macro ‘_compiletime_assert’
>          _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>          ^~~~~~~~~~~~~~~~~~~
> ./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
>   #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                       ^~~~~~~~~~~~~~~~~~
> ./include/linux/build_bug.h:59:21: 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:97:28: note: in expansion of macro ‘BUILD_BUG’
>   #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
>                              ^~~~~~~~~
> ./include/linux/huge_mm.h:104:35: note: in expansion of macro ‘HPAGE_PMD_SHIFT’
>   #define HPAGE_PMD_SIZE  ((1UL) << HPAGE_PMD_SHIFT)
>                                     ^~~~~~~~~~~~~~~
> mm/shmem.c:2419:36: note: in expansion of macro ‘HPAGE_PMD_SIZE’
>          unsigned long hpage_size = HPAGE_PMD_SIZE;
>                                     ^~~~~~~~~~~~~~~
>
> It seems like we need to handle the case where CONFIG_PGTABLE_HAS_HUGE_LEAVES
> is undefined.
>
> [1] export ARCH=arm64 && make allnoconfig && make olddefconfig && make -j$(nproc)

Thanks for reporting. I can move the use of HPAGE_PMD_SIZE to after the 
check for CONFIG_TRANSPARENT_HUGEPAGE, which can avoid the building error:

diff --git a/mm/shmem.c b/mm/shmem.c
index 1af2f0aa384d..d603e36e0f4f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2416,7 +2416,7 @@ unsigned long shmem_get_unmapped_area(struct file 
*file,
        unsigned long inflated_len;
        unsigned long inflated_addr;
        unsigned long inflated_offset;
-       unsigned long hpage_size = HPAGE_PMD_SIZE;
+       unsigned long hpage_size;

        if (len > TASK_SIZE)
                return -ENOMEM;
@@ -2446,6 +2446,7 @@ unsigned long shmem_get_unmapped_area(struct file 
*file,
        if (uaddr == addr)
                return addr;

+       hpage_size = HPAGE_PMD_SIZE;
        if (shmem_huge != SHMEM_HUGE_FORCE) {
                struct super_block *sb;
                unsigned long __maybe_unused hpage_orders;