Re: [PATCH v3 4/6] mm: pvmw: add support for walking devmap pages

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 28 Feb 2022 14:35:34 +0800 Muchun Song <songmuchun@bytedance.com> wrote:

> The devmap pages can not use page_vma_mapped_walk() to check if a huge
> devmap page is mapped into a vma.  Add support for walking huge devmap
> pages so that DAX can use it in the next patch.
> 

x86_64 allnoconfig:

In file included from <command-line>:
In function 'check_pmd',
    inlined from 'page_vma_mapped_walk' at mm/page_vma_mapped.c:219:10:
././include/linux/compiler_types.h:347:45: error: call to '__compiletime_assert_232' declared with attribute error: BUILD_BUG failed
  347 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                             ^
././include/linux/compiler_types.h:328:25: note: in definition of macro '__compiletime_assert'
  328 |                         prefix ## suffix();                             \
      |                         ^~~~~~
././include/linux/compiler_types.h:347:9: note: in expansion of macro '_compiletime_assert'
  347 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
   39 | #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'
   59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
      |                     ^~~~~~~~~~~~~~~~
./include/linux/huge_mm.h:307:28: note: in expansion of macro 'BUILD_BUG'
  307 | #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
      |                            ^~~~~~~~~
./include/linux/huge_mm.h:104:26: note: in expansion of macro 'HPAGE_PMD_SHIFT'
  104 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
      |                          ^~~~~~~~~~~~~~~
./include/linux/huge_mm.h:105:26: note: in expansion of macro 'HPAGE_PMD_ORDER'
  105 | #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
      |                          ^~~~~~~~~~~~~~~
mm/page_vma_mapped.c:113:20: note: in expansion of macro 'HPAGE_PMD_NR'
  113 |         if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
      |                    ^~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:288: mm/page_vma_mapped.o] Error 1
make: *** [Makefile:1971: mm] Error 2


because check_pmd() uses HPAGE_PMD_NR and

#else /* CONFIG_TRANSPARENT_HUGEPAGE */
#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })

I don't immediately see why this patch triggers it...