On Tue, May 22, 2018 at 12:44:30PM -0700, Song Liu wrote: > khugepaged_enter_vma_merge() is using a different approach to check > whether a vma is valid for khugepaged_enter(): > > if (!vma->anon_vma) > /* > * Not yet faulted in so we will register later in the > * page fault if needed. > */ > return 0; > if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED)) > /* khugepaged not yet working on file or special mappings */ > return 0; > > This check has some problems. One of the obvious problems is that > it doesn't check shmem_file(), so that vma backed with shmem files > will not call khugepaged_enter(). Here is an example of failed madvise(): > > /* mount /dev/shm with huge=advise: > * mount -o remount,huge=advise /dev/shm */ > /* create file /dev/shm/huge */ > #define HUGE_FILE "/dev/shm/huge" > > fd = open(HUGE_FILE, O_RDONLY); > ptr = mmap(NULL, FILE_SIZE, PROT_READ, MAP_PRIVATE, fd, 0); > ret = madvise(ptr, FILE_SIZE, MADV_HUGEPAGE); > > madvise() will return 0, but this memory region is never put in huge > page (check from /proc/meminfo: ShmemHugePages). > > This patch fixes these problems by reusing hugepage_vma_check() in > khugepaged_enter_vma_merge(). > > vma->vm_flags is not yet updated in khugepaged_enter_vma_merge(), > so we need to pass the new vm_flags to hugepage_vma_check() through > a separate argument. > > Signed-off-by: Song Liu <songliubraving@xxxxxx> > --- > mm/khugepaged.c | 26 ++++++++++++-------------- > 1 file changed, 12 insertions(+), 14 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index d7b2a4b..9f74e51 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -430,18 +430,15 @@ int __khugepaged_enter(struct mm_struct *mm) > return 0; > } > > +static bool hugepage_vma_check(struct vm_area_struct *vma, > + unsigned long vm_flags); > + The patch looks good to me. But can we move hugepage_vma_check() here to avoid forward declaration of the function? -- Kirill A. Shutemov
