> On May 28, 2018, at 3:57 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > 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? Thanks for the feedback! I will send v3 with this change. Song
