On May 22, 2018, at 5:13 AM, Michal Hocko <[email protected]> wrote: > > [CC Kirill] > > On Mon 21-05-18 12:38:53, 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(). >> >> This patch fixes these problems by reusing hugepage_vma_check() in >> khugepaged_enter_vma_merge(). > > It would be great to be more explicit about what are the actual > consequences. khugepaged_enter_vma_merge is called from multiple > context. Some of then do not really care about !anon case (e.g. stack > expansion). hugepage_madvise is quite convoluted so I am not really sure > from a quick look (are we simply not going to merge vmas even if we > could?).
Yes, it does fix madvise for shmem with huge=advise option. I had made a mistake in this version. I will send v2 with the more details on what is fixed. > Have you noticed this by a code inspection or you have seen this > happening in real workloads (aka, is this worth backporting to stable > trees)? I noticed this when reading the code. I think this might worth back porting. However, I don't know whether it fixes anything else other than shmem, so I am not sure which versions need this fix. Thanks, Song >> Signed-off-by: Song Liu <[email protected]> >> --- >> mm/khugepaged.c | 12 ++++-------- >> 1 file changed, 4 insertions(+), 8 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index d7b2a4b..e50c2bd 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -430,18 +430,14 @@ int __khugepaged_enter(struct mm_struct *mm) >> return 0; >> } >> >> +static bool hugepage_vma_check(struct vm_area_struct *vma); >> + >> int khugepaged_enter_vma_merge(struct vm_area_struct *vma, >> unsigned long vm_flags) >> { >> unsigned long hstart, hend; >> - 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 */ >> + >> + if (!hugepage_vma_check(vma)) >> return 0; >> hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; >> hend = vma->vm_end & HPAGE_PMD_MASK; >> -- >> 2.9.5 > > -- > Michal Hocko > SUSE Labs
