| Message ID | 20180521193853.3089484-1-songliubraving@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 2018-05-21 at 12:38 -0700, Song Liu wrote: > This patch fixes these problems by reusing hugepage_vma_check() in > khugepaged_enter_vma_merge(). Lets take a look at this in more detail. This effectively adds the following conditions to khugepaged_enter_vma_merge: - fail if MMF_DISABLE_THP bit is set in mm->flags (good) - allow if merging a tmpfs file and THP tmpfs is enabled (good) - disallow if is_vma_temporary_stack (good) - otherwise, allow if !VM_NO_KHUGEPAGED flag (good) Looks like this covers all the conditions I can think of, and if I missed any, chances are that condition should be added to hugepage_vma_check()... > Signed-off-by: Song Liu <songliubraving@fb.com> Reviewed-by: Rik van Riel <riel@surriel.com> > 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;
On Mon, 21 May 2018, 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(). > > Signed-off-by: Song Liu <songliubraving@fb.com> Acked-by: David Rientjes <rientjes@google.com>
[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?). 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)? > Signed-off-by: Song Liu <songliubraving@fb.com> > --- > 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
On May 22, 2018, at 5:13 AM, Michal Hocko <mhocko@kernel.org> 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 <songliubraving@fb.com> >> --- >> 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
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;
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(). Signed-off-by: Song Liu <songliubraving@fb.com> --- mm/khugepaged.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)