On 4/4/22 22:02, Yang Shi wrote: > The readonly FS THP relies on khugepaged to collapse THP for suitable > vmas. But it is kind of "random luck" for khugepaged to see the > readonly FS vmas (https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@xxxxxxx/) > since currently the vmas are registered to khugepaged when: > - Anon huge pmd page fault > - VMA merge > - MADV_HUGEPAGE > - Shmem mmap > > If the above conditions are not met, even though khugepaged is enabled > it won't see readonly FS vmas at all. MADV_HUGEPAGE could be specified > explicitly to tell khugepaged to collapse this area, but when khugepaged > mode is "always" it should scan suitable vmas as long as VM_NOHUGEPAGE > is not set. > > So make sure readonly FS vmas are registered to khugepaged to make the > behavior more consistent. > > Registering suitable vmas in common mmap path, that could cover both > readonly FS vmas and shmem vmas, so removed the khugepaged calls in > shmem.c. > > Still need to keep the khugepaged call in vma_merge() since vma_merge() > is called in a lot of places, for example, madvise, mprotect, etc. > > Reported-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > --- > mm/mmap.c | 6 ++++++ > mm/shmem.c | 4 ---- > 2 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 604c8dece5dd..616ebbc2d052 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1842,6 +1842,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > } > > vma_link(mm, vma, prev, rb_link, rb_parent); > + > + /* > + * vma_merge() calls khugepaged_enter_vma() either, the below > + * call covers the non-merge case. > + */ > + khugepaged_enter_vma(vma, vma->vm_flags); > /* Once vma denies write, undo our temporary denial count */ > unmap_writable: > if (file && vm_flags & VM_SHARED) > diff --git a/mm/shmem.c b/mm/shmem.c > index 92eca974771d..0c448080d210 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -34,7 +34,6 @@ > #include <linux/export.h> > #include <linux/swap.h> > #include <linux/uio.h> > -#include <linux/khugepaged.h> > #include <linux/hugetlb.h> > #include <linux/fs_parser.h> > #include <linux/swapfile.h> > @@ -2239,7 +2238,6 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma) > > file_accessed(file); > vma->vm_ops = &shmem_vm_ops; > - khugepaged_enter_vma(vma, vma->vm_flags); > return 0; > } > > @@ -4132,8 +4130,6 @@ int shmem_zero_setup(struct vm_area_struct *vma) > vma->vm_file = file; > vma->vm_ops = &shmem_vm_ops; > > - khugepaged_enter_vma(vma, vma->vm_flags); > - > return 0; > } >
