Re: [PATCH] mm: khugepaged: skip huge page collapse for special files

On Wed, Oct 27, 2021 at 12:52:21PM -0700, Yang Shi wrote:

+++ b/mm/khugepaged.c @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma, if (!transhuge_vma_enabled(vma, vm_flags)) return false;

• /* Enabled via shmem mount options or sysfs settings. */
• if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {

• if (vma->vm_file) return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, HPAGE_PMD_NR);

• }

• /* Enabled via shmem mount options or sysfs settings. */
• if (shmem_file(vma->vm_file))

• return shmem_huge_enabled(vma);
  

This doesn't make sense to me. if vma->vm_file, we already returned, so this is dead code.

/* THP settings require madvise. */ if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) return false;

• /* Read-only file mappings need to be aligned for THP to work. */

• /* Only regular file is valid */ if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&

•    !inode_is_open_for_write(vma->vm_file->f_inode) &&
   (vm_flags & VM_EXEC)) {
  

• return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
  

• 		HPAGE_PMD_NR);
  

• struct inode *inode = vma->vm_file->f_inode;
  

• return !inode_is_open_for_write(inode) &&
  

• 	S_ISREG(inode->i_mode);
  

  }

if (!vma->anon_vma || vma->vm_ops) -- 2.26.2