mm,thp,shmem: make khugepaged obey tmpfs mount flags

Currently if thp enabled=[madvise], mounting a tmpfs filesystem with
huge=always and mmapping files from that tmpfs does not result in
khugepaged collapsing those mappings, despite the mount flag indicating
that it should.

Fix that by breaking up the blocks of tests in hugepage_vma_check a little
bit, and testing things in the correct order.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: c2231020ea7b ("mm: thp: register mm for khugepaged when merging vma for shmem")
Signed-off-by: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xu Yu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 18 insertions, 6 deletions

diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index c941b7377321..2fcc01891b47 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -3,6 +3,7 @@
 #define _LINUX_KHUGEPAGED_H
 
 #include <linux/sched/coredump.h> /* MMF_VM_HUGEPAGE */
+#include <linux/shmem_fs.h>
 
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -57,6 +58,7 @@ static inline int khugepaged_enter(struct vm_area_struct *vma,
 {
 	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
 		if ((khugepaged_always() ||
+		     (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) ||
 		     (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
 		    !(vm_flags & VM_NOHUGEPAGE) &&
 		    !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 75e246f680f4..a7d6cb912b05 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -442,18 +442,28 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
 static bool hugepage_vma_check(struct vm_area_struct *vma,
 			       unsigned long vm_flags)
 {
-	if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
-	    (vm_flags & VM_NOHUGEPAGE) ||
+	/* Explicitly disabled through madvise. */
+	if ((vm_flags & VM_NOHUGEPAGE) ||
 	    test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 		return false;
 
-	if (shmem_file(vma->vm_file) ||
-	    (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
-	     vma->vm_file &&
-	     (vm_flags & VM_DENYWRITE))) {
+	/* Enabled via shmem mount options or sysfs settings. */
+	if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
 		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 				HPAGE_PMD_NR);
 	}
+
+	/* 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. */
+	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
+	    (vm_flags & VM_DENYWRITE)) {
+		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
+				HPAGE_PMD_NR);
+	}
+
 	if (!vma->anon_vma || vma->vm_ops)
 		return false;
 	if (vma_is_temporary_stack(vma))