[PATCH 3/3] mm,thp,shmem: make khugepaged obey tmpfs mount flags

[Rik van Riel]

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.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Fixes: c2231020ea7b ("mm: thp: register mm for khugepaged when merging vma for shmem")
---
 include/linux/khugepaged.h |  2 ++
 mm/khugepaged.c            | 22 ++++++++++++++++------
 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 4e3dff13eb70..abab394c4206 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -440,18 +440,28 @@ 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))
-- 
2.25.4