Re: [PATCH] mm/shmem: restore SHMEM_HUGE_DENY precedence over MADV_COLLAPSE

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On 23.12.22 01:38, Zach O'Keefe wrote:
SHMEM_HUGE_DENY is for emergency use by the admin, to disable allocation
of shmem huge pages if, for example, a dangerous bug is found in their
usage: see "deny" in Documentation/mm/transhuge.rst.  An app using
madvise(,,MADV_COLLAPSE) should not be allowed to override it: restore
its precedence over shmem_huge_force.

Fixes: 7c6c6cc4d3a2 ("mm/shmem: add flag to enforce shmem THP in hugepage_vma_check()")
Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
---
  mm/shmem.c | 6 ++----
  1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index c301487be5fb..0005ab2c29af 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -478,12 +478,10 @@ bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
  	if (vma && ((vma->vm_flags & VM_NOHUGEPAGE) ||
  	    test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)))
  		return false;
-	if (shmem_huge_force)
-		return true;
-	if (shmem_huge == SHMEM_HUGE_FORCE)
-		return true;
  	if (shmem_huge == SHMEM_HUGE_DENY)
  		return false;
+	if (shmem_huge_force || shmem_huge == SHMEM_HUGE_FORCE)
+		return true;
switch (SHMEM_SB(inode->i_sb)->huge) {
  	case SHMEM_HUGE_ALWAYS:

Looks sane to me

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Thanks,

David / dhildenb





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