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

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

[Zach O'Keefe]

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@google.com>
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Cc: Yang Shi <shy828301@gmail.com>
---
 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:
-- 
2.39.0.314.g84b9a713c41-goog

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

[David Hildenbrand]

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@google.com>
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> Cc: Yang Shi <shy828301@gmail.com>
> ---
>   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@redhat.com>

-- 
Thanks,

David / dhildenb