On Mon, Jan 20, 2025 at 2:31 PM Lance Yang <ioworker0@xxxxxxxxx> wrote:
>
> MADV_PAGEOUT should fail on VMAs with the VM_DROPPABLE flag. While
> MADV_PAGEOUT is intended to move anonymous pages to swap, VM_DROPPABLE
> should not be swapped out.
>
> There is an issue where using MADV_PAGEOUT on a VMA with the VM_DROPPABLE
> flag behaves like MADV_DONTNEED, causing the pages to be dropped. This
> could break the semantics of MADV_PAGEOUT, IMO.
>
> So, let's add a check to detect the VM_DROPPABLE flag before doing
> MADV_PAGEOUT and returns -EINVAL.
>
> Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
> Signed-off-by: Mingzhe Yang <mingzhe.yang@xxxxxx>
> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
I am not convinced this is a correct patch. try_to_unmap_one() will
drop the folio.
madvise_pageout(vma, prev, start, end) will still go to shrink_folio_list() and
try_to_unmap_one().
> ---
> mm/madvise.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 49f3a75046f6..29d0234da8a1 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1263,6 +1263,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> case MADV_COLD:
> return madvise_cold(vma, prev, start, end);
> case MADV_PAGEOUT:
> + if (vma->vm_flags & VM_DROPPABLE)
> + return -EINVAL;
> return madvise_pageout(vma, prev, start, end);
> case MADV_FREE:
> case MADV_DONTNEED:
> --
> 2.45.2
>
Thanks
Barry
