On Thu, 22 Dec 2022 16:39:53 -0800 "Zach O'Keefe" <zokeefe@xxxxxxxxxx> wrote:
> MADV_COLLAPSE acts on one hugepage-aligned/sized region at a time, until
> it has collapsed all eligible memory contained within the bounds
> supplied by the user.
>
> At the top of each hugepage iteration we (re)lock mmap_lock and
> (re)validate the VMA for eligibility and update variables that might
> have changed while mmap_lock was dropped. One thing that might occur,
> is that the VMA could be resized, and as such, we refetch vma->vm_end
> to make sure we don't collapse past the end of the VMA.
>
> However, it's possible that during this refetch that we expand the
> region acted on by MADV_COLLAPSE if vma->vm_end is greater than the end
> of the user-supplied range.
>
> Don't expand the acted-on region when refetching vma->vm_end.
What are the user-visible effects of this?
> Fixes: 4d24de9425f7 ("mm: MADV_COLLAPSE: refetch vm_end after reacquiring mmap_lock")
Should we backport "mm/shmem: restore SHMEM_HUGE_DENY precedence over
MADV_COLLAPSE" and/or this patch into 6.1.x?
