Re: [PATCH v1 05/29] mm/balloon_compaction: make PageOffline sticky until the page is freed

Harry Yoo
2025-07-01T06:17:37Z

On Mon, Jun 30, 2025 at 12:14:01PM -0400, Zi Yan wrote:
> On 30 Jun 2025, at 12:01, Lorenzo Stoakes wrote:
>
> > On Mon, Jun 30, 2025 at 02:59:46PM +0200, David Hildenbrand wrote:
> >> Let the page freeing code handle clearing the page type.
> >
> > Why is this advantageous? We want to keep the page marked offline for longer?
> >
> >>
> >> Acked-by: Zi Yan <ziy@nvidia.com>
> >> Acked-by: Harry Yoo <harry.yoo@oracle.com>
> >> Signed-off-by: David Hildenbrand <david@redhat.com>
> >
> > On assumption this UINT_MAX stuff is sane :)) I mean this is straightforward I
> > guess:
>
> This is how page type is cleared.
> See: https://elixir.bootlin.com/linux/v6.15.4/source/include/linux/page-flags.h#L1013.
>
> I agree with you that patch 4 should have a comment in free_pages_prepare()
> about what the code is for and why UINT_MAX is used.

Or instead of comment, maybe something like this:

/* Clear any page type */
static __always_inline void __ClearPageType(struct page *page)
{
VM_WARN_ON_ONCE_PAGE(!page_has_type(page), page);
page->page_type = UINT_MAX;
}

in patch 4:

if (unlikely(page_has_type(page)))
__ClearPageType(page);

--
Cheers,
Harry / Hyeonggon