Re: [RFC PATCH] mm/page_alloc: fix counting of free pages after take off from buddy

[Ding Hui]

On 2021/4/28 22:54, David Hildenbrand wrote:
> On 21.04.21 04:04, Ding Hui wrote:
> > Recently we found there is a lot MemFree left in /proc/meminfo after
> > do a lot of pages soft offline.
> >
> > I think it's incorrect since NR_FREE_PAGES should not contain HWPoison 
> > pages.
> > After take_page_off_buddy, the page is no longer belong to buddy
> > allocator, and will not be used any more, but we maybe missed accounting
> > NR_FREE_PAGES in this situation.
> >
> > Signed-off-by: Ding Hui <dinghui@xxxxxxxxxxxxxx>
> > ---
> >   mm/page_alloc.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index cfc72873961d..8d65b62784d8 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8947,6 +8947,7 @@ bool take_page_off_buddy(struct page *page)
> >               del_page_from_free_list(page_head, zone, page_order);
> >               break_down_buddy_pages(zone, page_head, page, 0,
> >                           page_order, migratetype);
> > +            __mod_zone_page_state(zone, NR_FREE_PAGES, -1);
> >               ret = true;
> >               break;
> >           }
>
> Should this use __mod_zone_freepage_state() instead?

Yes, you're right.
I'll use it in v2.

--
Thanks,
- Ding Hui