Re: [PATCH v2] mm/page_alloc: fix counting of free pages after take off from buddy

[Ding Hui]

On 2021/5/25 16:32, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Sat, May 08, 2021 at 11:55:33AM +0800, 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.
> > For offline free pages, after a successful call take_page_off_buddy(), the
> > page is no longer belong to buddy allocator, and will not be used any more,
> > but we missed accounting NR_FREE_PAGES in this situation.
> >
> > Do update like rmqueue() does.
> >
> > Signed-off-by: Ding Hui <dinghui@xxxxxxxxxxxxxx>
> > ---
> > V2:
> > use __mod_zone_freepage_state instead of __mod_zone_page_state
> >
> >   mm/page_alloc.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index cfc72873961d..e124a615303b 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_freepage_state(zone, -1, migratetype);
>
> Page offline code (see set_migratetype_isolate()) seems to handle
> NR_FREE_PAGES counter in its own way, so I think that it's more correct to
> call __mod_zone_freepage_state() only when is_migrate_isolate(migratetype))
> is false.
>
> Otherwise, the patch looks good to me.

Thanks for reply and suggestion, I'll send v3 patch later.

> >   			ret = true;
> >   			break;
> >   		}
> > --
> > 2.17.1


--
Thanks,
- Ding Hui