Re: [PATCH 02/21] mm/hugetlb: correct max_huge_pages accounting on demote

[Andrew Morton]

On Wed, 14 Sep 2022 10:23:05 -0700 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:

> On 09/13/22 12:54, Doug Berger wrote:
> > When demoting a hugepage to a smaller order, the number of pages
> > added to the target hstate will be the size of the large page
> > divided by the size of the smaller page.
> > 
> > Fixes: 8531fc6f52f5 ("hugetlb: add hugetlb demote page support")
> > Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
> > ---
> >  mm/hugetlb.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index e070b8593b37..79949893ac12 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -3472,7 +3472,8 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
> >  	 * based on pool changes for the demoted page.
> >  	 */
> >  	h->max_huge_pages--;
> > -	target_hstate->max_huge_pages += pages_per_huge_page(h);
> > +	target_hstate->max_huge_pages += pages_per_huge_page(h) /
> > +					 pages_per_huge_page(target_hstate);
> >  
> >  	return rc;
> >  }
> 
> This has already been fixed here,
> 
> https://lore.kernel.org/linux-mm/20220823030209.57434-2-linmiaohe@xxxxxxxxxx/

Neither version tells us the user-visible runtime effects of the change :(