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Date:   Wed, 14 Sep 2022 13:58:25 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Doug Berger <opendmb@gmail.com>, Jonathan Corbet <corbet@lwn.net>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Mike Rapoport <rppt@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Borislav Petkov <bp@suse.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
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        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
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        David Hildenbrand <david@redhat.com>, Zi Yan <ziy@nvidia.com>,
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        - <devicetree-spec@vger.kernel.org>,
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Subject: Re: [PATCH 02/21] mm/hugetlb: correct max_huge_pages accounting on
 demote
Message-Id: <20220914135825.88814aa1699e93c8a782abc6@linux-foundation.org>
In-Reply-To: <YyIN+bpKdCb3JuuY@monkey>
References: <20220913195508.3511038-1-opendmb@gmail.com>
        <20220913195508.3511038-3-opendmb@gmail.com>
        <YyIN+bpKdCb3JuuY@monkey>
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On Wed, 14 Sep 2022 10:23:05 -0700 Mike Kravetz <mike.kravetz@oracle.com> 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@gmail.com>
> > ---
> >  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@huawei.com/

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