linux-kernel - Re: [PATCH] mm/hugetlb: correct demote page offset logic

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Message-ID: <YyJFQaZtZr08fMhj@monkey>
Date:   Wed, 14 Sep 2022 14:18:57 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Doug Berger <opendmb@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Oscar Salvador <osalvador@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: correct demote page offset logic

On 09/14/22 12:09, Doug Berger wrote:
> With gigantic pages it may not be true that struct page structures
> are contiguous across the entire gigantic page. The nth_page macro
> is used here in place of direct pointer arithmetic to correct for
> this.
> 
> Fixes: 8531fc6f52f5 ("hugetlb: add hugetlb demote page support")
> Signed-off-by: Doug Berger <opendmb@...il.com>
> Cc: <stable@...r.kernel.org>
> ---
>  mm/hugetlb.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)

Thanks!

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

To answer Andrew's question about user-visible runtime effects.
We could get addressing exceptions.  However, this is only possible in
configurations where CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_VMEMMAP.
Such a configuration option is rare an unknown to be the default
anywhere.
-- 
Mike Kravetz