linux-kernel - Re: [PATCH 03/21] mm/hugetlb: correct demote page offset logic

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Message-ID: <YyETeBdbldnoRZ+x@casper.infradead.org>
Date:   Wed, 14 Sep 2022 00:34:16 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Doug Berger <opendmb@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Rapoport <rppt@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Oscar Salvador <osalvador@...e.de>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        - <devicetree-spec@...r.kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
        Mel Gorman <mgorman@...e.de>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux.dev
Subject: Re: [PATCH 03/21] mm/hugetlb: correct demote page offset logic

On Tue, Sep 13, 2022 at 12:54:50PM -0700, Doug Berger wrote:
> With gigantic pages it may not be true that struct page structures
> are contiguous across the entire gigantic page. The mem_map_offset
> function is used here in place of direct pointer arithmetic to
> correct for this.

We're just eliminating mem_map_offset().  Please use nth_page()
instead.

>  	for (i = 0; i < pages_per_huge_page(h);
>  				i += pages_per_huge_page(target_hstate)) {
> +		subpage = mem_map_offset(page, i);
>  		if (hstate_is_gigantic(target_hstate))