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Date:   Tue, 13 Sep 2022 18:07:41 -0700
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Subject: Re: [PATCH 03/21] mm/hugetlb: correct demote page offset logic
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To:     Matthew Wilcox <willy@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Mike Kravetz <mike.kravetz@oracle.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>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        David Hildenbrand <david@redhat.com>, Zi Yan <ziy@nvidia.com>,
        Oscar Salvador <osalvador@suse.de>,
        Hari Bathini <hbathini@linux.ibm.com>,
        Kees Cook <keescook@chromium.org>,
        - <devicetree-spec@vger.kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Mel Gorman <mgorman@suse.de>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-mm@kvack.org, iommu@lists.linux.dev
References: <20220913195508.3511038-1-opendmb@gmail.com>
 <20220913195508.3511038-4-opendmb@gmail.com>
 <YyETeBdbldnoRZ+x@casper.infradead.org>
From:   Doug Berger <opendmb@gmail.com>
In-Reply-To: <YyETeBdbldnoRZ+x@casper.infradead.org>
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On 9/13/2022 4:34 PM, Matthew Wilcox wrote:
> 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.That's good to know. I will include that in v2.

> 
>>   	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))