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

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Date:   Wed, 14 Sep 2022 10:54:27 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        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>,
        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>,
        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 9/14/2022 10:08 AM, Mike Kravetz wrote:
> On 09/13/22 18:07, Doug Berger wrote:
>> 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.
> 
> Thanks Doug and Matthew.  I will take a closer look at this series soon.
> 
> It seems like this patch is a fix independent of the series.  If so, I
> would suggest sending separate to make it easy for backports to stable.
Yes, as I noted in [PATCH 00/21] the first three patches fit that 
description, but I included them here in case someone was brave enough 
to attempt to use this patch set. They were in my branch for my own testing.

Full disclosure: An earlier version of this patch set had more complete 
support for hugepage isolation that included migrating the isolation 
state when demoting a hugepage that touched lines in 
demote_free_huge_page() and depended on the subpage variable introduced 
here.

At this point I will submit a patch for this on its own and will likely 
remove the first three commits when submitting V2 of the set.

Thanks for your consideration.
-Doug