linux-kernel - Re: [External] Re: [PATCH v17 5/9] mm: hugetlb: set the PageHWPoison to the raw error page

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Date:   Sun, 7 Mar 2021 16:39:07 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v17 5/9] mm: hugetlb: set the PageHWPoison
 to the raw error page

On Sun, Mar 7, 2021 at 4:19 PM Balbir Singh <bsingharora@...il.com> wrote:
>
> On Thu, Feb 25, 2021 at 09:21:26PM +0800, Muchun Song wrote:
> > Because we reuse the first tail vmemmap page frame and remap it
> > with read-only, we cannot set the PageHWPosion on some tail pages.
> > So we can use the head[4].private (There are at least 128 struct
> > page structures associated with the optimized HugeTLB page, so
> > using head[4].private is safe) to record the real error page index
> > and set the raw error page PageHWPoison later.
> >
>
> Does the hardcoding of 4 come from HUGETLB_CGROUP_MIN_ORDER, if so

Yes.

> do we need to hardcode 4? Also, I am not sure about the comment
> on safety and 128 struct pages

We can set head[4].private only if free_vmemmap_pages_per_hpage(h)
returns true. In this case, there are 128 struct page structures (we reserve
2 pages as vmemmap pages, so 2 * 4KB / sizeof(struct page) == 128) that
can be used. Instead of hardcode, I introduce another patch to make the
code more readable. Please refer to patch #8 in this series.

Thanks.

>
> Balbir
>