linux-kernel - Re: [External] Re: [PATCH v6 07/16] x86/mm/64: Disable PMD page mapping of vmemmap

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Date:   Tue, 24 Nov 2020 19:13:47 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, 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>, 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>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.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 v6 07/16] x86/mm/64: Disable PMD page
 mapping of vmemmap

On Tue, Nov 24, 2020 at 6:24 PM Oscar Salvador <osalvador@...e.de> wrote:
>
> On Tue, Nov 24, 2020 at 05:52:50PM +0800, Muchun Song wrote:
> > If we enable the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, we can just
> > disbale PMD page mapping of vmemmap to simplify the code. In this
> > case, we do not need complex code doing vmemmap page table
> > manipulation. This is a way to simply the first version of this
> > patch series. In the future, we can add some code doing page table
> > manipulation.
>
> IIRC, CONFIG_HUGETLB_PAGE_FREE_VMEMMAP was supposed to be enabled by default,
> right?
> And we would control whether we __really__ want to this by a boot option,
> which was disabled by default?
>
> If you go for populating the memmap with basepages by checking
> CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, would not everybody, even the ones that
> did not enable this by the boot option be affected?

Yeah, this should be improved. We should enable the basepage mapping
of vmemmap only when this feature is enabled via boot command line.
I will apply the suggestions mentioned by Barry. Thanks.

>
> --
> Oscar Salvador
> SUSE L3



-- 
Yours,
Muchun