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

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Message-ID: <20201124102441.GA24718@linux>
Date:   Tue, 24 Nov 2020 11:24:45 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        mhocko@...e.com, song.bao.hua@...ilicon.com,
        duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v6 07/16] x86/mm/64: Disable PMD page mapping of vmemmap

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?

-- 
Oscar Salvador
SUSE L3