linux-kernel - Re: [PATCH v8 1/4] mm: hugetlb_vmemmap: introduce CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE

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Date:   Wed, 13 Apr 2022 12:08:04 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, mcgrof@...nel.org,
        keescook@...omium.org, yzaikin@...gle.com, osalvador@...e.de,
        david@...hat.com, masahiroy@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v8 1/4] mm: hugetlb_vmemmap: introduce
 CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP

On Wed, 13 Apr 2022 22:47:45 +0800 Muchun Song <songmuchun@...edance.com> wrote:

> If the size of "struct page" is not the power of two but with the feature
> of minimizing overhead of struct page associated with each HugeTLB is
> enabled, then the vmemmap pages of HugeTLB will be corrupted after
> remapping (panic is about to happen in theory).  But this only exists when
> !CONFIG_MEMCG && !CONFIG_SLUB on x86_64.  However, it is not a conventional
> configuration nowadays.  So it is not a real word issue, just the result
> of a code review.

The patch does add a whole bunch of tricky junk to address something
which won't happen.  How about we simply disable
CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP if (!CONFIG_MEMCG &&
!CONFIG_SLUB)?