linux-kernel - Re: [PATCH v5 3/4] x86/vmemmap: Handle unpopulated sub-pmd ranges

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Date:   Tue, 9 Mar 2021 10:39:36 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/4] x86/vmemmap: Handle unpopulated sub-pmd ranges

On 3/9/21 9:41 AM, Oscar Salvador wrote:
> When sizeof(struct page) is not a power of 2, sections do not span
> a PMD anymore and so when populating them some parts of the PMD will
> remain unused.
> Because of this, PMDs will be left behind when depopulating sections
> since remove_pmd_table() thinks that those unused parts are still in
> use.
> 
> Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
> will do the right thing and will let us free the PMD when the last user
> of it is gone.
> 
> This patch is based on a similar patch by David Hildenbrand:
> 
> https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/

Looks good now.  It's much easier to read without the optimization.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>