linux-kernel - Re: [PATCH v12 4/7] mm: hotplug: introduce SECTION_CANNOT_OPTIMIZE

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Message-ID: <YoIptjs65NgT1/ed@localhost.localdomain>
Date:   Mon, 16 May 2022 12:38:46 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
        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 v12 4/7] mm: hotplug: introduce
 SECTION_CANNOT_OPTIMIZE_VMEMMAP

On Mon, May 16, 2022 at 06:22:08PM +0800, Muchun Song wrote:
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -913,6 +913,13 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	ms = __nr_to_section(section_nr);
>  	set_section_nid(section_nr, nid);
>  	__section_mark_present(ms, section_nr);
> +	/*
> +	 * Mark whole section as non-optimizable once there is a subsection
> +	 * whose vmemmap pages are allocated from alternative allocator. The
> +	 * early section is always optimizable.
> +	 */
> +	if (!early_section(ms) && altmap)
> +		section_mark_cannot_optimize_vmemmap(ms);

Because no one expects those sections to be removed?
IIRC, early_section + altmap only happened in case of sub-section pmem
scenario? I guess my question is: can we really have early_sections coming
from alternative allocator?

I think this should be spelled out more.


-- 
Oscar Salvador
SUSE Labs