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Date:   Mon, 16 May 2022 12:38:46 +0200
From:   Oscar Salvador <osalvador@suse.de>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     corbet@lwn.net, mike.kravetz@oracle.com, akpm@linux-foundation.org,
        mcgrof@kernel.org, keescook@chromium.org, yzaikin@google.com,
        david@redhat.com, masahiroy@kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        duanxiongchun@bytedance.com, smuchun@gmail.com
Subject: Re: [PATCH v12 4/7] mm: hotplug: introduce
 SECTION_CANNOT_OPTIMIZE_VMEMMAP
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References: <20220516102211.41557-1-songmuchun@bytedance.com>
 <20220516102211.41557-5-songmuchun@bytedance.com>
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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