linux-kernel - Re: [PATCH v5 2/2] mm: memory_hotplug: make hugetlb_optimize_vmemmap compatible with memmap_on

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Message-ID: <YrKPPBGsT25FQFww@localhost.localdomain>
Date:   Wed, 22 Jun 2022 05:40:44 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     akpm@...ux-foundation.org, corbet@....net, david@...hat.com,
        mike.kravetz@...cle.com, paulmck@...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 v5 2/2] mm: memory_hotplug: make hugetlb_optimize_vmemmap
 compatible with memmap_on_memory

On Mon, Jun 20, 2022 at 07:06:16PM +0800, Muchun Song wrote:
> For now, the feature of hugetlb_free_vmemmap is not compatible with the
> feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
> takes precedence over memory_hotplug.memmap_on_memory. However, someone
> wants to make memory_hotplug.memmap_on_memory takes precedence over
> hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
> succeed memory hotplug in close-to-OOM situations.  So the decision
> of making hugetlb_free_vmemmap take precedence is not wise and elegant.
> The proper approach is to have hugetlb_vmemmap.c do the check whether
> the section which the HugeTLB pages belong to can be optimized.  If
> the section's vmemmap pages are allocated from the added memory block
> itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
> otherwise, do the optimization.  Then both kernel parameters are
> compatible.  So this patch introduces VmemmapSelfHosted to mask any
> non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
> to detect if a vmemmap page can be optimized.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Co-developed-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

LGTM, thanks for working on this!


-- 
Oscar Salvador
SUSE Labs