linux-kernel - Re: [PATCH v10 2/4] mm: memory_hotplug: override memmap_on_memory when hugetlb_free

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Message-ID: <Yn0Ck5isxx4ghQi6@FVFYT0MHHV2J.usts.net>
Date:   Thu, 12 May 2022 20:50:27 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
        osalvador@...e.de, 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 v10 2/4] mm: memory_hotplug: override memmap_on_memory
 when hugetlb_free_vmemmap=on

On Thu, May 12, 2022 at 09:36:15AM +0200, David Hildenbrand wrote:
> On 09.05.22 08:27, Muchun Song wrote:
> > Optimizing HugeTLB vmemmap pages is not compatible with allocating memmap on
> > hot added memory. If "hugetlb_free_vmemmap=on" and
> > memory_hotplug.memmap_on_memory" are both passed on the kernel command line,
> > optimizing hugetlb pages takes precedence. 
> 
> Why?
>

Because both two features are not compatible since hugetlb_free_vmemmap cannot
optimize the vmemmap pages allocated from alternative allocator (when
memory_hotplug.memmap_on_memory=1). So when the feature of hugetlb_free_vmemmap
is introduced, I made hugetlb_free_vmemmap take precedence.  BTW, I have a plan
to remove this restriction, I'll post it out ASAP.

Thanks.