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Date:   Thu, 12 May 2022 20:50:27 +0800
From:   Muchun Song <songmuchun@bytedance.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     corbet@lwn.net, mike.kravetz@oracle.com, akpm@linux-foundation.org,
        mcgrof@kernel.org, keescook@chromium.org, yzaikin@google.com,
        osalvador@suse.de, 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 v10 2/4] mm: memory_hotplug: override memmap_on_memory
 when hugetlb_free_vmemmap=on
Message-ID: <Yn0Ck5isxx4ghQi6@FVFYT0MHHV2J.usts.net>
References: <20220509062703.64249-1-songmuchun@bytedance.com>
 <20220509062703.64249-3-songmuchun@bytedance.com>
 <ebffd794-697b-9bf1-f41b-4b2d52c100fc@redhat.com>
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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.