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Message-ID: <CAMZfGtWLkYPbz3F-QSNYLOgfwdcTA7iJxG6uvVLCoFtjaBt6nw@mail.gmail.com>
Date: Wed, 21 Apr 2021 17:06:20 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Jonathan Corbet <corbet@....net>,
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Subject: Re: [External] Re: [PATCH v20 8/9] mm: memory_hotplug: disable
memmap_on_memory when hugetlb_free_vmemmap enabled
On Wed, Apr 21, 2021 at 3:33 PM Oscar Salvador <osalvador@...e.de> wrote:
>
> On Wed, Apr 21, 2021 at 11:41:24AM +0800, Muchun Song wrote:
> > > Documentation/admin-guide/kernel-parameters.txt already provides an
> > > explanation on memory_hotplug.memmap_on_memory parameter that states
> > > that the feature cannot be enabled when using hugetlb-vmemmap
> > > optimization.
> > >
> > > Users can always check whether the feature is enabled via
> > > /sys/modules/memory_hotplug/parameters/memmap_on_memory.
>
> Heh, I realized this is not completely true.
> Users can check whether the feature is __enabled__ by checking the sys fs,
> but although it is enabled, it might not be effective.
Right. I have done the test.
>
> This might be due to a different number of reasons, vmemmap does not fully
> span a PMD, the size we want to add spans more than a single memory block, etc.
Agree. Thanks for your explanations.
>
> That is what
>
> "Note that even when enabled, there are a few cases where the feature is not
> effective."
>
> is supposed to mean.
>
> Anyway, I did not change my opionion on this.
>
> Thanks
>
> --
> Oscar Salvador
> SUSE L3
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