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Date:   Wed, 6 Mar 2019 18:15:25 +0530
From:   "Aneesh Kumar K.V" <>
To:     Michal Suchánek <>
Cc:     Dan Williams <>, Oliver <>,
        Jan Kara <>,,
        Linux Kernel Mailing List <>,
        Linux MM <>,
        Ross Zwisler <>,
        Andrew Morton <>,
        linuxppc-dev <>,
        "Kirill A . Shutemov" <>
Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default

On 3/6/19 5:14 PM, Michal Suchánek wrote:
> On Wed, 06 Mar 2019 14:47:33 +0530
> "Aneesh Kumar K.V" <> wrote:
>> Dan Williams <> writes:
>>> On Thu, Feb 28, 2019 at 1:40 AM Oliver <> wrote:
>>>> On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V
>>>> <> wrote:
>> Also even if the user decided to not use THP, by
>> echo "never" > transparent_hugepage/enabled , we should continue to map
>> dax fault using huge page on platforms that can support huge pages.
> Is this a good idea?
> This knob is there for a reason. In some situations having huge pages
> can severely impact performance of the system (due to host-guest
> interaction or whatever) and the ability to really turn off all THP
> would be important in those cases, right?

My understanding was that is not true for dax pages? These are not 
regular memory that got allocated. They are allocated out of /dev/dax/ 
or /dev/pmem*. Do we have a reason not to use hugepages for mapping 
pages in that case?


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