linux-kernel - Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default

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Date:   Wed, 6 Mar 2019 12:44:53 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Dan Williams <dan.j.williams@...el.com>, Oliver <oohall@...il.com>,
        Jan Kara <jack@...e.cz>, linux-nvdimm@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Ross Zwisler <zwisler@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default

On Wed, 06 Mar 2019 14:47:33 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> wrote:

> Dan Williams <dan.j.williams@...el.com> writes:
> 
> > On Thu, Feb 28, 2019 at 1:40 AM Oliver <oohall@...il.com> wrote:  
> >>
> >> On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V
> >> <aneesh.kumar@...ux.ibm.com> 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?

Thanks

Michal