linux-kernel - Re: [PATCH, RFC 1/2] Add config option to enable FS/DAX PMD sharing

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Message-ID: <CAPcyv4juGEo=sMX01YuqPY9oYDjBjmRp7GvreNnX8YvKQz=SjA@mail.gmail.com>
Date:   Fri, 10 May 2019 11:14:07 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>
Cc:     Larry Bassel <larry.bassel@...cle.com>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH, RFC 1/2] Add config option to enable FS/DAX PMD sharing

On Fri, May 10, 2019 at 9:32 AM Elliott, Robert (Servers)
<elliott@....com> wrote:
>
>
>
> > -----Original Message-----
> > From: Linux-nvdimm <linux-nvdimm-bounces@...ts.01.org> On Behalf Of
> > Larry Bassel
> > Sent: Thursday, May 09, 2019 11:06 AM
> > Subject: [PATCH, RFC 1/2] Add config option to enable FS/DAX PMD
> > sharing
> >
> > If enabled, sharing of FS/DAX PMDs will be attempted.
> >
> ...
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> ...
> >
> > +config MAY_SHARE_FSDAX_PMD
> > +def_bool y
> > +
>
> Is a config option really necessary - is there any reason to
> not choose to do this?

Agree. Either the arch implementation supports it or it doesn't, I
don't see a need for any further configuration flexibility. Seems
ARCH_WANT_HUGE_PMD_SHARE should be renamed ARCH_HAS_HUGE_PMD_SHARE and
then auto-enable it.