linux-kernel - Re: [PATCHv4 05/13] Documentation/ABI: Add new node sysfs attributes

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Date:   Fri, 18 Jan 2019 13:08:02 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Keith Busch <keith.busch@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCHv4 05/13] Documentation/ABI: Add new node sysfs attributes

On Thu, Jan 17, 2019 at 3:41 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Jan 16, 2019 at 6:59 PM Keith Busch <keith.busch@...el.com> wrote:
> >
> > Add entries for memory initiator and target node class attributes.
> >
> > Signed-off-by: Keith Busch <keith.busch@...el.com>
>
> I would recommend combining this with the previous patch, as the way
> it is now I need to look at two patches at the time. :-)
>
> > ---
> >  Documentation/ABI/stable/sysfs-devices-node | 25 ++++++++++++++++++++++++-
> >  1 file changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> > index 3e90e1f3bf0a..a9c47b4b0eee 100644
> > --- a/Documentation/ABI/stable/sysfs-devices-node
> > +++ b/Documentation/ABI/stable/sysfs-devices-node
> > @@ -90,4 +90,27 @@ Date:                December 2009
> >  Contact:       Lee Schermerhorn <lee.schermerhorn@...com>
> >  Description:
> >                 The node's huge page size control/query attributes.
> > -               See Documentation/admin-guide/mm/hugetlbpage.rst
> > \ No newline at end of file
> > +               See Documentation/admin-guide/mm/hugetlbpage.rst
> > +
> > +What:          /sys/devices/system/node/nodeX/classY/
> > +Date:          December 2018
> > +Contact:       Keith Busch <keith.busch@...el.com>
> > +Description:
> > +               The node's relationship to other nodes for access class "Y".
> > +
> > +What:          /sys/devices/system/node/nodeX/classY/initiator_nodelist
> > +Date:          December 2018
> > +Contact:       Keith Busch <keith.busch@...el.com>
> > +Description:
> > +               The node list of memory initiators that have class "Y" access
> > +               to this node's memory. CPUs and other memory initiators in
> > +               nodes not in the list accessing this node's memory may have
> > +               different performance.
>
> This does not follow the general "one value per file" rule of sysfs (I
> know that there are other sysfs files with more than one value in
> them, but it is better to follow this rule as long as that makes
> sense).
>
> > +
> > +What:          /sys/devices/system/node/nodeX/classY/target_nodelist
> > +Date:          December 2018
> > +Contact:       Keith Busch <keith.busch@...el.com>
> > +Description:
> > +               The node list of memory targets that this initiator node has
> > +               class "Y" access. Memory accesses from this node to nodes not
> > +               in this list may have differet performance.
> > --
>
> Same here.
>
> And if you follow the recommendation given in the previous message
> (add "initiators" and "targets" subdirs under "classX"), you won't
> even need the two files above.

This recommendation is in conflict with Greg's feedback about kobject
usage. If these are just "vanity" subdirs I think it's better to have
a multi-value sysfs file. This "list" style is already commonplace for
the /sys/devices/system hierarchy.