Re: [ndctl PATCH 04/10] libdaxctl: add an API to determine if memory is movable

[Dan Williams <dan.j.williams@intel.com>]

On Fri, Oct 18, 2019 at 12:57 PM Verma, Vishal L
<vishal.l.verma@intel.com> wrote:
>
>
> On Fri, 2019-10-18 at 11:54 -0700, Dan Williams wrote:
> > On Wed, Oct 2, 2019 at 4:49 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > > By default, daxctl always attempts to online new memory sections as
> > > 'movable' so that routine kernel allocations aren't serviced from this
> > > memory, and the memory is later removable via hot-unplug.
> > >
> > > System configuration, or other agents (such as udev rules) may race
> > > 'daxctl' to online memory, and this may result in the memory not being
> > > 'movable'. Add an interface to query the movability of a memory object
> > > associated with a dax device.
> > >
> > > This is in preparation to both display a 'movable' attribute in device
> > > listings, as well as optionally allowing memory to be onlined as
> > > non-movable.
> > >
> > > Cc: Dan Williams <dan.j.williams@intel.com>
> > > Reported-by: Ben Olson <ben.olson@intel.com>
> > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > > ---
> > >  daxctl/lib/libdaxctl-private.h | 20 +++++++++
> > >  daxctl/lib/libdaxctl.c         | 77 ++++++++++++++++++++++++++++++++--
> > >  daxctl/lib/libdaxctl.sym       |  5 +++
> > >  daxctl/libdaxctl.h             |  1 +
> > >  4 files changed, 100 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/daxctl/lib/libdaxctl-private.h b/daxctl/lib/libdaxctl-private.h
> > > index 7ba3c46..82939bb 100644
> > > --- a/daxctl/lib/libdaxctl-private.h
> > > +++ b/daxctl/lib/libdaxctl-private.h
> > > @@ -44,6 +44,25 @@ enum memory_op {
> > >         MEM_SET_ONLINE,
> > >         MEM_IS_ONLINE,
> > >         MEM_COUNT,
> > > +       MEM_FIND_ZONE,
> >
> > This is private so the naming is not too big a concern, but isn't this
> > a MEM_GET_ZONE? A find operation to me is something that can succeed
> > to find nothing, whereas a get operation fail assumes the association
> > can always be retrieved barring exceptional conditions.
>
> Hm, my personal view of find vs. get was that 'get' grabs a reference
> (or similar) to something which we know how to get to (have a pointer
> directly) etc.

Oh, that's get as in get/put. I'm talking about get/set. Where the
zone is a property memblock that can set and retrieved.

> 'Find' is more of a 'go searching for' something - and it
> may involve walking and looping over data structures.
>
> But I'm not too opposed to this, and can change to 'get' if that follows
> convention better.

Like I said it's private, so it's not a big deal (i.e. API users won't
see it), but ndctl does have a few apis that walk and loop over data
structures using a get verb, or the ones that retrieve the dynamic
state of a sysfs attribute.

I will grant you that in hindsight some of the "get_by" apis might
have been better named "find".
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