linux-kernel - Re: [PATCH v1 0/3] mm/memory_hotplug: Export generic_online

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Message-ID: <20190923085807.GD6016@dhcp22.suse.cz>
Date:   Mon, 23 Sep 2019 10:58:07 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Souptick Joarder <jrdr.linux@...il.com>,
        linux-hyperv@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Oscar Salvador <osalvador@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Qian Cai <cai@....pw>, Sasha Levin <sashal@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v1 0/3] mm/memory_hotplug: Export generic_online_page()

On Fri 20-09-19 10:17:54, David Hildenbrand wrote:
> On 09.09.19 13:48, David Hildenbrand wrote:
> > Based on linux/next + "[PATCH 0/3] Remove __online_page_set_limits()"
> > 
> > Let's replace the __online_page...() functions by generic_online_page().
> > Hyper-V only wants to delay the actual onlining of un-backed pages, so we
> > can simpy re-use the generic function.
> > 
> > Only compile-tested.
> > 
> > Cc: Souptick Joarder <jrdr.linux@...il.com>
> > 
> > David Hildenbrand (3):
> >   mm/memory_hotplug: Export generic_online_page()
> >   hv_balloon: Use generic_online_page()
> >   mm/memory_hotplug: Remove __online_page_free() and
> >     __online_page_increment_counters()
> > 
> >  drivers/hv/hv_balloon.c        |  3 +--
> >  include/linux/memory_hotplug.h |  4 +---
> >  mm/memory_hotplug.c            | 17 ++---------------
> >  3 files changed, 4 insertions(+), 20 deletions(-)
> > 
> 
> Ping, any comments on this one?

Unification makes a lot of sense to me. You can add
Acked-by: Michal Hocko <mhocko@...e.com>

I will most likely won't surprise if I asked for more here though ;)
I have to confess I really detest the whole concept of a hidden callback
with a very weird API. Is this something we can do about? I do realize
that adding a callback would require either cluttering the existing APIs
but maybe we can come up with something more clever. Or maybe existing
external users of online callback can do that as a separate step after
the online is completed - or is this impossible due to locking
guarantees?
-- 
Michal Hocko
SUSE Labs