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

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Message-ID: <20190923123008.GP6016@dhcp22.suse.cz>
Date:   Mon, 23 Sep 2019 14:30:08 +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 Mon 23-09-19 14:20:05, David Hildenbrand wrote:
> On 23.09.19 14:07, Michal Hocko wrote:
> > On Mon 23-09-19 13:34:18, David Hildenbrand wrote:
> >> On 23.09.19 13:15, Michal Hocko wrote:
> > [...]
> >>> I am wondering why those pages get onlined when they are, in fact,
> >>> supposed to be offline.
> >>>
> >>
> >> It's the current way of emulating sub-memory-block hotplug on top of the
> >> memory bock device API we have. Hyper-V and XEN have been using that for
> >> a long time.
> > 
> > Do they really have to use the existing block interface when they in
> > fact do not operate on the block granularity? Zone device memory already
> > acts on sub section/block boundaries.
> > 
> 
> Yes, we need memory blocks, especially for user space to properly online
> them (as we discussed a while back, to decide on a zone) and for udev
> events, to e.g., properly reload kexec when memory blocks get
> added/removed/onlined/offlined.

Just to make sure I really follow. We need a user interface to control
where the memory gets onlined but it is the driver which determines
which part of the block really gets onlined, right?
-- 
Michal Hocko
SUSE Labs