linux-kernel - Re: [PATCH v1] drivers/base/memory.c: Don't store end_section

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Message-ID: <20190731141411.GU9330@dhcp22.suse.cz>
Date:   Wed, 31 Jul 2019 16:14:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1] drivers/base/memory.c: Don't store end_section_nr in
 memory blocks

On Wed 31-07-19 15:42:53, David Hildenbrand wrote:
> On 31.07.19 15:25, Michal Hocko wrote:
[...]
> > I know we have documented this as an ABI and it is really _sad_ that
> > this ABI didn't get through normal scrutiny any user visible interface
> > should go through but these are sins of the past...
> 
> A quick google search indicates that
> 
> Kata containers queries the block size:
> https://github.com/kata-containers/runtime/issues/796
> 
> Powerpc userspace queries it:
> https://groups.google.com/forum/#!msg/powerpc-utils-devel/dKjZCqpTxus/AwkstV2ABwAJ
> 
> I can imagine that ppc dynamic memory onlines only pieces of added
> memory - DIMMs AFAIK (haven't looked at the details).
> 
> There might be more users.

Thanks! I suspect most of them are just using the information because
they do not have anything better.

Thinking about it some more, I believe that we can reasonably provide
both APIs controlable by a command line parameter for backwards
compatibility. It is the hotplug code to control sysfs APIs.  E.g.
create one sysfs entry per add_memory_resource for the new semantic.

It is some time since I've checked the ACPI side of the matter but that
code shouldn't really depend on a particular size of the memblock
either when trigerring udev events. I might be wrong here of course.
-- 
Michal Hocko
SUSE Labs