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

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Message-ID: <d9db33a5-ca83-13bd-5fcb-5f7d5b3c1bfb@redhat.com>
Date:   Wed, 31 Jul 2019 16:43:58 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
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 31.07.19 16:37, Michal Hocko wrote:
> On Wed 31-07-19 16:21:46, David Hildenbrand wrote:
> [...]
>>> 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.
>>
>> Yeah, but the real question is: who needs it. I can only think about
>> some DIMM scenarios (some, not all). I would be interested in more use
>> cases. Of course, to provide and maintain two APIs we need a good reason.
> 
> Well, my 3TB machine that has 7 movable nodes could really go with less
> than
> $ find /sys/devices/system/memory -name "memory*" | wc -l
> 1729>

The question is if it would be sufficient to increase the memory block
size even further for these kinds of systems (e.g., via a boot parameter
- I think we have that on uv systems) instead of having blocks of
different sizes. Say, 128GB blocks because you're not going to hotplug
128MB DIMMs into such a system - at least that's my guess ;)

> when it doesn't really make any sense to offline less than a
> hotremovable entity which is the whole node effectivelly. I have seen
> reports where a similarly large machine chocked on boot just because of
> too many udev events...>
> In other words allowing smaller granularity is a nice toy but real
> usecases usually work with the whole hotplugable entity (e.g. the whole
> ACPI container).

-- 

Thanks,

David / dhildenb