From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Dan Williams <dan.j.williams@intel.com>,
Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH v1] drivers/base/memory.c: Don't store end_section_nr in memory blocks
Date: Wed, 31 Jul 2019 16:04:10 +0200 [thread overview]
Message-ID: <92a8ba85-b913-177c-66a2-d86074e54700@redhat.com> (raw)
In-Reply-To: <58bd9479-051b-a13b-b6d0-c93aac2ed1b3@redhat.com>
On 31.07.19 15:42, David Hildenbrand wrote:
> On 31.07.19 15:25, Michal Hocko wrote:
>> On Wed 31-07-19 15:12:12, David Hildenbrand wrote:
>>> On 31.07.19 14:43, Michal Hocko wrote:
>>>> On Wed 31-07-19 14:22:13, David Hildenbrand wrote:
>>>>> Each memory block spans the same amount of sections/pages/bytes. The size
>>>>> is determined before the first memory block is created. No need to store
>>>>> what we can easily calculate - and the calculations even look simpler now.
>>>>
>>>> While this cleanup helps a bit, I am not sure this is really worth
>>>> bothering. I guess we can agree when I say that the memblock interface
>>>> is suboptimal (to put it mildly). Shouldn't we strive for making it
>>>> a real hotplug API in the future? What do I mean by that? Why should
>>>> be any memblock fixed in size? Shouldn't we have use hotplugable units
>>>> instead (aka pfn range that userspace can work with sensibly)? Do we
>>>> know of any existing userspace that would depend on the current single
>>>> section res. 2GB sized memblocks?
>>>
>>> Short story: It is already ABI (e.g.,
>>> /sys/devices/system/memory/block_size_bytes) - around since 2005 (!) -
>>> since we had memory block devices.
>>>
>>> I suspect that it is mainly manually used. But I might be wrong.
>>
>> Any pointer to the real userspace depending on it? Most usecases I am
>> aware of rely on udev events and either onlining or offlining the memory
>> in the handler.
>
> Yes, that's also what I know - onlining and triggering kexec().
>
> On s390x, admins online sub-increments to selectively add memory to a VM
> - but we could still emulate that by adding memory for that use case in
> the kernel in the current granularity. See
>
> https://books.google.de/books?id=afq4CgAAQBAJ&pg=PA117&lpg=PA117&dq=/sys/devices/system/memory/block_size_bytes&source=bl&ots=iYk_vW5O4G&sig=ACfU3U0s-O-SOVaQO-7HpKO5Hj866w9Pxw&hl=de&sa=X&ved=2ahUKEwjOjPqIot_jAhVPfZoKHcxpAqcQ6AEwB3oECAgQAQ#v=onepage&q=%2Fsys%2Fdevices%2Fsystem%2Fmemory%2Fblock_size_bytes&f=false
>
>>
>> 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
FWIW, powerpc-utils also uses the "removable" property - which means
we're also stuck with that unfortunately. :(
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-07-31 14:04 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 12:22 [PATCH v1] drivers/base/memory.c: Don't store end_section_nr in memory blocks David Hildenbrand
2019-07-31 12:43 ` Michal Hocko
2019-07-31 13:12 ` David Hildenbrand
2019-07-31 13:25 ` Michal Hocko
2019-07-31 13:42 ` David Hildenbrand
2019-07-31 14:04 ` David Hildenbrand [this message]
2019-07-31 14:15 ` Michal Hocko
2019-07-31 14:23 ` David Hildenbrand
2019-07-31 14:14 ` Michal Hocko
2019-07-31 14:21 ` David Hildenbrand
2019-07-31 14:37 ` Michal Hocko
2019-07-31 14:43 ` David Hildenbrand
2019-08-01 6:13 ` Michal Hocko
2019-08-01 7:00 ` David Hildenbrand
2019-08-01 8:27 ` Michal Hocko
2019-08-01 8:36 ` David Hildenbrand
2019-07-31 20:57 ` Andrew Morton
2019-08-01 6:48 ` David Hildenbrand
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