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>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under_nodes()
Date: Fri, 19 Jul 2019 11:18:22 +0200 [thread overview]
Message-ID: <2f0d851e-6edb-4d92-afcd-6c69aa7f45d1@redhat.com> (raw)
In-Reply-To: <20190719090942.GQ30461@dhcp22.suse.cz>
On 19.07.19 11:09, Michal Hocko wrote:
> On Fri 19-07-19 10:48:19, David Hildenbrand wrote:
>> On 19.07.19 10:42, Michal Hocko wrote:
>>> On Thu 18-07-19 16:22:39, David Hildenbrand wrote:
>>>> We don't allow to offline memory block devices that belong to multiple
>>>> numa nodes. Therefore, such devices can never get removed. It is
>>>> sufficient to process a single node when removing the memory block.
>>>>
>>>> Remember for each memory block if it belongs to no, a single, or mixed
>>>> nodes, so we can use that information to skip unregistering or print a
>>>> warning (essentially a safety net to catch BUGs).
>>>
>>> I do not really like NUMA_NO_NODE - 1 thing. This is yet another invalid
>>> node that is magic. Why should we even care? In other words why is this
>>> patch an improvement?
>>
>> I mean we can of course go ahead and drop the "NUMA_NO_NODE - 1" thingy
>> from the patch. A memory block with multiple nodes would (as of now)
>> only indicate one of the nodes.
>
> Yes and that seemed to work reasonably well so far. Sure there is a
> potential confusion but platforms with interleaved nodes are rare enough
> to somebody to even notice so far.
Let's hope there are no BUGs related to that and we just didn't catch
them yet because it's barely used :)
>
>> Then there is simply no way to WARN_ON_ONCE() in case unexpected things
>> would happen. (I mean it really shouldn't happen or we have a BUG
>> somewhere else)
>
> I do not really see much point to warn here. What can user potentially
> do?
We could detect this while testing and see that some other code seems to
do unexpected things (remove such memory blocks although not allowed).
>
>> Alternative: Add "bool mixed_nids;" to "struct memory block".
>
> That would be certainly possible but do we actually care?
Only if we want to warn. And I am fine with dropping this part.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-07-19 9:18 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 14:22 [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under_nodes() David Hildenbrand
2019-07-19 8:14 ` David Hildenbrand
2019-07-19 8:42 ` Michal Hocko
2019-07-19 8:48 ` David Hildenbrand
2019-07-19 9:09 ` Michal Hocko
2019-07-19 9:18 ` David Hildenbrand [this message]
2019-07-19 9:05 ` David Hildenbrand
2019-07-19 9:13 ` Michal Hocko
2019-07-19 9:20 ` David Hildenbrand
2019-07-19 11:36 ` Michal Hocko
2019-07-19 11:42 ` David Hildenbrand
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