linux-kernel - Re: [PATCH RFC] mm: Avoid triggering oom-killer during memory hot-remove operations

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Message-ID: <ZqczDQ_qAjOGmBk0@tiehlicka>
Date: Mon, 29 Jul 2024 08:13:33 +0200
From: Michal Hocko <mhocko@...e.com>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>
Subject: Re: [PATCH RFC] mm: Avoid triggering oom-killer during memory
 hot-remove operations

On Mon 29-07-24 02:14:13, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 29/07/2024 08:37, Li Zhijian wrote:
> > Michal,
> > 
> > Sorry to the late reply.
> > 
> > 
> > On 26/07/2024 17:17, Michal Hocko wrote:
> >> On Fri 26-07-24 16:44:56, Li Zhijian wrote:
> >>> When a process is bound to a node that is being hot-removed, any memory
> >>> allocation attempts from that node should fail gracefully without
> >>> triggering the OOM-killer. However, the current behavior can cause the
> >>> oom-killer to be invoked, leading to the termination of processes on other
> >>> nodes, even when there is sufficient memory available in the system.
> >>
> >> But you said they are bound to the node that is offlined.
> >>> Prevent the oom-killer from being triggered by processes bound to a
> >>> node undergoing hot-remove operations. Instead, the allocation attempts
> >>> from the offlining node will simply fail, allowing the process to handle
> >>> the failure appropriately without causing disruption to the system.
> >>
> >> NAK.
> >>
> >> Also it is not really clear why process of offlining should behave any
> >> different from after the node is offlined. Could you describe an actual
> >> problem you are facing with much more details please?
> > 
> > We encountered that some processes(including some system critical services, for example sshd, rsyslogd, login)
> > were killed during our memory hot-remove testing. Our test program are described previous mail[1]
> > 
> > In short, we have 3 memory nodes, node0 and node1 are DRAM, while node2 is CXL volatile memory that is onlined
> > to ZONE_MOVABLE. When we attempted to remove the node2, oom-killed was invoked to kill other processes
> > (sshd, rsyslogd, login) even though there is enough memory on node0+node1.

What are sizes of those nodes, how much memory does the testing program
consumes and do you have oom report without the patch applied?

-- 
Michal Hocko
SUSE Labs