linux-kernel - Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N

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Date: Wed, 14 Feb 2024 22:13:57 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Byungchul Park <byungchul@...com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	bristot@...hat.com, vschneid@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel_team@...ynix.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set
 N_MEMORY

On Wed, Feb 14, 2024 at 12:53:55PM +0900, Byungchul Park wrote:
> While running qemu with a configuration where some CPUs don't have their
> local memory and with a kernel numa balancing on, the following oops has
> been observed. It's because of null pointers of ->zone_pgdat of zones of
> those nodes that are not initialized at booting time. So should avoid
> nodes not set N_MEMORY from getting promoted.

Looking at free_area_init(), we call free_area_init_node() for each node
found on the system.
And free_area_init_node()->free_area_init_core() inits all zones
belonging to the system via zone_init_internals().
Now, I am not saying the check is wrong because we obviously do not want
migrate memory to a memoryless node, but I am confused as to where
we are crashing.


-- 
Oscar Salvador
SUSE Labs