linux-kernel - Re: [PATCH v3 0/3] Implement numa node notifier

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Message-Id: <20250503200334.3f912eeb7ca484bca4eec7fd@linux-foundation.org>
Date: Sat, 3 May 2025 20:03:34 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Oscar Salvador <osalvador@...e.de>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>, Hyeonggon
 Yoo <42.hyeyoo@...il.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Rakie Kim <rakie.kim@...com>
Subject: Re: [PATCH v3 0/3] Implement numa node notifier

On Fri,  2 May 2025 10:36:21 +0200 Oscar Salvador <osalvador@...e.de> wrote:

> Memory notifier is a tool that allow consumers to get notified whenever
> memory gets onlined or offlined in the system.
> Currently, there are 10 consumers of that, but 5 out of those 10 consumers
> are only interested in getting notifications when a numa node changes its
> memory state.
> That means going from memoryless to memory-aware of vice versa.
> 
> Which means that for every {online,offline}_pages operation they get
> notified even though the numa node might not have changed its state.

Why is this a problem?  Is there some bug?  Are these notifications so
frequent that there are significant inefficiencies here?

Further down-thread, Gregory tells us that Dan's patch "seems to fix
the underlying problem", but nobody (including Dan) told us about any
"problem" at all.