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

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Message-Id: <20250503231631.7d8191e51e1d11569b529826@linux-foundation.org>
Date: Sat, 3 May 2025 23:16:31 -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 Sun, 4 May 2025 07:44:40 +0200 Oscar Salvador <osalvador@...e.de> wrote:

> On Sat, May 03, 2025 at 08:03:34PM -0700, Andrew Morton wrote:
> > Why is this a problem?  Is there some bug?  Are these notifications so
> > frequent that there are significant inefficiencies here?
> 
> hi Andrew,
> 
> There is no bug, it is just suboptimal.
> 
> That the numa node state changes were tied to the memory notifier was
> something hacky and that have us bugged for a while now.
> Were mean to tidy that up but just never got around it.
> 
> Actually, first time I brought that up was when I reviewed the first implementation
> of memory demotion (~ca 3-4 years ago now?).
> 
> With the addition of yet another consumer (auto-weitght mempolicy) that was only
> interested in get notified on numa node changes, it became more clear that we
> really want to split those up.

OK, please add to the [0/N].

> > 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.
> 
> That is related to auto-weight mempolicy patches, not to this one.
> I _think_ Gregory means that I take it in as part of the series.

Ah, I'm glad to have company in my confusion ;)