linux-kernel - Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to memoryless nodes

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Message-Id: <20240219192841.f1ed44b8c85073511227721c@linux-foundation.org>
Date: Mon, 19 Feb 2024 19:28:41 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Byungchul Park <byungchul@...com>
Cc: "Huang, Ying" <ying.huang@...el.com>, 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
Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to
 memoryless nodes

On Tue, 20 Feb 2024 11:33:04 +0900 Byungchul Park <byungchul@...com> wrote:

> > Yes, this changelog is missing rather a lot of important information.
> > 
> > I pulled together the below, please check.
> 
> To make it more clear, I need to explain it more. I posted the following
> two patches while resolving the oops issue. However, two are going on
> for different purposes.
> 
> 1) https://lkml.kernel.org/r/20240219041920.1183-1-byungchul@sk.com
> 
>    I started this patch as the fix for the oops. However, I found the
>    root cause comes from using -1 as an array index. So let the root 
>    cause fix go with another thread, 2). Nevertheless, 1) is still
>    necessary as a *reasonable optimization* but not the real fix any
>    more.

Well I altered this patch's changelog to tell readers that it is an
optimization.  But one does wonder why it isn't simply a bugfix. 
Attempting to migrate to a memoryless node is clearly as error. 
Presumably the called code handles it somehow, but in what fashion and
at what cost?

> 2) https://lkml.kernel.org/r/20240216111502.79759-1-byungchul@sk.com
> 
>    I found the root cause of the oops comes from using -1 as an array
>    index. So moved all the oops message, Fixes: tag, and cc stable to
>    here. Long story short, 2) is the *real fix* for the oops.
>