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Date: Mon, 19 Feb 2024 19:28:41 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Byungchul Park <byungchul@sk.com>
Cc: "Huang, Ying" <ying.huang@intel.com>, mingo@redhat.com,
 peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org,
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 mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
 linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com
Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to
 memoryless nodes
Message-Id: <20240219192841.f1ed44b8c85073511227721c@linux-foundation.org>
In-Reply-To: <20240220023304.GF65758@system.software.com>
References: <20240219041920.1183-1-byungchul@sk.com>
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On Tue, 20 Feb 2024 11:33:04 +0900 Byungchul Park <byungchul@sk.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.
>