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

[Andrew Morton]

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