Re: [Patch v4] mm: thp: remove the defer list related code since this will not happen

[Andrew Morton]

On Sat, 18 Jan 2020 07:38:36 +0800 Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> wrote:

> If compound is true, this means it is a PMD mapped THP. Which implies
> the page is not linked to any defer list. So the first code chunk will
> not be executed.
> 
> Also with this reason, it would not be proper to add this page to a
> defer list. So the second code chunk is not correct.
> 
> Based on this, we should remove the defer list related code.
> 
> Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware")
> 
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>    [5.4+]

This patch is identical to "mm: thp: grab the lock before manipulating
defer list", which is rather confusing.  Please let people know when
this sort of thing is done.

The earlier changelog mentioned a possible race condition.  This
changelog does not.  In fact this changelog fails to provide any
description of any userspace-visible runtime effects of the bug. 
Please send along such a description for inclusion, as always.