Re: [RFC PATCH] mm/huge_memory: Do not clobber swp_entry_t during THP split

[Andrew Morton]

On Wed, 19 Oct 2022 11:17:14 -0700 Yang Shi <shy828301@xxxxxxxxx> wrote:

> > The intent of commit b653db77350c patch was to avoid the case where
> > PG_private is clear but folio->private is not-NULL. However, THP tail
> > pages uses page->private for "swp_entry_t if folio_test_swapcache()" as
> > stated in the documentation for struct folio. This patch only clobbers
> > page->private for tail pages if the head page was not in swapcache and
> > warns once if page->private had an unexpected value.
> 
> It looks like the same issue fixed by
> https://lore.kernel.org/linux-mm/20220906190602.1626037-1-bfoster@xxxxxxxxxx/

It is.

As I asked earlier this week, what about reverting b653db77350c?  Why
do we care about the value of ->private for non-PG_private pages?