Re: [PATCH] mm: Wire up tail page poisoning over ->mappings

[Matthew Wilcox]

On Tue, Aug 15, 2023 at 05:06:59PM -0400, Peter Xu wrote:
> I split this out from another rfc series.  Removed RFC tag because it
> wasn't for this patch but for the documentation updates.  I'll post the rfc
> part alone.  Comments welcomed, thanks.

I still hate it, as I explained here:

https://lore.kernel.org/linux-mm/ZNp7yUgUrIpILnXu@xxxxxxxxxxxxxxxxxxxx/

> > + * When the tail page's mapping field reused, it'll be exempted from
> > + * ->mapping poisoning and checks.  Also see the macro TAIL_MAPPING.
> > + */
> > +#define  TAIL_MAPPING_REUSED_MAX  (2)
> 
> More importantly, I think this is over-parametrisation.  If you start to
> use extra fields in struct folio, just change the code in page_alloc.c
> directly.