Re: [PATCH v1 10/15] mm/page-flags: reuse PG_slab as PG_anon_exclusive for PageAnon() pages

[Linus Torvalds]

On Fri, Mar 11, 2022 at 10:46 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> -       PG_has_hwpoisoned = PG_mappedtodisk,
> +       PG_has_hwpoisoned = PG_waiters,

That makes me too nervous for words. PG_waiters is very subtle.

Not only is it magical in bit location ways (and the special
clear_bit_unlock_is_negative_byte() macro that *literally* exists only
for unlocking a page), it just ends up having fairly subtle semantics
with intentionally racy clearing etc.

Mixing that up with any hwpoison bits - that aren't used by any normal
mortals and thus get very little coverage - just sounds horribly
horribly wrong.

              Linus