Re: [PATCH] mm: remove offset check on page->compound_head and folio->lru

Matthew Wilcox
2022-01-08T00:50:15Z

On Fri, Jan 07, 2022 at 04:08:25PM -0800, Andrew Morton wrote:
> On Fri, 7 Jan 2022 22:11:20 +0000 Matthew Wilcox <willy@infradead.org> wrote:
>
> > On Fri, Jan 07, 2022 at 01:40:59PM +0000, Wei Yang wrote:
> > > On Fri, Jan 07, 2022 at 03:59:01AM +0000, Matthew Wilcox wrote:
> > > >On Thu, Jan 06, 2022 at 11:52:54PM +0000, Wei Yang wrote:
> > > >> FOLIO_MATCH() is used to make sure struct page and folio has identical
> > > >> layout for the first several words.
> > > >>
> > > >> The comparison of offset between page->compound_head and folio->lru is
> > > >> more like an internal check in struct page.
> > > >>
> > > >> This patch just removes it.
> > > >>
> > > >> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> > > >
> > > >No.
> > >
> > > Hi, Matthew
> > >
> > > Would you mind sharing some insight on this check?
> >
> > It's right there in the comments.
>
> Well I can't figure out which comment you're referring to?

* WARNING: bit 0 of the first word is used for PageTail(). That
* means the other users of this union MUST NOT use the bit to
* avoid collision and false-positive PageTail().

> > If you can't be bothered to read, why should I write?
>
> I don't think the punishment comes close to fitting the crime here :(

I felt I had to NACk it as quickly as possible so you didn't apply it.
Otherwise I'd've waited until I was back from holiday before replying
to the earlier patch. But you applied that lickety-split, so clearly
I'm not allowed to take a week off.