Re: [PATCH RFC] mm: fix refcount check in mapping_evict_folio

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 13, 2024 at 12:58:09PM -0700, Shakeel Butt wrote:
> > +	/*
> > +	 * The refcount will be elevated if any page in the folio is mapped.
> > +	 *
> > +	 * The refcounts break down as follows:
> > +	 * 1 per mapped page
> > +	 * 1 from folio_attach_private, if private is set
> > +	 * 1 from allocating the page in the first place
> > +	 * 1 from the caller
> > +	 */
> 
> I think the above explanation is correct at least from my code
> inspection. Most of the callers are related to memory failure. I would
> reword the "1 per mapped page" to "1 per page in page cache" or
> something as mapped here might mean mapped in page tables.

It's not though.  The "1 from allocating the page in the first place"
is donated to the page cache.  It's late here and I don't have the
ability to work through what's really going on here.