On Tue, May 11, 2021 at 10:47:18PM +0100, Matthew Wilcox (Oracle) wrote: > This is the folio equivalent of page_mapcount(). [...] > > +/** > + * folio_mapcount - The number of mappings of this folio. > + * @folio: The folio. > + * > + * The result includes the number of times any of the pages in the > + * folio are mapped to userspace. I thought it did, but it doesn't. It returns the number of times the head/base page of this folio is mapped into userspace, which is not a terribly useful concept. I suspect this should call total_mapcount() instead. Looking through the complete set of patches, it's only used in debugging code (unaccount_page_cache_page() and dump_page()). I'm going to withdraw this patch from the next submission until I've had the chance to think about it some more.
