On Mon, Feb 14, 2022 at 11:19:22PM -0800, Christoph Hellwig wrote:
> On Mon, Feb 14, 2022 at 08:00:11PM +0000, Matthew Wilcox (Oracle) wrote:
> > folio_mapped() is expensive because it has to check each page's mapcount
> > field. A cheaper check is whether there are any extra references to
> > the page, other than the one we own and the ones held by the page cache.
> > The call to remove_mapping() will fail in any case if it cannot freeze
> > the refcount, but failing here avoids cycling the i_pages spinlock.
>
> I wonder if something like this should also be in a comment near
> the check in the code.
/* The refcount will be elevated if any page in the folio is mapped */
is what I've added for now.
