On Tue, Mar 23, 2021 at 03:41:25PM +0000, Christoph Hellwig wrote:
> On Mon, Mar 22, 2021 at 01:19:07AM +0000, Matthew Wilcox wrote:
> > I'd like to get it down to zero. After all, the !mapping case in
> > set_page_dirty() is exactly what we want. So is there a problem
> > with doing this?
> >
> > +++ b/mm/page-writeback.c
> > @@ -2562 +2562 @@ int set_page_dirty(struct page *page)
> > - if (likely(mapping)) {
> > + if (likely(mapping && mapping_can_writeback(mapping))) {
> >
> > But then I noticed that we have both mapping_can_writeback()
> > and mapping_use_writeback_tags(), and I'm no longer sure
> > which one to use. Also, why don't we mirror the results of
> > inode_to_bdi(mapping->host)->capabilities & BDI_CAP_WRITEBACK into
> > a mapping->flags & AS_something bit?
>
> Probably because no one has bothered to submit a patch yet.
I was hoping for a little more guidance. Are mapping_can_writeback()
and mapping_use_writeback_tags() really the same thing? I mean,
obviously the swap spaces actually _can_ writeback, but it doesn't
use the tags to do it.
