On Tue 14-01-20 09:53:54, Ira Weiny wrote:
> On Mon, Jan 13, 2020 at 05:30:04PM -0800, Darrick J. Wong wrote:
> > > > > + error = -EBUSY;
> > > > > + goto out_unlock;
> > > > > + }
> > > > > +
> > > > > error = filemap_write_and_wait(inode->i_mapping);
> > > > > if (error)
> > > > > goto out_unlock;
> > > > > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > > > > index 631f11d6246e..6e7dc626b657 100644
> > > > > --- a/include/linux/fs.h
> > > > > +++ b/include/linux/fs.h
> > > > > @@ -740,6 +740,7 @@ struct inode {
> > > > > #endif
> > > > >
> > > > > void *i_private; /* fs or device private pointer */
> > > > > + atomic64_t i_mapped;
> > > >
> > > > I would have expected to find this in struct address_space since the
> > > > mapping count is a function of the address space, right?
> > >
> > > I suppose but the only external call (above) would be passing an inode. So to
> > > me it seemed better here.
> >
> > But the number of memory mappings reflects the state of the address
> > space, not the inode. Or maybe put another way, if I were an mm
> > developer I would not expect to look in struct inode for mm state.
>
> This is a good point...
>
> >
> > static inline bool inode_has_mappings(struct inode *inode)
> > {
> > return atomic64_read(&inode->i_mapping->mapcount) > 0;
> > }
> >
> > OTOH if there exist other mm developers who /do/ find that storing the
> > mmap count in struct inode is more logical, please let me know. :)
>
> ... My thinking was that the number of mappings does not matters to the mm
> system... However, I'm starting to think you are correct... ;-)
>
> I've made a note of it and we will see what others think.
Well, more importantly mapping != inode. There can be multiple inodes
pointing to the same mapping (struct address_space) as is the case for
example for block devices. So this counter definitely belongs into struct
address_space.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
