Re: [GIT PULL] Fsnotify cleanups

[Jan Kara <jack@suse.cz>]

On Sun 10-06-18 20:49:16, Amir Goldstein wrote:
> On Sat, Jun 9, 2018 at 9:46 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> > On Sat, Jun 9, 2018 at 8:30 PM, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> >> On Fri, Jun 8, 2018 at 11:57 PM Amir Goldstein <amir73il@gmail.com> wrote:
> >>>
> >>> We embed fsnotify_obj in struct inode and fsnotify_obj_mask in struct mount.
> >>
> >> So I'd *really* like to see just a pointer, not an embedded struct.
> >>
> >> Yes, if you get rid of the mask from the embedded struct (so that it
> >> only contains a pointer), you do get rid of the odd alignment issues
> >> and the need for "packed".
> >>
> >> But from previous experience, once you embed a structure, that
> >> structure tends to grow. Because it can, and it's so convenient.
> >> Suddently it has a spinlock in it too etc.
> >>
> >
> > Fair enough.
> >
> >> So if you can make do with just the pointer, it would actually be
> >> nicer to expose it as such. Then you can also avoid the header file
> >> dependency chain, because you can just pre-declare the structure (like
> >> it does now) and
> >>
> >>     struct fsnotify_mark_connector;
> >>     ..
> >>         struct fsnotify_mark_connector __rcu    *i_fsnotify_marks;
> >>
> >> in the inode. That way the core header files don't need to worry about
> >> the fsnotify details, and don't need to include fsnotify headers.
> >>
> >> And we can do inode packing without having to know (not that it
> >> happens all that often - everybody would *love* to shrink the inode
> >> structure, but it's just hard. Because everybody also wants to put
> >> their own data into the inode ..)
> >>
> >> Can't the generalization code just take a pointer to a __rcu pointer
> >> to fsnotify_mark_connector, obviating the need for the fsnotify_obj
> >> structure definition?
> >>
> >
> 
> Jan,
> 
> I reworked the cleanup patches to get rid of fsnotify_obj and pushed to:
> https://github.com/amir73il/linux.git fsnotify-cleanup

Thanks!

> Only last 5 patches from fsnotify_for_v4.18-rc1 have been modified
> and I removed your S-O-B from the modified patches.
> 
> This leaves struct inode unchanged, in fact no changes to code outside
> fsnotify/audit at all.
> 
> mask is now a member of connector for the purpose of generalizing
> add/remove mark, but struct inode/mount still have a copy of the mask
> for the purpose of the VFS optimizations.

Looking through those patches, is it really beneficial to add mask to
connector when you keep it in inode / vfsmount? A helper function to get
mask from connector would make the same refactoring possible as well, won't
it?

And adding a helper function to set mask given connector would get rid of
the remaining checks for connector type due to mask manipulations...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR