On Thu, 2023-10-05 at 08:08 +0300, Amir Goldstein wrote:
> On Wed, Oct 4, 2023 at 9:56 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> >
> > The recent change to use discrete integers instead of struct timespec64
> > shaved 8 bytes off of struct inode, but it also moves the i_lock
> > into the previous cacheline, away from the fields that it protects.
> >
> > Move i_generation above the i_lock, which moves the new 4 byte hole to
> > just after the i_fsnotify_mask in my setup.
>
> Might be good to mention that this hole has a purpose...
>
> >
> > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > include/linux/fs.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 485b5e21c8e5..686c9f33e725 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -677,6 +677,7 @@ struct inode {
> > u32 i_atime_nsec;
> > u32 i_mtime_nsec;
> > u32 i_ctime_nsec;
> > + u32 i_generation;
> > spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
> > unsigned short i_bytes;
> > u8 i_blkbits;
> > @@ -733,7 +734,6 @@ struct inode {
> > unsigned i_dir_seq;
> > };
> >
> > - __u32 i_generation;
> >
> > #ifdef CONFIG_FSNOTIFY
> > __u32 i_fsnotify_mask; /* all events this inode cares about */
>
> If you post another version, please leave a comment here
>
> + /* 32bit hole reserved for expanding i_fsnotify_mask to 64bit */
>
Sure.
I suppose we could create a union there too if you really want to
reserve it:
union {
__u32 i_fsnotify_mask;
__u64 __i_fsnotify_mask_ext;
};
--
Jeff Layton <jlayton@xxxxxxxxxx>
