On Thu, Sep 28, 2023 at 01:06:03PM -0400, Jeff Layton wrote: > On Thu, 2023-09-28 at 11:48 -0400, Arnd Bergmann wrote: > > On Thu, Sep 28, 2023, at 07:05, Jeff Layton wrote: > > > This shaves 8 bytes off struct inode, according to pahole. > > > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > > FWIW, this is similar to the approach that Deepa suggested > > back in 2016: > > > > https://lore.kernel.org/lkml/1452144972-15802-3-git-send-email-deepa.kernel@xxxxxxxxx/ > > > > It was NaKed at the time because of the added complexity, > > though it would have been much easier to do it then, > > as we had to touch all the timespec references anyway. > > > > The approach still seems ok to me, but I'm not sure it's worth > > doing it now if we didn't do it then. > > > > I remember seeing those patches go by. I don't remember that change > being NaK'ed, but I wasn't paying close attention at the time > > Looking at it objectively now, I think it's worth it to recover 8 bytes > per inode and open a 4 byte hole that Amir can use to grow the > i_fsnotify_mask. We might even able to shave off another 12 bytes > eventually if we can move to a single 64-bit word per timestamp. I don't think you can, since btrfs timestamps utilize s64 seconds counting in both directions from the Unix epoch. They also support ns resolution: struct btrfs_timespec { __le64 sec; __le32 nsec; } __attribute__ ((__packed__)); --D > It is a lot of churn though. > -- > Jeff Layton <jlayton@xxxxxxxxxx>
