Re: [PATCH 86/87] fs: switch timespec64 fields in inode to discrete integers

Jeff Layton <[email protected]> Thu, 28 Sep 2023 13:06:03 -0400
Newsgroups gmane.comp.file-systems.btrfs,gmane.linux.file-systems,gmane.linux.kernel,gmane.linux.kernel.mm,gmane.linux.ports.ppc64.devel,gmane.linux.drivers.platform.x86.devel,gmane.linux.drivers.rdma,gmane.linux.serial,gmane.linux.usb.general,gmane.linux.kernel.autofs,gmane.comp.file-systems.ceph.devel,gmane.comp.file-systems.coda.general,gmane.linux.kernel.efi,gmane.comp.file-systems.ext4,gmane.linux.file-systems.f2fs,gmane.linux.uml.devel,gmane.linux.drivers.mtd,gmane.linux.nfs,gmane.comp.file-systems.nilfs.user,gmane.linux.file-systems.ntfs.devel,gmane.linux.hardware.karma.devel,gmane.linux.file-systems.union,gmane.comp.file-systems.reiserfs.general,gmane.linux.kernel.cifs,gmane.network.samba.internals,gmane.linux.kernel.bpf,gmane.linux.network,gmane.comp.security.apparmor,gmane.linux.kernel.lsm
Message-ID <[email protected]> 
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 <[email protected]>
> 
> FWIW, this is similar to the approach that Deepa suggested
> back in 2016:
> 
> https://lore.kernel.org/lkml/[email protected]/
> 
> 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. 

It is a lot of churn though.
-- 
Jeff Layton <[email protected]>