Re: Delayed atime updates ("lazytime")

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

On 11/26/14 10:06, Marcus Reid wrote:
> Hi,
> 
> Looks like Linux is about to grow another solution to handling
> atime updates differently:
> 
> http://lwn.net/SubscriberLink/621046/e59938475fd3e874/
> 
> In short, it will only write out atime changes periodically
> (daily), or if there is another reason to write out the inode, or
> if the inode is about to be pushed out of cache.  This seems like a
> pretty good compromise.
> 
> Currently, the ZFS configuration that results from using
> bsdinstall disables atime on all but /var/mail, which is the only
> example of disabling atime by default that I'm aware of outside of
> Gentoo Linux. I can't seem to find any information that talks about
> the rationale behind that, though a couple things come to mind:
> 
> - some additional IO generated (but that's always been the case) -
> additional wear on SSD devices (enough to compel the change?) - zfs
> snapshot growth (but the snapshot stops growing after one full set
> of inode updates) - wake up otherwise idle spinning media on a
> laptop (the actual reason that was cited as motivation for the
> change)
> 
> Something like lazytime would address most of those concerns, and
> people who are even more OCD than that could disable atime
> completely on their machine.

I think bsdinstall disables atime because it's an "useful default".
The lazytime idea seems to be a better compromise.

PS.  A while back I have implemented a 'relatime' feature on FreeBSD
in a private branch on my github repository, but never have pushed it
further due to a difference in semantics (which needs to be fixed:
atime should still be updated after some time, while my version only
update it once, the Linux semantics is more useful for cleanup
applications to identify unused files) and partially lack of interest
from the community.

Cheers,
- -- 
Xin LI <delphij_at_delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.1
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=I8Cg
-----END PGP SIGNATURE-----