Delayed atime updates ("lazytime")
delphij at delphij.net
Wed Nov 26 20:30:23 UTC 2014
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On 11/26/14 10:06, Marcus Reid wrote:
> Looks like Linux is about to grow another solution to handling
> atime updates differently:
> 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
> 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.
Xin LI <delphij at delphij.net> https://www.delphij.net/
FreeBSD - The Power to Serve! Live free or die
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