Re: Lazytime feature bugs

[Theodore Ts'o <tytso@mit.edu>]

On Thu, Feb 26, 2015 at 09:34:55AM +0100, Jan Kara wrote:
>   I don't think you can reset i_dirty_time_when to "now" in b) because in
> that case continually dirtied files won't ever have timestamps written (you
> are completely loosing track of when you last wrote timestamps to disk).

In the case of continually dirtied files, in my proposal we would be
checking to see if i_dirty_time_when is older when we scan files in
b_io, which means that we would discover files with stale timestamps
on disk, and they would get written out.  This was the same as (4) in
your propsal:


> 4) When processing inodes on b_io list we also check whether
>    i_dirty_time_when is older than 12 hours. If so, we writeout inode.

But your mechanism would work as well; I preferred to keep
i_dirty_when to only mean when the pages were dirtied, but the
important thing is that we have to track when the timestamps were
dirtied and when the pages were dirtied as separate things.

> BTW, I prefer to really keep the timestamp updates within 24 hours. IMHO
> it's easier for humans and it's not like there's any performance difference
> in possibly writing inodes every 12 hours instead of every 24 hours.

I agree, writing inodes ever 12 hours so that the worst case staleness
is 24 hours is fair enough.  If we really cared we could make the
duration tunable, but I agree that whether we use 12 or 24 hours, with
the worst case being 24 or 48 hours, is probably not going to result
in a measurable performance difference.

Cheers,

					- Ted