Re: Lazytime feature bugs

[Jan Kara <jack@suse.cz>]

On Thu 26-02-15 08:45:53, Ted Tso wrote:
> 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.
  But you wrote you'll reset i_dirty_time_when to "now" when queueing into
b_dirty_time. Thus frequently dirtied inodes will just travel back and
forth between b_dirty and b_dirty_time lists and i_dirty_time will be
continuously reset. And you never end up writing it. That's why I suggested
to reset i_dirted_when instead (since it would be unused in b_dirty_time
list anyway).

> 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.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR