Re: [PATCH 00/13] writeback bug fixes and simplifications take 2

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

On Thu, Jan 17, 2008 at 11:51:51PM -0800, Michael Rubin wrote:
> On Jan 15, 2008 4:36 AM, Fengguang Wu <wfg@mail.ustc.edu.cn> wrote:
> > Andrew,
> >
> > This patchset mainly polishes the writeback queuing policies.
> > The main goals are:
> >
> > (1) small files should not be starved by big dirty files
> > (2) sync as fast as possible for not-blocked inodes/pages
> >     - don't leave them out; no congestion_wait() in between them
> > (3) avoid busy iowait for blocked inodes
> >     - retry them in the next go of s_io(maybe at the next wakeup of pdflush)
> >
> > The role of the queues:
> >
> > s_dirty:   park for dirtied_when expiration
> > s_io:      park for io submission
> > s_more_io: for big dirty inodes, they will be retried in this run of pdflush
> >            (it ensures fairness between small/large files)
> > s_more_io_wait: for blocked inodes, they will be picked up in next run of s_io
> 
> Quick question to make sure I get this. Each queue is sorted as such:
> 
> s_dirty - sorted by the dirtied_when field
> s_io - sorted by  no explicit key but by the order we want to process
> in sync_sb_inodes
> s_more_io - held for later they are sorted in the same manner as s_io
> 
> Is that it?

Yes, exactly. s_io and s_more_io can be considered as one list broken
up into two - to provide the cursor for sequential iteration.
And s_more_io_wait is simply a container for blocked inodes.