Re: [PATCH 2.6.3-mm3] serialize_writeback_fdatawait patch

Daniel McNeil
2004-02-25T23:01:59Z

On Tue, 2004-02-24 at 17:43, Andrew Morton wrote:

>
> hm, OK. I've converted all the down_read_trylock() things into a sinple
> down_read(), to address the pdflush-busywait problem which Hugh identified.
>

The other thing we could do is add a wbc->encountered_congestion = 1
if the down_read_trylock() fails and then check for that to prevent
the busywait problem.

> This does mean that pdflush can get blocked by ongoing sync activity but
> that's probably insignificant and we have per-spindle pdflush collision
> avoidance which will help a bit.
>
> Call me lazy, but could you please work out the ranking of wb_rwsem with
> respect to the other VFS locks, update the locking documentation in
> mm/filemap.c and make sure that we're actually adhering to it? Thanks.

Ok. I'm looking at this.

Daniel