Re: [RFC] [PATCH] A clean aEvgeniy pproach to writeout throttling

Daniel Phillips
2007-12-11T20:07:59Z

On Tuesday 11 December 2007 05:15, Jens Axboe wrote:
> As to the patch in question "fixing" it in the block layer, it's a
> fairly simple work around and I'm not totally against it. If you get
> rid of the ->bi_throttle stuff and just do sanity checks on the
> count, then we could look at getting some testing done.

Oh, sorry I missed that olive branch on first read. Getting rid of
those 8 bytes that bother you requires an extensive rethink of bio
handling in order to make some fields that are not now constant,
constant or at least restored on change. Which would be a good thing
in itself. There are lots of good improvements that can be made to
this subsystem along those lines.

But that is properly a separate project. Quite some time will be needed
to get it right, and should I mention it, everybody needs to be on the
same page or the work will never start. It is therefore a theoretical
solution. We have a practical, tested solution, here and now, and it
is short enough to be understood, unlike any of the previous attempts.

Your argument seems to be that adding 8 bytes to struct bio turns this
beautiful swan into an ugly duck. Actually, because the throttling
reduces the number of bios in flight in a busy system, total memory use
is reduced. When the system is not busy, there are few bios hanging
around so that is not a problem either. Nice, hmm?

Daniel