Re: [Suspend2][ 0/9] Extents support.

Jens Axboe
2006-06-27T07:57:36Z

On Tue, Jun 27 2006, Nigel Cunningham wrote:
> Hi.
>
> On Tuesday 27 June 2006 17:05, Jens Axboe wrote:
> > On Tue, Jun 27 2006, Nigel Cunningham wrote:
> > > On Tuesday 27 June 2006 15:36, Jens Axboe wrote:
> > > > On Tue, Jun 27 2006, Nigel Cunningham wrote:
> > > > > On Tuesday 27 June 2006 07:20, Rafael J. Wysocki wrote:
> > > > > > On Monday 26 June 2006 18:54, Nigel Cunningham wrote:
> > > > > > > Add Suspend2 extent support. Extents are used for storing the
> > > > > > > lists of blocks to which the image will be written, and are
> > > > > > > stored in the image header for use at resume time.
> > > > > >
> > > > > > Could you please put all of the changes in kernel/power/extents.c
> > > > > > into one patch?  It's quite difficult to review them now, at least
> > > > > > for me.
> > > > >
> > > > > I spent a long time splitting them up because I was asked in previous
> > > > > iterations to break them into manageable chunks. How about if I were
> > > > > to email you the individual files off line, so as to not send the
> > > > > same amount again?
> > > >
> > > > Managable chunks means logical changes go together, one function per
> > > > diff is really extreme and unreviewable. Support for extents is one
> > > > logical change, so it's one patch. Unless of course you have to do some
> > > > preparatory patches, then you'd do those separately.
> > > >
> > > > I must admit I thought you were kidding when I read through this
> > > > extents patch series, having a single patch just adding includes!
> > >
> > > Sorry for fluffing it up. I'm pretty inexperienced, but I'm trying to
> > > follow CodingStyle and all the other advice. If I'd known I'd
> > > misunderstood what was wanted, I probably could have submitted this
> > > months ago. Oh well. Live and learn. What would you have me do at this
> > > point?
> >
> > Split up your patches differently, and not in so many steps. Ideally
> > each step should work and compile, with each introducing some sort of
> > functionality. Each patch should be reviewable on its own.
>
> The difficulty I have there is that suspending to disk doesn't seem to
> me to be something where you can add a bit at a time like that. I do
> have proc entries that allow you to say "Just freeze the processes and
> prepare the metadata, then free it and exit" (freezer_test) and "Do
> everything but actually writing the image and doing the atomic copy,
> then exit (test_filter_speed), for diagnosing problems and tuning the
> configuration, but if I start were to start again with nothing, I'd
> only write the dynamic pageflags code to start with and submit it
> (giving you lib/dyn_pageflags.c and kernel/power/pageflags.c), then
> the refrigerator changes and the extent code and so on. I guess what
> I'm trying to say is that I'm not mutating swsusp into suspend2 here,
> and I don't think I can. Suspend2 is a reimplementation of swsusp, not
> a series of incremental modifications. It uses completely different
> methods for writing the image, storing the metadata and so on. Until
> recently, the only thing it shared with swsusp was the refrigerator
> and driver model calls, and even now the sharing of lowlevel code is
> only a tiny fraction of all that is done.

You can't split up what isn't composed of multiple things, of course. I
didn't review your patches (sorry), but if you have changes outside of
suspend2 itself, then you need to split these out. You could submit
those patches seperately.

Now I haven't followed the suspend2 vs swsusp debate very closely, but
it seems to me that your biggest problem with getting this merged is
getting consensus on where exactly this is going. Nobody wants two
different suspend modules in the kernel. So there are two options -
suspend2 is deemed the way to go, and it gets merged and replaces
swsusp. Or the other way around - people like swsusp more, and you are
doomed to maintain suspend2 outside the tree.

> Could I ask what might be a dumb question in this regard - why isn't
> Reiser4 going through the same process? Is it an indication that I
> shouldn't have submitted these patches and should have just asked
> Andrew to take Suspend2 into mm, or is there something different
> between Reiser4 and Suspend2 that I'm missing?

That's not a dumb question at all. reiser4 hasn't been merged for years,
so you probably don't want to look at that as an example :-)

reiser4 is pretty much a separate entity, so it doesn't make sense so
split that up much for submission. Core kernel changes (as always) need
to be split, of course.

Sorry I cannot be of more help.

--
Jens Axboe