Re: [PATCH 0/22] Immutable biovecs, block layer changes

Mike Snitzer
2013-09-27T18:39:23Z

On Tue, Sep 24 2013 at 3:19pm -0400,
Kent Overstreet <kmo@daterainc.com> wrote:

> On Tue, Sep 24, 2013 at 09:20:14AM -0400, Mike Snitzer wrote:
> > On Tue, Sep 24 2013 at 7:00am -0400,
> > Christoph Hellwig <hch@infradead.org> wrote:
> >
> > > Just curious, what's the state of the remaining immutable bio work?
> >
> > Hey Christoph,
> >
> > Have you been over the patchset? Looks sane to you?
> >
> > Given how disruptive this patchset is to the block layer I'm wondering
> > how painful this change will be in combination with Jens' blk-mq
> > changes. I'd prefer to see blk-mq before immutable biovecs; but I have
> > my own selfish reasons for that.
> >
> > I'm also concerned about DM regressions given that a lot of DM code to
> > handle splitting a bio that spans target boundaries is ripped out, see:
> > https://patchwork.kernel.org/patch/2840657/
>
> Oh good, you had seen that :)
>
> Are you worried about performance regressions or actual bugs?

Actual bugs.

> I _have_ explicitly tested that code path, but I don't know what corner
> cases I may have missed so it definitely needs your eyeballs and testing
> too.
>
> As for performance - this'll be more efficient than what the dm code was
> doing before. Especially when the multipage bvec patches go in.

Sure, I can appreciate that.

> > But that is just handwaving/FUD at this point cause I haven't put the
> > time to looking at this patchset close enough to feel comfortable. I
> > can make reviewing this patchset a priority this week though.
> >
> > Kent, have you rebased this patchset at all? Do you have a git tree I
> > can clone to save the pain of pulling these patches out my my mbox,
> > etc.
>
> Yeah: git://evilpiepirate.org/~kent/linux-bcache.git for-jens

Looking now, will build and kickoff some regression tests before I then
jump into reviewing the code.