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



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.


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