Re: slab-nomerge (was Re: [git pull] device mapper changes for 4.3)

Mike Snitzer
2015-09-03T00:53:35Z

On Wed, Sep 02 2015 at 8:48pm -0400,
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 2 Sep 2015 16:13:44 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > On Wed, Sep 2, 2015 at 10:39 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> > >
> > > - last but not least: add SLAB_NO_MERGE flag to mm/slab_common and
> > > disable slab merging for all of DM's slabs (XFS will also use
> > > SLAB_NO_MERGE once merged).
> >
> > So I'm not at all convinced this is the right thing to do. In fact,
> > I'm pretty convinced it shouldn't be done this way. Since those
> > commits were at the top of your tree, I just didn't pull them, but
> > took the rest..
>
> I don't have problems with the patch itself, really. It only affects
> callers who use SLAB_NO_MERGE and those developers can make
> their own decisions.
>
> It is a bit sad to de-optimise dm for all users for all time in order
> to make life a bit easier for dm's developers, but maybe that's a
> decent tradeoff.
>
>
> What I do have a problem with is that afaict the patch appeared on
> linux-mm for the first time just yesterday. Didn't cc slab developers,
> it isn't in linux-next, didn't cc linux-kernel or linux-mm or slab/mm
> developers on the pull request. Bad!

Yeap, noted. Won't happen again.

> I'd like the slab developers to have time to understand and review this
> change, please. Partly so they have a chance to provide feedback for
> the usual reasons, but also to help them understand the effect their
> design choice had on client subystems.

Sure, sorry to force the issue like I did.