Re: [PATCH] mm: use-once cleanup

["Martin J. Bligh" <mbligh@mbligh.org>]

> > Peter Zijlstra wrote:
> >    
> >
> > > Hi,
> > >
> > > This is yet another implementation of the PG_useonce cleanup spoken of
> > > during the VM summit.
> > >      
> > After getting bitten by rsync yet again, I guess it's time to insist
> > that this patch gets merged...
> >
> > Andrew, could you merge this?  Pretty please? ;)
> >
> >    
>
> Guys, this is a performance patch, right?
>
> One which has no published performance testing results, right?
>
> It would be somewhat odd to merge it under these circumstances.
>
> And this applies to all of these
> hey-this-is-cool-but-i-didnt-bother-testing-it MM patches which people are
> throwing around.  This stuff is *hard*.  It has a bad tendency to cause
> nasty problems which only become known months after the code is merged.
>
> I shouldn't have to describe all this, but
>
> - Identify the workloads which it's supposed to improve, set up tests,
>  run tests, publish results.
>
> - Identify the workloads which it's expected to damage, set up tests, run
>  tests, publish results.
>
> - Identify workloads which aren't expected to be impacted, make a good
>  effort at demonstrating that they are not impacted.
>
> - Perform stability/stress testing, publish results.
>
> Writing the code is about 5% of the effort for this sort of thing.
>
> Yes, we can toss it in the tree and see what happens.  But it tends to be
> the case that unless someone does targetted testing such as the above,
> regressions simply aren't noticed for long periods of time.  <wonders which
> schmuck gets to do the legwork when people report problems>
>
> Just the (unchangelogged) changes to the when-to-call-mark_page_accessed()
> logic are a big deal.  Probably these should be a separate patch -
> separately changelogged, separately tested, separately justified.
>
> Performance testing is *everything* for this sort of patch and afaict none
> has been done, so it's as if it hadn't been written, no?
> -
>
>  
Rik / Peter ... I lost the original mail + patch, but if you put it
up on a URL somewhere, Andy would probably run it through the test
harness for at least some basic perf testing, if you ask him ;-)
Probably against mainline, not -mm, as -mm seems to have other
problems right now.

M.



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