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.