linux-kernel - Re: [PATCH] mm: use-once cleanup

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Message-ID: <44C8D165.3060803@shadowen.org>
Date:	Thu, 27 Jul 2006 15:44:53 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	"Martin J. Bligh" <mbligh@...igh.org>
CC:	Andrew Morton <akpm@...l.org>, Rik van Riel <riel@...hat.com>,
	a.p.zijlstra@...llo.nl, linux-mm@...ck.org, torvalds@...l.org,
	piggin@...erone.com.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: use-once cleanup

Martin J. Bligh wrote:
> 
>>> 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.

I'll happily run it through the test suites once I get my machines 
working again after 2.6.18-rc2-mm1 has finished with them :(.

-apw
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