Trim FastjetJetProducer memory (forward port #9203)

[mark-grimes]

This forward ports some memory improvements found in 6_2_X_SLHC. At 200 pileup it saved ~70Mb memory, there are plots on #9203. Presumably at lower pileup the savings aren't as good.

Note that this is from empirically checking where the memory was being used - there could be other subclasses of VirtualJetProducer that would benefit from a similar fix. I didn't want to touch the fjClusterSeq_ object in the base class because I didn't know how the other subclasses use it - for FastjetJetProducer I can see that it's recreated anew with every event.

At 200 pileup 1/7th of the memory saving was from swapping out the work vectors, and 6/7th was from freeing the fjClusterSeq_ object.

@rappoccio, @lgray

[rappoccio]

This is a good cleanup anyway, so I think it should be included in 75x also.

Cheers,
Sal

[cmsbuild]

A new Pull Request was created by @mark-grimes (Mark Grimes) for CMSSW_7_5_X.

Trim FastjetJetProducer memory (forward port #9203)

It involves the following packages:

RecoJets/JetProducers

@cmsbuild, @cvuosalo, @nclopezo, @slava77 can you please review it and eventually sign? Thanks.
@rappoccio, @jdolen, @ahinzmann, @TaiSakuma, @yslai, @nhanvtran, @schoef, @mariadalfonso this is something you requested to watch as well.
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[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 2deef69
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9206/4922/summary.html

[cvuosalo]

+1

For #9206 927422c

Reduces memory usage by clearing some FastJetProducer objects after they are no longer needed. No change in monitored quantities should occur. #9210 (already approved) is the 74X version of this PR.

The code changes are satisfactory, as are the Jenkins tests. Tests with workflow 25202.0_TTbar_13 against baseline CMSSW_7_5_X_2015-05-20-2300 using 50 events show no significant differences. Similar tests for #9210 show the same. Memory usage seems to go down slightly:

CMSSW_7_5_X_2015-05-20-2300
Summary for 50 events (sizes in MB)
Max VSIZ 3740.59 on evt 33 ; max RSS 3099.75 on evt 28

#9206
Summary for 50 events
Max VSIZ 3719.09 on evt 33 ; max RSS 3086.58 on evt 28

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @nclopezo, @smuzaffar

[davidlange6]

+1