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Bug 180040 - heavy write with cfq shedulers kills a machine
heavy write with cfq shedulers kills a machine
Status: CLOSED DUPLICATE of bug 180039
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: kernel (Show other bugs)
x86_64 Linux
medium Severity high
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Assigned To: Kernel Maintainer List
Brian Brock
Depends On:
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Reported: 2006-02-04 18:09 EST by Jure Pečar
Modified: 2007-11-30 17:07 EST (History)
0 users

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Doc Type: Bug Fix
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Last Closed: 2006-02-07 11:28:48 EST
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Description Jure Pečar 2006-02-04 18:09:29 EST
From Bugzilla Helper:
User-Agent: Opera/8.5 (X11; Linux i686; U; en)

Description of problem:
Cfq sheduler is the default scheduler in rhel4. I noticed that heavy write 
activity would bring the machine to a halt in a matter of minutes.

I observed this on two different systems now:
1. dual opteron writing to an IBM DS4100 via qlogic 2300
2. dual xeon (ia32) writing to Coraid AoE storage via gigE

Both exhibit the same behaviour. Switching to elevator=deadline fixes the 

Version-Release number of selected component (if applicable):
kernel 2.6.9-22.0.2-ELsmp

How reproducible:

Steps to Reproduce:
1. have a Tb or so of storage attached to the machine (don't know if it really 
matters, but anyway)
2. run something like for i in `seq 1 1000`; do dd if=/dev/zero of=/somewhere/
somefile.$i bs=1M count=1000; done ... where /somewhere is the mountpoint of 
that storage
3. wait

Actual Results:  In 5-15 minutes, the machine becomes totaly unresponsive. What remains in memory 
still runs, everything else is just dead. It's impossible even to login, as it 
just times out.

Expected Results:  Normal writing.

Additional info:

As I mentioned, switching elevator to some other than cfq makes the problem go 
away. I'm not sure that means that cfq is at fault ... it might also be some 
strange interaction of it and default vm settings.
Comment 1 Jason Baron 2006-02-07 11:28:48 EST

*** This bug has been marked as a duplicate of 180039 ***

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