SRU request for LP#86778 (6.0.6 LTS)

Stefan Bader stefan.bader at canonical.com
Thu Sep 4 14:56:30 UTC 2008


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Tim Gardner wrote:
> Colin Ian King wrote:
>> https://bugs.launchpad.net/ubuntu/dapper/+source/linux-source-2.6.15/+bug/86778
>>
>> SRU Justification:
>>
>> Impact: The mm zone page calculations are being miscalculated because of
>> a previous commit.
>>
>> Fix: Add parentheses around >> operators in setup_per_zone_pages_min()
>> to correct the calculation. Elaboration here:
>>
>> originally the calculation was:
>>
>> zone->pages_low = zone->pages_min + tmp / 4;
>> zone->pages_high = zone->pages_min + tmp / 2;
>>
>> commit 622f7b4c920a9362d506400c0da02e3e06442b27 changed it to:
>>
>> zone->pages_low = zone->pages_min + tmp >> 2;
>> zone->pages_high = zone->pages_min + tmp >> 1;
>>
>> unfortunately the + operator has higher precedence than >> hence the
>> bug.
>>
>> it should be:
>>
>> zone->pages_low = zone->pages_min + (tmp >> 2);
>> zone->pages_high = zone->pages_min + (tmp >> 1);
>>
>> Testcase: One can see the zonelist from /proc/zoneinfo: The low and high
>> water marks should be different between the buggy and fixed versions.
>>
>> Testing:
>>
>> 1. Install 6.0.6 LTS i386 Server in VirtualBox and
>> recording /proc/zoneinfo from /etc/rc.local to capture the zoneline low
>> and high settings at boot time. 
>> 2. Booted up 3 times to see if the figures differ per boot (they
>> don't). 
>> 3. Installed the fixed kernel and repeated the 3 boot test
>> 4. Compare the buggy and fixed /proc/zoneinfo logs, e.g:
>>
>> 	Buggy	Fixed
>> low      15	38
>> high     31	46
>>
>>
>> Attached: Patch, zoneinfo_buggy.log (buggy zoneinfo) and
>> zoneinfo_fixed.log (fixed version).
>>
>>
> 
> ACK. Stefan - are going to package this for upload?
> 
Yes. Coling, are you currently working on something else for 6.06? Otherwise I
would start to get this uploaded.

- --

When all other means of communication fail, try words!


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