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Are dcachesize values supposed to be 0's? [message #27059]

Thu, 07 February 2008 17:20

dowdle
Messages: 261
Registered: December 2005
Location: Bozeman, Montana

Senior Member

I haven't had any problems as a result of this... but looking at the UBC output from a few different machines I notice that several of them have 0 values in the held and maxheld values for dcachesize. This seems odd. Should dcachesize have 0 values?

There didn't seem to be any pattern to when it would be zero and when it wouldn't be 0. I have two machines that are exactly alike in hardware and software... and even VPSes... and one has non-0 values for dcachesize and the other has 0's.

Example output from two similar hardware nodes:

[root@backup1 ~]# grep dcachesize /proc/user_beancounters
            dcachesize        65844      90801    9985491   10285056          0
            dcachesize      1696690    1863838 2147483647 2147483647          0

[root@backup2 ~]# grep dcachesize /proc/user_beancounters
            dcachesize            0          0    9985491   10285056          0
            dcachesize            0          0 2147483647 2147483647          0

Questions:

1) Should the held and maxheld columns for dcachesize ever be 0

2) If yes to #1, why?

3) If no to #2, want me to file a bug report?

--
TYL, Scott Dowdle
Belgrade, Montana, USA

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Re: Are dcachesize values supposed to be 0's? [message #27105 is a reply to message #27059]

Sat, 09 February 2008 19:54

maratrus
Messages: 1495
Registered: August 2007
Location: Moscow

Senior Member

Hi,

I suppose it is a normal behavior.
To decrease the overhead concerned with dcache accounting the following policy are used. There are two values which are responsible of dcache accounting. If dentry_cache size exceeded the first value the accouting is switched on and it becomes on until dentry_cache becomes smaller than the second value.

sysctl parameter ubc.dentry_watermark helps us to manage a dcache accounting.

ubc.dentry_watermark = 0 100 means that accounting is switched on if dcache size exceeded 10% of memory and switched off if it will take 0%.

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