Page-faults by a process on writing OR reading are really not that different. In both cases, an attempt is made to read the physical address (corresponding to the virtual address) from the page-table BEFORE the read or write machine level instructions are executed. So, if the address to which writes (or reads) are being performed, does not have a valid page-table entry ie. a valid virtual address, a page-fault will be triggered.
Best Regards
Gaurav Jain
On Fri, Apr 19, 2013 at 11:42 PM, Daniel Hilst Selli <danielhilst@xxxxxxxxx> wrote:
My case is this, I'm using collectd [1] with rrdtool [2] to monitor some
server.
a) When I enable rrdtool plugin I can grab collectd process as top page
fault process on top command.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ nFLT COMMAND
20128 root 18 0 4105m 35m 17m S 7.9 0.3 0:09.62 22k
/opt/collectd/sbin/collectd
b) Disabling rrdtool plugin dramastically decrease the number of page
faults of collectd.
c) I know that rrdtool plugin is known to generate a lot of small
writes, as stated in [3]. Also I know the parameters to improving
collectd's cache usage to save I/O, but this is not the question here..
AFAIK, major page faults are generated when data that is not yet present
on RAM is loaded from disk, but in this case data is being write do
disk, I can't
see how writes can generate faults, but still, it seems that is
happening, ... !?
Is that possible?
Cheers,
[1] http://www.collectd.org
[2] http://oss.oetiker.ch/rrdtool/
[3] https://collectd.org/wiki/index.php/Inside_the_RRDtool_plugin
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Gaurav Jain
Associate Software Engineer
VxVM Escalations Team, SAMG
Symantec Software India Pvt. Ltd.
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