[CentOS-virt] Pages In and Read Sectors in Guest Domain

Sun Apr 6 16:18:27 UTC 2014
Deron <fecastle at gmail.com>


I have been doing some performance tests with Xen and CentOS and have found
some strange statistics when comparing the virtual memory (/proc/vmstat)
and I/O (/proc/diskstat) statistics between the Domain 0 and guests.

When I look at the "pgpgin" statistic it is exactly the same as the "read
sectors" in Dom0.  However, when I look at the same statistics in the
guest, the "read sectors" is exactly 2x "pgpgin".

I have tried this on 2 different versions, each on a different physical
server. Here is an example of the statistics over a 30 second period (while
running a benchmark in Dom1) in the Dom0 and Guest Domain.
                       pgpgin       read sectors
                       =======     =========
      Dom0        1698024     1698024
      Dom1          848412     1696824

I have looked at some various settings to see if I could explain it.  I
can't tell if the Dom1 guest kernel is reporting incorrectly, or there is
some other explanation.  If anyone has any ideas about this I would
appreciate any feedback.

Dom 0 kernels

Guest kernel


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