Changes

This page describes how accounting for I/O activity of VE CT processes is accounted, on a VFS I/O level. This The feature is available since beginning with OpenVZ kernels version <code>028test008</code>. If you are interested in [[I/O priorities for containers]], it is described in a separate article. If you are looking for IO scheduler (i.e. lower level) statistics, see [[IO statistics]] instead.

: is the amount number of bytes read by tasks. Reads are always synchronous in the kernel so this type of resources resource is the easiest one.

: is the amount number of bytes that were dirty since VE start, i.&nbsp;e. data that isn't yet flushed to disk. This type of resources resource is accounted accumulated using [[RSS_fractions_accounting|page beancounters]] and the context the page was dirtied by is determined like this:

: is the amount number of bytes flushed to disk. The beancounter to charge charged with this to is the one by which the page was dirtied by.

: is the amount number of bytes that were dirty but weren't flushed to disk.

: is the amount number of bytes that were dirtied but the context (beancounter) wasn't saved due to lack of memory.

As it was described in [[BC proc entries|another article]] each beancounter has it's its own <code>/proc/bc/$BCID</code> directory where subsystems add their entries. I/O accounting adds an <code>ioacct</code> entry to show I/O information. This entry contains the following information:

Note that <code>dirty</code> is not the size of a dirty data at the moment, but the size of a dirty data seen so far.

When <code>CONFIG_UBC_DEBUG_IO</code>, is on <code>/proc/bc/ioacct_debug</code> is added. This entry contains a snapshot of current dirty pages with its beancounter in system. For example: