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− | This page describes accounting for I/O activity of | + | This page describes how accounting is done for I/O activity of VE processes. This feature is available beginning with OpenVZ kernels version <code>028test008</code>. |
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== New resources == | == New resources == | ||
The following resources are accounted: | The following resources are accounted: | ||
; read bytes | ; read bytes | ||
− | : is the | + | : is the amount of bytes read by tasks. Reads are always synchronous in kernel so this type of resources is the easiest one. |
; dirty bytes | ; dirty bytes | ||
− | : is the | + | : is the amount of bytes that were dirty since VE start, i. e. data that isn't yet flushed to disk. This type of resources is accounted using [[RSS_fractions_accounting|page beancounters]] and the context the page was dirtied by is determined like this: |
:* if a page is mapped it's "mapper" is used as this may happen in any context (unmapping of a page under memory pressure); | :* if a page is mapped it's "mapper" is used as this may happen in any context (unmapping of a page under memory pressure); | ||
:* if a page is not mapped — current BC is used as this can happen during usual write (writev) only. | :* if a page is not mapped — current BC is used as this can happen during usual write (writev) only. | ||
; written bytes | ; written bytes | ||
− | : is the | + | : is the amount of bytes flushed to disk. The beancounter to charge this to is the one the page was dirtied by. |
; canceled bytes | ; canceled bytes | ||
− | : is the | + | : is the amount of bytes that were dirty but weren't flushed to disk. |
; missed bytes | ; missed bytes | ||
− | : is the | + | : is the amount of bytes that were dirtied but the context (beancounter) wasn't saved due to lack of memory. |
== Proc interface == | == Proc interface == | ||
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=== General information === | === General information === | ||
− | As was described in [[BC proc entries|another article]] each beancounter has | + | As it was described in [[BC proc entries|another article]] each beancounter has it's own <code>/proc/bc/$BCID</code> directory where subsystems add their entries. I/O accounting adds <code>ioacct</code> entry to show I/O information. This entry contains the following information: |
<pre> | <pre> | ||
# cat /proc/bc/101/ioacct | # cat /proc/bc/101/ioacct | ||
Line 39: | Line 33: | ||
</pre> | </pre> | ||
− | Note that <code>dirty</code> is not the size of dirty data at the moment, but the size of dirty data seen so far. | + | 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. |
=== Debugging information === | === Debugging information === | ||
− | 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. For example: | + | 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: |
<pre> | <pre> | ||
# cat /proc/bc/ioacct_debug | # cat /proc/bc/ioacct_debug | ||
Line 107: | Line 101: | ||
io_pbs 0 | io_pbs 0 | ||
</pre> | </pre> | ||
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[[Category:Resource management]] | [[Category:Resource management]] |