Difference between revisions of "IO accounting"
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| − | This page describes how | + | This page describes how I/O activity of VE processes is accounted. This feature is available since OpenVZ kernels version <code>028test008</code>. |
== New resources == | == New resources == | ||
The following resources are accounted: | The following resources are accounted: | ||
; read bytes | ; read bytes | ||
| − | : is the amount of bytes read by tasks. Reads are always synchronous in kernel so this type of resources is the easiest one | + | : 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 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: | + | : 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 page is mapped it's "mapper" is used as this may happen in any context (unmapping of 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 page is not mapped | + | :* 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 amount of bytes flushed to disk. The beancounter to charge this to is the one the page was dirtied by | + | : 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 amount of bytes that were dirty but weren't flushed to disk | + | : is the amount of bytes that were dirty but weren't flushed to disk. |
; missed bytes | ; missed bytes | ||
| − | : is the amount of bytes that were dirtied but the context (beancounter) wasn't saved due to lack of memory | + | : is the amount of bytes that were dirtied but the context (beancounter) wasn't saved due to lack of memory. |
== Proc interface == | == Proc interface == | ||
=== General information === | === General information === | ||
| − | As it was described in [[BC proc entries|another artice]] each beancounter has it's own <code>/proc/bc/$BCID</code> directory where subsystems add their entries. | + | As it was described in [[BC proc entries|another artice]] each beancounter has it's own <code>/proc/bc/$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 33: | Line 33: | ||
</pre> | </pre> | ||
| − | Note that <code>dirty</code> is not the size of dirty data at the moment but | + | 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 in system. | + | 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 49: | Line 49: | ||
== Auxiliary information == | == Auxiliary information == | ||
| − | Along with VFS | + | Along with VFS I/O activity the following information is gathered |
; sync counts | ; sync counts | ||
| − | : The number of <code>sync(2)</code>, <code>fsync(2)</code>, <code>fdatasync(2)</code> and <code>sync_file_range</code> | + | : The number of <code>sync(2)</code>, <code>fsync(2)</code>, <code>fdatasync(2)</code> and <code>sync_file_range</code>. |
<pre> | <pre> | ||
# cat /proc/bc/101/ioacct | # cat /proc/bc/101/ioacct | ||
| Line 67: | Line 67: | ||
; write/read calls counts | ; write/read calls counts | ||
| − | : | + | : The number of <code>read(2)</code>, <code>readv(2)</code>, <code>write(2)</code>, <code>writev(2)</code>, etc. and the number of bytes passed. |
<pre> | <pre> | ||
# cat /proc/bc/101/ioacct | # cat /proc/bc/101/ioacct | ||
| Line 77: | Line 77: | ||
</pre> | </pre> | ||
| − | ; number of page beancounters pinned by | + | ; number of page beancounters pinned by I/O |
: This is the number of page beancounters that save information about page dirtier. This is actually the number of dirty pages within beancounter at the moment. | : This is the number of page beancounters that save information about page dirtier. This is actually the number of dirty pages within beancounter at the moment. | ||
<pre> | <pre> | ||
Revision as of 15:34, 27 December 2006
This page describes how I/O activity of VE processes is accounted. This feature is available since OpenVZ kernels version 028test008.
Contents
New resources
The following resources are accounted:
- read bytes
- 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
- 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 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 not mapped — current BC is used as this can happen during usual write (writev) only.
- written bytes
- is the amount of bytes flushed to disk. The beancounter to charge this to is the one the page was dirtied by.
- canceled bytes
- is the amount of bytes that were dirty but weren't flushed to disk.
- missed bytes
- is the amount of bytes that were dirtied but the context (beancounter) wasn't saved due to lack of memory.
Proc interface
General information
As it was described in another artice each beancounter has it's own /proc/bc/$BCID directory where subsystems add their entries. I/O accounting adds ioacct entry to show I/O information. This entry contains the following information:
# cat /proc/bc/101/ioacct
read 24330240
write 598016
dirty 622592
cancel 24576
missed 0
...
Note that dirty is not the size of a dirty data at the moment, but the size of a dirty data seen so far.
Debugging information
When CONFIG_UBC_DEBUG_IO, is on /proc/bc/ioacct_debug is added. This entry contains a snapshot of current dirty pages with its beancounter in system. For example:
# cat /proc/bc/ioacct_debug Races: io 0 anon 0 clean 0 missed 0 pb page flg cnt mcnt pb_list page_pb mapping ub f7a4a520 e c17cfc68 Dawl 2 0 00000000 f7a4a521 c3870168 0 f7a15ce0 e c17d034c Dawl 2 0 00000000 f7a15ce1 c3870168 0 f72e4680 e c1083364 Dawl 2 0 00000000 f72e4681 c3870168 0 f72e4800 e c1083388 Dawl 2 0 00000000 f72e4801 c3870168 0 f7a15dc0 e c17d0010 Dawl 2 0 00000000 f7a15dc1 c3870168 0
Auxiliary information
Along with VFS I/O activity the following information is gathered
- sync counts
- The number of
sync(2),fsync(2),fdatasync(2)andsync_file_range.
# cat /proc/bc/101/ioacct
...
syncs_total 0
fsyncs_total 0
fdatasyncs_total 10
range_syncs_total 0
syncs_active 0
fsyncs_active 0
fdatasyncs_active 0
range_syncs_active 0
_active suffix refers to the number of operations in progress.
- write/read calls counts
- The number of
read(2),readv(2),write(2),writev(2), etc. and the number of bytes passed.
# cat /proc/bc/101/ioacct
...
vfs_reads 24491
vfs_read_chars 2616512
vfs_writes 380
vfs_write_chars 30064899102
- number of page beancounters pinned by I/O
- This is the number of page beancounters that save information about page dirtier. This is actually the number of dirty pages within beancounter at the moment.
# cat /proc/bc/0/ioacct
...
write 598016
dirty 622592
...
io_pbs 0
# dd if=/dev/zero of=tmp bs=512 count=40
# cat /proc/bc/0/ioacct
...
write 598016
dirty 643072
...
io_pbs 5
# sync
# cat /proc/bc/0/ioacct
...
write 618496
dirty 643072
...
io_pbs 0
