Package: procps
Version: 1:3.2.8-2
Severity: important
Tags: patch
Due to a very old bug in vmstat (apparently wrong descision), vmstat
always displays zero in swap in/out columns when invoked with -SM
(units=Mb). This is because in that case, si/so gets converted to
megabytes/sec (or tried to, anyway), which is insane swap levels.
On the other hand, using -SM on nowadays machines makes much more
sense because amount of memory on a typical machine is measured in
gigabytes, thus making default vmstat display hardly readable.
Note also that bi/bo columns (I/O per sec) is not affected by -S.
The patch attached just removes wrong unit conversion for kb_per_page
to megabytes (!), making the whole thing more sensible.
Severity is important because vmstat is one of essential tools to
diagnose system problems (including inadequate memory usage), and
it is assumed the tool is correct, but since it displays 0 for
swapping such important problem gets unnoticed. As far as I can
see, many people hit this trap - not noticing the swapping while
the sole reason for their system slowness is swapping.
Thanks!
-- System Information:
Debian Release: 5.0.3
APT prefers stable
APT policy: (990, 'stable'), (60, 'testing'), (50, 'unstable'), (1,
'experimental')
Architecture: i386 (x86_64)
Kernel: Linux 2.6.32-rc7-amd64 (SMP w/2 CPU cores)
Locale: LANG=ru_RU.UTF-8, LC_CTYPE=ru_RU.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Versions of packages procps depends on:
ii initscripts 2.86.ds1-61 Scripts for initializing and shutt
ii libc6 2.7-18 GNU C Library: Shared libraries
ii libncurses5 5.7+20081213-1 shared libraries for terminal hand
ii lsb-base 3.2-20 Linux Standard Base 3.2 init scrip
Versions of packages procps recommends:
ii psmisc 22.6-1 Utilities that use the proc filesy
procps suggests no packages.
-- no debconf information
Fix vmstat swap (si/so) displaying to be != 0
by default vmstat displays statistics in Kb. There's a command-line
switch, -S, to specify units - either Kb or Mb. With -SM (Mb), some
stats gets converted to megabytes - such as amount of memory and swap.
But for some values such conversion makes no good sense. For example,
block i/o (bi&bo) are always displayed in Kb/sec regardless of -S,
because it is not yet expected to see disk speeds in gigabytes per
sec. But swapin/swapout (si&so columns) gets converted to megabytes
per sec, and if we're reaching this level of swap the system is barely
usable. It is not a good idea to convert si&so to megabytes.
It's more: the usage of
swaps * unitConvert(kb_per_page)
is already wrong. unitConvert converst the value to either kb or mb,
and kb_per_page is usually a small number like 4. Converting it to
mb will return 0. So swap will always be 0 if we're converting to
megabytes.
In short, with -SM swap as displayed by vmstat is always 0.
But -SM makes much more sense nowadays because amount of memory on
a typical system measured in gigabytes, so that vmstat memory area
gets large and other colums are shifted.
The fix is to remove the unitConvert() call for swap stats to always
display swap in/out values in kb/sec, as done with block i/o (bi/bo).
This is a very old issue, but it's also a classical trap: when looking
at vmstat output while debugging "slow system" issue, it is vital to
have correct information in swap in/out columns. Or else, in case of
swapping, such swapping wont be noticed.
Signed-off-by: Michael Tokarev <m...@tls.msk.ru>
--- procps-3.2.8/vmstat.c.orig 2009-11-26 12:44:33.217326167 +0300
+++ procps-3.2.8/vmstat.c 2009-11-26 12:43:46.670940161 +0300
@@ -211,4 +211,4 @@
unitConvert(a_option?kb_active:kb_main_cached),
- (unsigned)( (*pswpin * unitConvert(kb_per_page) * hz + divo2) / Div ),
- (unsigned)( (*pswpout * unitConvert(kb_per_page) * hz + divo2) / Div ),
+ (unsigned)( (*pswpin * kb_per_page * hz + divo2) / Div ),
+ (unsigned)( (*pswpout * kb_per_page * hz + divo2) / Div ),
(unsigned)( (*pgpgin * hz + divo2) / Div ),
@@ -260,4 +260,4 @@
unitConvert(a_option?kb_active:kb_main_cached),
- (unsigned)( ( (pswpin [tog] - pswpin
[!tog])*unitConvert(kb_per_page)+sleep_half )/sleep_time ), /*si*/
- (unsigned)( ( (pswpout[tog] -
pswpout[!tog])*unitConvert(kb_per_page)+sleep_half )/sleep_time ), /*so*/
+ (unsigned)( ( (pswpin [tog] - pswpin [!tog])*kb_per_page+sleep_half
)/sleep_time ), /*si*/
+ (unsigned)( ( (pswpout[tog] - pswpout[!tog])*kb_per_page+sleep_half
)/sleep_time ), /*so*/
(unsigned)( ( pgpgin [tog] - pgpgin [!tog] +sleep_half
)/sleep_time ), /*bi*/
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