Re: [gentoo-user] mysqld invoked oom-killer

[Paul Hartman]

On Thu, Jul 21, 2011 at 8:29 PM, Grant <emailgrant@×××××.com> wrote:
>>> Its more how much i/o rather than the size. If you have a bunch of
>>> stuff swapped out, but it hardly ever needs to be swapped in, the
>>> impact will be low.
>>>
>>> Keep an eye on the use with vmstat;
>>>
>>> adam@rix ~ $ vmstat 5
>>> procs -----------memory---------- ---swap-- -----io---- -system--
>>> ----cpu----
>>>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us
>>> sy id wa
>>>  0  0  56700 351244  79564 207848    0    0     3     3   11    7  1
>>> 0 99  0
>>>  0  0  56700 351244  79564 207848    0    0     0     8   52   27  0
>>> 0 100  0
>>>  0  0  56700 351244  79564 207848    0    0     0     0   45   14  0
>>> 0 100  0
>>>  0  0  56700 351244  79564 207848    0    0     0     0   47   17  0
>>> 0 100  0
>>>
>>> from the man page;
>>>    Swap
>>>        si: Amount of memory swapped in from disk (/s).
>>>        so: Amount of memory swapped to disk (/s).
>>>
>>>
>> Exactly!  My system is the same way.
>>
>> Right now I've got a 4GB system that's using 708MB swap.  But vmstat
>> isn't showing any swap activity.  Why?  Because some processes that I'm
>> not aware about because I'm obviously not using, got swapped out a long
>> time ago, and Linux is using that reclaimed RAM to compile chromium ;)
>>
>> If/when I need part of that 708MB becomes active, Linux will swap it
>> back in in one short burst that I doubt that I'll even notice.
>
> Then why not have a really big swap file?  If swap is useful as a
> second layer of caching behind RAM, why doesn't everyone with some
> extra hard drive space have a 100GB swap file?

I have 12GB of RAM and 12GB of swap on my main PC. Why? Because... why
not? :) After 5 days uptime, it actually has 89M of swap used for some
reason. It has over 10GB cached. All of my sysctl vm.* settings have
been left to the defaults. So I guess it just pushed some unused stuff
out to swap to make room for more caching.