Swap Usage

Peter Jeremy peter at rulingia.com
Thu Jul 30 06:51:04 UTC 2015


On 2015-Jul-29 17:41:33 -0700, Doug Hardie <bc979 at lafn.org> wrote:
>I have several FreeBSD 9.3 systems that are using swap and I can’t
>figure out what is doing it.  The key system has 6GB swap and
>currently it has over 2GB in use.

Is the system currently paging (top(1) and "systat -v" will show
this)?  If not, this just means that at some time in the past, the
system was under memory pressure and paged some process memory out.
Since then, that memory hasn't been touched so the system hasn't paged
it in.

>ps shows only a kernel module
>[intr] with a W status.

'W' means the whole process is 'swapped' out - this will only occur
under severe RAM pressure.  Normally, the system will just page out
inactive parts of a processes address space - and none of the ps flags
will show this.

>  How do I figure out what that swap space is being used for?

I don't think this can be trivially done.  "procstat -v" will show
the number of resident pages within each swap-backed region, any
pages in that region that have been touched but are not resident
are on the swap device but any pages that have never been touched
aren't counted at all.

Peter Jeremy
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