How to free used Swap-Space?

[Peter]

On Tue, Sep 22, 2020 at 12:33:19PM -0400, Mark Johnston wrote:

! On Tue, Sep 22, 2020 at 06:08:01PM +0200, Peter wrote:

! >  my machine should use about 3-4, maybe 5 GB swapspace. Today I found
! > it suddenly uses 8 GB (which is worryingly near the configured 10G).
! > 
! > I stopped all the big suckers - nothing found.
! > I stopped all the jails - no success.
! > I brought it down to singleuser: it tried to swapoff, but failed.
! > 
! > I unmounted all filesystems, exported all pools, detached all geli,
! > and removed most of the netgraphs. Swap is still occupied.
! > ! > Machine is now running only the init and a shell processes, has
! > almost no filesystems mounted, has mostly native networks only, and
! > this still occupies 3 GB of swap which cannot be released.
! > 
! > What is going on, what is doing this, and how can I get this swapspace
! > released??
! 
! Do you have any shared memory segments lingering?  ipcs -a will show
! SysV shared memory usage.

I have four small shmem segments from four postgres clusters running.
These should cleanly disappear when the clusters are stopped, and
they are very small.

Shared Memory:
T           ID          KEY MODE        OWNER    GROUP    CREATOR  CGROUP         NATTCH        SEGSZ         CPID         LPID ATIME    DTIME    CTIME   
m        65536      5432001 --rw------- postgres postgres postgres postgres            7           48         4793         4793  6:09:34 18:00:31  6:09:34
m        65537            0 --rw------- postgres postgres postgres postgres           11           48         6268         6268  6:09:42 10:48:27  6:09:42
m        65538            0 --rw------- postgres postgres postgres postgres            5           48         6968         6968  6:09:46 18:28:36  6:09:46
m        65539            0 --rw------- postgres postgres postgres postgres            6           48         6992         6992  6:09:47  3:38:34  6:09:47

! For POSIX shared memory, in 11.4 we do not
! have any good way of listing objects, but "vmstat -m | grep shmfd" will
! at least show whether any are allocated.

There is something, and I don't know who owns that:
$ vmstat -m | grep shmfd
        shmfd    13    14K       -      473  64,256,1024,8192

But that doesn't look big either.

Furthermore, this machine is running for quite some time already; it
was running as i386 (with ZFS) until very recently, and I know quite
well what is using much memory: these 3 GB were illegitimate; they
came from nothing I did install. And they are new; this has not
happened before.

! If those don't turn anything
! up then it's possible that there's a swap leak.  Do you use any DRM
! graphics drivers on this system?

Probably yes. There is no graphics used at all; it just uses "device
vt" in text mode, but it uses i5-3570T CPU (IvyBridge HD2500) graphics
for that, and the driver is "drm2" and "i915drm" from /usr/src/sys (not
those from ports).
Not sure how that would account for 3 GB, unless there is indeed some
leak.

regards,
PMc