How to free used Swap-Space? (from errno=8)

Tue Sep 22 22:54:25 UTC 2020

On Wed, Sep 23, 2020 at 12:03:32AM +0300, Konstantin Belousov wrote:
! On Tue, Sep 22, 2020 at 09:11:49PM +0200, Peter wrote:
! > So what happens then is this:
! > 
! > $ file scc.e
! > scc.e: ELF 32-bit LSB executable, Intel 80386, version 1
! > (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1,
! > for FreeBSD 9.3 (903504), stripped
! > 
! > $ ./scc.e
! > ELF interpreter /libexec/ld-elf.so.1 not found, error 8
! > Abort trap
! > 
! > And this will cost about some (hundred?) kB of swapspace every time it
! > happens. And they do not go away again, neither can the concerned jail
! > do fully die again.
! In what sense it 'costs' ?

Well that amount memory gets occupied. Forever, that is, until
poweroff/reset.

! Can you show exact sequence of commands and outputs that demostrate your
! point ?  What type of filesystem the binaries live on ?

Oh, I didn't care. Originally on ZFS. When I tried to reproduce it,
most likely on an NFS-4 share, as I didn't bother to put it anywhere
special.

! I want to reproduce it locally.

Yes that's great! Lets see which info You are lacking.
Here we are now on my desktop box (mostly same machine, same
configuration, i5-3570, 11.4-p3, amd64).

I explicitely removed all the files that do not get installed
when /etc/src.conf contains the "WITHOUT_LIB32=", but I have the
COMPAT_FREEBSD32 still in the kernel.

Now I fetch such an old R9.3/i386 binary from my backups, and
drop it into some NFS filesystem:
(That binary is only 4kB, I just attach it here, if you wanna try
you can straightaway use that one - in normal operation it just
converts some words stdin to stdout).

admin at disp:510:1/ext/Repos$ dir usr2sys
-rwxr-xr-x   1 bin       bin    4316 Apr  7  2016 usr2sys
admin at disp:511:1/ext/Repos$ file usr2sys 
usr2sys: ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 9.3 (903504), stripped
admin at disp:513:1/ext/Repos$ mount | grep Repos
edge-e:/ext/Repos on /ext/Repos (nfs, nfsv4acls)
admin at disp:514:1/ext/Repos$ top | cat
Mem: 952M Active, 1687M Inact, 419M Laundry, 4423M Wired, 774M Buf, 348M Free
ARC: 1940M Total, 1378M MFU, 172M MRU, 2492K Anon, 48M Header, 340M Other
     1134M Compressed, 2749M Uncompressed, 2.43:1 Ratio
Swap: 20G Total, 36M Used, 20G Free

As we see, this machine has 8 Gig installed and currently about no swap
used. Now watch what happens:
epos$ ./usr2sys 
ELF interpreter /libexec/ld-elf.so.1 not found, error 8
Abort trap

admin at disp:519:1/ext/Repos$ for i in `seq 1000`
> do ./usr2sys
> done
ELF interpreter /libexec/ld-elf.so.1 not found, error 8
Abort trap
...

admin at disp:514:1/ext/Repos$ top | cat
Mem: 1010M Active, 1807M Inact, 419M Laundry, 4523M Wired, 774M Buf, 69M Free
ARC: 1940M Total, 1383M MFU, 166M MRU, 2503K Anon, 48M Header, 340M Other
     1134M Compressed, 2750M Uncompressed, 2.43:1 Ratio
Swap: 20G Total, 36M Used, 20G Free

The free memory has already disappeared!

admin at disp:521:1/ext/Repos$ for i in `seq 5000`; do ./usr2sys ; done
...

admin at disp:522:1/ext/Repos$ top | cat
Mem: 2154M Active, 78M Inact, 787M Laundry, 4722M Wired, 774M Buf, 89M Free
ARC: 1753M Total, 1273M MFU, 97M MRU, 2653K Anon, 39M Header, 340M Other
     953M Compressed, 2445M Uncompressed, 2.56:1 Ratio
Swap: 20G Total, 358M Used, 20G Free, 1% Inuse

Now the swapspace starts filling.
Lets see if the placement filesystem makes any difference and go onto UFS:

admin at disp:525:1/ext/Repos$ su -
Password:
root at disp:~ # cp /ext/Repos/usr2sys /var
root at disp:~ # dir /var/usr2sys 
-rwxr-xr-x  1 bin  bin  4316 Sep 22 23:55 /var/usr2sys
root at disp:~ # mount | grep /var
/dev/ada0p5 on /var (ufs, local, soft-updates)

admin at disp:527:1/var$ ./usr2sys 
ELF interpreter /libexec/ld-elf.so.1 not found, error 8
Abort trap

admin at disp:521:1/ext/Repos$ for i in `seq 5000`; do ./usr2sys ; done
ELF interpreter /libexec/ld-elf.so.1 not found, error 8
Abort trap
...

Ahh, that runs a LOT faster now than on the NFS!

admin at disp:529:1/var$ top | cat
Mem: 1546M Active, 67M Inact, 934M Laundry, 5121M Wired, 774M Buf, 161M Free
ARC: 1646M Total, 1159M MFU, 107M MRU, 2686K Anon, 37M Header, 340M Other
     849M Compressed, 2257M Uncompressed, 2.66:1 Ratio
Swap: 20G Total, 1658M Used, 18G Free, 8% Inuse

But memory leakage is similar to worse.

admin at disp:530:1/var$ df tmp
Filesystem    1K-blocks   Used    Avail Capacity  Mounted on
zdesk/var/tmp  24747504 231052 24516452     1%    /var/tmp
admin at disp:531:1/var$ cp usr2sys tmp
admin at disp:532:1/var$ cd tmp
admin at disp:533:1/var/tmp$ ./usr2sys 
ELF interpreter /libexec/ld-elf.so.1 not found, error 8
Abort trap
admin at disp:534:1/var/tmp$ for i in `seq 5000`; do ./usr2sys ; done
...

You can see this is now a ZFS, and the behaviour is basically the same:

Mem: 1497M Active, 5292K Inact, 803M Laundry, 5313M Wired, 774M Buf, 212M Free
ARC: 1432M Total, 963M MFU, 105M MRU, 2511K Anon, 21M Header, 341M Other
     650M Compressed, 1482M Uncompressed, 2.28:1 Ratio
Swap: 20G Total, 2791M Used, 17G Free, 13% Inuse

Now we have 3 gig eaten up, so we loose approx. 1 gig per 5000
aborted invocations.

And these do not go get freed anymore. One could continue this now, and
probably at some point the system will crash (and probably, beforehand
it will do some OOM killing), but I don't want to try that out now,
I'll just reboot now.

regards,
PMc
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