tmpfs out of space (ZFS related?)

[Gleb Kurtsou]

On (21/11/2010 22:22), Ivan Voras wrote:
> I got a curious error today while starting PostgreSQL, complaining about 
> "out of space" errno while creating lock file on /tmp.
> 
> /tmp on this machine is mounted as tmpfs and indeed, here is the statistic:
> 
> biggie:/# df -i
> Filesystem    1M-blocks  Used  Avail Capacity iused     ifree %iused 
> Mounted on
> /dev/mfid0s1a      9912  5193   3926    57%  306079   1012831   23%   /
> devfs                 0     0      0   100%       0         0  100%   /dev
> fdescfs               0     0      0   100%       4     11092    0% 
> /dev/fd
> tmpfs                 0     0      0   100%       9         0  100%   /tmp
> tank             376044     0 376044     0%       4 770138347    0%   /tank
> tank/ports       376658   614 376044     0%  145919 770138347    0% 
> /usr/ports
> tank/mysql       376073    29 376044     0%     102 770138347    0% 
> /var/db/mysql
> tank/pgdata90    400469 24425 376044     6%    1047 770138347    0% 
> /tank/pgdata90
> 
> On the other hand, "top" reports this:
> 
> last pid: 79667;  load averages:  0.08,  0.68,  0.77    up 1+09:12:13 
> 00:11:33
> 44 processes:  1 running, 43 sleeping
> CPU:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
> Mem: 13M Active, 46M Inact, 15G Wired, 232K Cache, 1458M Buf, 8358M Free
> Swap: 1024M Total, 1024M Free
> 
> Note the "8358M free" report.
That's probably integer overflow, could you try specifying max
size as mount option. There was a series of integer overflows in tmpfs.
Used and available are 0 in df output. On my system I have:
% df
Filesystem         Size    Used   Avail Capacity  Mounted on
tmpfs              4.3G    4.0K    4.3G     0%    /usr/obj/ports

Also note, that tmpfs does somewhat weired thing on constantly
recalculating available space based on free memory/swap (not sure if
specifying max size would fix it).

Did you try double copy elimination patch by kib@?
http://lists.freebsd.org/pipermail/freebsd-fs/2010-June/008786.html

It doesn't apply cleanly to current any more, but fixing it shouldn't be
hard. The patch wouldn't fix this particular issue but looks very
promising.

Thanks,
Gleb

> The server has ZFS and was doing IO intensive database work on it; the 8 
> GB free memory comes from PostgreSQL being restarted and freeing the 
> memory (but failing to start again...).
> 
> Starting PostgreSQL gets me this message:
> Nov 22 00:18:24 biggie postgres[79696]: [1-1] FATAL:  could not write 
> lock file "/tmp/.s.PGSQL.5432.lock": No space left on device
> 
> This is 8-STABLE amd64.
> 
> Running "touch /tmp/abc" works, and creates a file. Running "echo abc > 
> /tmp/abc" doesn't return an error but *doesn't write anything to the 
> file*, just creates a directory entry.
> 
> The status doesn't change over time, i.e. "df" on tmpfs always shows "0 
> free".
> 
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