is TMPFS still highly experimental?

[Olivier Smedts]

2011/10/5 Gleb Kurtsou <gleb.kurtsou at gmail.com>:
> Free RAM is a bit tricky with virtual memory and overcommit support all
> over the place. There are at least 3 memory hungry subsystems: buffer
> cache, ZFS ARC, tmpfs.
>
> For the first two there is defined maximum size and they can be shrunk
> in low memory situations. Tmpfs grows as much as it can trying to
> calculate "free" memory available. Another difference is that tmpfs
> can't be shrunk in low memory situation.
>
> I proposed a patch changing tmpfs memory allocation:
> - Define maximum file system size (RAM/2 by default)
> - Don't try to check if free memory available, check free swap
>  instead and allocate more aggressively, i.e. allocate until
>  swap or file system limit is reached.

Patch tested and approved ! I did not test the maximum tmpfs default
size because I allocated a max size in my fstab.

%cat /etc/fstab
none /tmp tmpfs rw,mode=1777,size=2147483648 0 0

%df -h /tmp
Filesystem    Size    Used   Avail Capacity  Mounted on
tmpfs         2.0G    124k      2G     0%    /tmp

Mem: 622M Active, 351M Inact, 6491M Wired, 4940K Cache, 2160K Buf, 385M Free
Swap: 2048M Total, 36M Used, 2012M Free, 1% Inuse

(ZFS is using all my wired memory, the ARC is now full, and I deleted
my nearly-never-touched 8G swap in favor of a 2G swap)

A little test now :
%dd if=/dev/zero of=/tmp/test bs=1M count=1500
1500+0 records in
1500+0 records out
1572864000 bytes transferred in 0.763368 secs (2060427243 bytes/sec)
%df -h /tmp
Filesystem    Size    Used   Avail Capacity  Mounted on
tmpfs         2.0G    1.5G    542M    74%    /tmp
% top
Mem: 2559M Active, 514M Inact, 4506M Wired, 1656K Cache, 2160K Buf, 274M Free
Swap: 2048M Total, 39M Used, 2009M Free, 1% Inuse

So tmpfs made the ZFS ARC cache shrink, without swapping. I did not
test filling my active memory to see if the max tmpfs size was
shrinking.

Cheers !

>
> Patch:
> http://marc.info/?l=freebsd-fs&m=129747367322954&w=2
> https://github.com/glk/freebsd-head/tree/tmpfs
>
> Thanks,
> Gleb.
>


-- 
Olivier Smedts                                                 _
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