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Description
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On my Thinkpad with 4Gb of memory, if I start three domains
(two 1Gb, one of which is HVM, one 512Mb), then the machine becomes barely usable.
It's evidently running out of memory. Tuning down zfs_arc_max
to 256Mb helps enormously (it's still not perfect whilst
things are booting, but it's interactively usable and remains
so).
Presumably the ballooning down of dom0 is screwing up what
the ZFS ARC expects to happen, as we take a huge chunk of
memory out of action and never give it back, but never tell ZFS
what we've done (and it does seem to want to know).
Re-assigning to ZFS after Stu Maybee suggested I get
a crash dump. Whilst I originally
reproduced this on my laptop, I've used a lab
machine for generating the dump. I did:
xm mem-set 0 1400
(the equivalent of starting several domUs on the machine)
to give:
[1]> ::memstat
Page Summary Pages MB %Tot
------------ ---------------- ---------------- ----
Kernel 823493 3216 43%
Anon 861 3 0%
Exec and libs 532 2 0%
Page cache 83 0 0%
Free (cachelist) 984 3 0%
Free (freelist) 57102 223 3%
Balloon 1031394 4028 54%
Total 1914449 7478
and the machine becomes nearly unusable:
killerbee:/ # ls /
bash: fork: Resource temporarily unavailable
On my laptop, limiting zfs_arc_max to 256Mb fixed the problem.
Crash dump is at /net/mdb.eng/cores/johnlev/6647989
> ::arc ! grep size
size = 796 MB
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