2012-10-22 18:24, Daniel Kjar wrote:
I have this problem with any VM running on either Sol10 Nevada, Opensolaris, openindiana. I have the ARC restricted now but for some reason, and 'people at sun that know these things' have mentioned it before when sun still existed, when something needs a big devoted chunk of ram, zfs fails miserably at giving up its cache. If I don't limit the ARC, a few days of even a single VM running causes the system to start stalling. With the ARC limit, everything is peaches.
I think limiting the ARC was the recommended practice for VirtualBox in either ZFS Evil Tuning Guide or VirtualBox manuals, or both. Also remember that VBox requires disk-based swap to be available at the time of start of VMs in amounts comparable to VMs' RAM size, so that if needed, these processes can be guaranteed to be able to swap. On a different note, there are programs which check system available memory and fail themselves if there's not enough - without asking the OS to give them some memory. In this case ARC gets no signals to shrink because some process needs the RAM. Rule of thumb for admins was to estimate or measure the "stable" RAM requirements of running processes, add 1GB for good measure, and limit ARC to the rest. As for lags and failures in relation to ARC, I'd guess that getting and releasing RAM in vast amounts and small chunks would fragment the memory, possibly to the extent that while the needed total free RAM is available, no contiguous block can be allocated of the size needed by a process (or that there's too much random access and virtual memory mapping involved, requiring much CPU for each memory access from userland processes). But that's just an educated guess. HTH, //Jim _______________________________________________ OpenIndiana-discuss mailing list [email protected] http://openindiana.org/mailman/listinfo/openindiana-discuss
