David & Richard, Thanks for continuing on the discussion under a new topic. I suppose the discussion board software had a little too much to drink last night ;-)
First of all - David I am not the Sean from SSHA, but I am in Toronto. I'll send you a note shortly to have a discussion some time :-) I can see you actually do understand my points, and the history of issue, that's good. And yes I hate to be reactive and just wait for scan rate to tell me that I am out of memory. Richard, Before Solaris 8, vmstat freemem only shows freelist, so after UFS cache took all of the free memory, freelist will eventually shrink to minfree. And that's the behavior you talked about. However with Solaris 8, vmstat freemem shows freelist + cachelist, where cachelist is the UFS cache which is considered FREE because it gives back memory to applications. At this moment, ZFS does not have anything like cachelist to report how much memory to give back so we are back to reactive mode again. Yes there are other memory related barriers such as the large pages you talked about, but they don't cause drastic performance degradation as paging/swapping does. So we might consider them in performance tuning area instead of capacity planning area. And yes memory are cheaper and cheaper these days but with server consolidation and virtualization, the need for capacity planning is not really decreasing. With ::memstat, yes it may be possible to have a rough idea of free memory but as you said it's quite intrusive and it requires admin privilege. If, with dTrace or whatever tools out there we can have a clearly or vaguely defined algorithm (such as the one developed by benr) to help find out free memory again it'll help customers a lot. Just as a real life example, consider two machines, one with UFS/Vxfs, the other with UFS/ZFS. The first one can, right or wrong, tell you the rough percentage memory in used, while the latter one can not. Also here's the ::memstat output from ultra5 (don't laugh, I am still using it) > ::memstat Page Summary Pages MB %Tot ------------ ---------------- ---------------- ---- Kernel 40416 315 32% ZFS File Data 53697 419 42% Anon 23303 182 18% Exec and libs 1108 8 1% Page cache 4333 33 3% Free (cachelist) 3153 24 2% Free (freelist) 2175 16 2% Total 128185 1001 Physical 127490 996 Without ZFS, the two rows marked as Free will give me an idea of free memory, but it's getting too vague with ZFS. -- This message posted from opensolaris.org _______________________________________________ perf-discuss mailing list perf-discuss@opensolaris.org
