Certainly something we'll have to tackle. How about a zpool memstat (or zpool -m iostat) variation that would report at least freemem and the amount evictable cached data ?
Would that work for you ? -r Philip Beevers writes: > Roch Bourbonnais - Performance Engineering wrote: > > >Reported freemem will be lower when running with ZFS than > >say UFS. The UFS page cache is considered as freemem. ZFS > >will return it's 'cache' only when memory is needed. So you > >will operate with lower freemem but won't actually suffer > >from this. > > > >It's been wrongly feared that this mode of operation puts us > >back to the days of Solaris 2.6 and 7 where we saw a roaller > >coaster effect on freemem leading to sub-par application > >performance. We actually DO NOT have this problem with ZFS. > >The old problem came because the memory reaper could > >distinguish between a useful application page and an UFS > >cached page. That was bad. ZFS frees up it's cache in a way > >that does not cause a problem. > > > > > Thanks for the very informative write-up. This clears a few issues for > me, at least. > > However, I'm still a bit worried that we'll be running with a lower > freemem value. The issue here is one of provisioning and capacity > planning - or put another way, how do I know when I've got enough memory > if freemem is always low? Having a freemem value we could believe in - > as well as the corresponding performance improvements - was a huge win > for us when Solaris 8 came along, and it makes it very easy to see when > we're out of memory. For example, in our production environments at work > we have automated monitoring which alerts us when freemem drops below a > particular %age of the total physical memory on the machine; it sounds > like ZFS is going to break this. > > Is there any way (preferably a simple one) to get the same > easy-to-understand figure when ZFS is in use, or am I missing something? > > > Thanks, > > > Phil. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
