On Sat, Jul 04, 2009 at 07:18:45PM +0100, Phil Harman wrote: > Gary Mills wrote: > >On Sat, Jul 04, 2009 at 08:48:33AM +0100, Phil Harman wrote: > > > >>ZFS doesn't mix well with mmap(2). This is because ZFS uses the ARC > >>instead of the Solaris page cache. But mmap() uses the latter. So if > >>anyone maps a file, ZFS has to keep the two caches in sync. > > > >That's the first I've heard of this issue. Our e-mail server runs > >Cyrus IMAP with mailboxes on ZFS filesystems. Cyrus uses mmap(2) > >extensively. I understand that Solaris has an excellent > >implementation of mmap(2). ZFS has many advantages, snapshots for > >example, for mailbox storage. Is there anything that we can be do to > >optimize the two caches in this environment? Will mmap(2) one day > >play nicely with ZFS? > [..] > Software engineering is always about prioritising resource. Nothing > prioritises performance tuning attention quite like compelling > competitive data. When Bart Smaalders and I wrote libMicro we generated > a lot of very compelling data. I also coined the phrase "If Linux is > faster, it's a Solaris bug". You will find quite a few (mostly fixed) > bugs with the synopsis "linux is faster than solaris at ...". > > So, if mmap(2) playing nicely with ZFS is important to you, probably the > best thing you can do to help that along is to provide data that will > help build the business case for spending engineering resource on the issue.
First of all, how significant is the double caching in terms of performance? If the effect is small, I won't worry about it anymore. What sort of data do you need? Would a list of software products that utilize mmap(2) extensively and could benefit from ZFS be suitable? As for a business case, we just had an extended and catastrophic performance degradation that was the result of two ZFS bugs. If we have another one like that, our director is likely to instruct us to throw away all our Solaris toys and convert to Microsoft products. -- -Gary Mills- -Unix Support- -U of M Academic Computing and Networking- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
