On Tue, Dec 27, 2011 at 8:05 AM, Attilio Rao <[email protected]> wrote: > 2011/12/27 Giovanni Trematerra <[email protected]>: >> On Mon, Dec 26, 2011 at 9:24 PM, Venkatesh Srinivas >> <[email protected]> wrote: >>> Hi! >>> >>> I've been playing with two things in DragonFly that might be of interest >>> here. >>> >>> Thing #1 := >>> >>> First, per-mountpoint syncer threads. Currently there is a single thread, >>> 'syncer', which periodically calls fsync() on dirty vnodes from every mount, >>> along with calling vfs_sync() on each filesystem itself (via syncer vnodes). >>> >>> My patch modifies this to create syncer threads for mounts that request it. >>> For these mounts, vnodes are synced from their mount-specific thread rather >>> than the global syncer. >>> >>> The idea is that periodic fsync/sync operations from one filesystem should >>> not >>> stall or delay synchronization for other ones. >>> The patch was fairly simple: >>> http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/50e4012a4b55e1efc595db0db397b4365f08b640 >>> >> >> There's something WIP by attilio@ on that area. >> you might want to take a look at >> http://people.freebsd.org/~attilio/syncer_alpha_15.diff >> >> I don't know what hammerfs needs but UFS/FFS and buffer cache make a good >> job performance-wise and so the authors are skeptical about the boost that >> such >> a change can give. We believe that brain cycles need to be spent on >> other pieces of the system such as ARC and ZFS. > > More specifically, it is likely that focusing on UFS and buffer cache > for performance is not really useful, we should drive our efforts over > ARC and ZFS. > Also, the real bottlenecks in our I/O paths are in GEOM > single-threaded design, lack of unmapped I/O functionality, possibly > lack of proritized I/O, etc.
Indeed, Isilon (and probably other vendors as well) entirely skip VFS_SYNC when the WAIT argument is MNT_LAZY. Since we're a distributed journalled filesystem, syncing via a system thread is not a relevant operation; i.e. all writes that have exited a VOP_WRITE or similar operation are already in reasonably stable storage in a journal on the relevant nodes. However, we do then have our own threads running on each node to flush the journal regularly (in addition to when it fills up), and I don't know enough about this to know if it could be fit into the syncer thread idea or if it's too tied in somehow to our architecture. Cheers, matthew _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
