Per-mount syncer threads and fanout for pagedaemon cleaning

[Giovanni Trematerra]

On Mon, Dec 26, 2011 at 9:24 PM, Venkatesh Srinivas
<vsrinivas at dragonflybsd.org> 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.

--
Gianni