Re: Exposing FUA as alternative to DIOCCACHESYNC for WAPBL

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Sat, Apr 01, 2017 at 06:46:24PM +0200, Michael van Elst wrote:
> On Sat, Apr 01, 2017 at 11:12:42AM -0400, Thor Lancelot Simon wrote:
> 
> > That said, very high-latency transports like iSCSI require a lot more
> > data than we can put into flight at once.  We just don't have enough
> > parallelism in our I/O subsystem (and most applications can't supply
> > enough).
> 
> We have tons of parallelism for writing and a small amount for reading.

Unless you've done even more than I noticed, allocation in the filesystems
is going to be a bottleneck -- concurrent access not having been foremost
in anyone's mind when FFS was designed.

XFS is full of tricks for this.  Unfortunately, despite a few early papers,
the source code pretty much is the documentation -- and parts of the code
that were effectively hamstrung by the lesser capabilities of the early
Linux kernel compared to end-of-the-road Irix have in some cases been
removed.

-- 
  Thor Lancelot Simon	                                     tls%panix.com@localhost

  "We cannot usually in social life pursue a single value or a single moral
   aim, untroubled by the need to compromise with others."      - H.L.A. Hart