Re: wapbl_flush() speedup

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

On Tue, Dec 04, 2012 at 07:10:47PM +0000, Michael van Elst wrote:
> hannken%eis.cs.tu-bs.de@localhost ("J. Hannken-Illjes") writes:
> 
> >The attached diff tries to coalesce writes to the journal in MAXPHYS
> >sized and aligned blocks.
> [...]
> >Comments or objections anyone?
> 
> >+ * Write data to the log.
> >+ * Try to coalesce writes and emit MAXPHYS aligned blocks.
> 
> Looks fine, but I would prefer the code to use an arbitrarily sized
> buffer in case we get individual per device transfer limits. Currently
> that size would still be MAXPHYS, but then the code could query the driver
> for a proper size.

In fact, this patch and the discussion that led up to it have me
planning to replace the simple per-device "maximum transfer length"
currently implemented on the tls-maxphys branch with at least three
different properties:

        * An upper-bound (the maximum transfer length)
        * A lower-bound (the minimum atomic transfer length)
        * An optimal transfer alignment

Exposing all these to the right code elsewhere in the kernel won't be
so easy, but I'm working on it (slowly).

Thor