Re: bio_chain: proposed solution for bio_alloc failure and large IO simplification

[William Lee Irwin III <wli@holomorphy.com>]

On Fri, Jun 14, 2002 at 04:00:52PM -0700, Andrew Morton wrote:
> Everything is pretty much in place to do this now.  The main piece
> which is missing is the gang page allocator (Hi, Bill).
> It'll be damn fast, and nicely scalable.  It's all about reducing the
> L1 cache footprint.  Making best use of data when it is in cache.
> Making best use of locks once they have been acquired.  If it is
> done right, it'll be almost as fast as 64k PAGE_CACHE_SIZE, with
> none of its disadvantages.
> In this context, bio_chain() is regression, because we're back
> into doing stuff once-per-page, and longer per-page call graphs.
> I'd rather not have to do it if it can be avoided.

gang_cpu is not quite ready to post, but work is happening on it
and it's happening today -- I have a suitable target in hand and 
am preparing it for testing. The bits written thus far consist of
a transparent per-cpu pool layer refilled using the gang transfer
mechanism, and I'm in the process of refining that to non-prototypical
code and extending it with appropriate deadlock avoidance so explicit
gang allocation requests can be satisfied.


Cheers,
Bill