Re: [ANNOUNCE] iSCSI enterprise target software

[Ming Zhang <mingz@ele.uri.edu>]

On Tue, 2005-03-01 at 14:01, Jeff Garzik wrote:
> Ming Zhang wrote:
> > On Tue, 2005-03-01 at 13:37, Arjan van de Ven wrote:
> > 
> >>On Tue, 2005-03-01 at 10:24 -0800, Bryan Henderson wrote:
> >>
> >>>One thing that's implicit in your reasons for wanting to be in the kernel 
> >>>is that you've chosen to exploit the kernel's page cache.  As a user of 
> >>>the page cache, you have more control from inside the kernel than from 
> >>>user space.  The page cache was designed to be fundamentally invisible to 
> >>>user space.
> >>>
> >>>A pure user space implementation of an ISCSI target would use process 
> >>>virtual memory for a cache and manage it itself.  It would access the 
> >>>storage with direct I/O. 
> >>
> >>why would it use direct I/O ? Direct I/O would be really stupid for such
> >>a thing to use since that means there's no caching going on *at all*.
> >>
> > 
> > what Bryan suggest is a privately owned and managed user space cache. so
> > for that disk write should be real write-through.
> > 
> > it is hard to beat linux kernel cache performance though.
> 
> A privately managed user space cache uses Linux kernel cache.
what i mean is private cache algorithms. for example, windows request
are not page size aligned so some bitmap based cache algorithms might be
useful. 

> 
> As does mmap/sendfile...
> 
> 	Jeff
>