Re: [ANNOUNCE] iSCSI enterprise target software

[Jeff Garzik <jgarzik@pobox.com>]

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.

As does mmap/sendfile...

	Jeff