Re: [ANNOUNCE] iSCSI enterprise target software

[Andi Kleen <ak@muc.de>]

Arjan van de Ven <arjan@infradead.org> writes:
>
> You want to *use* the kernel pagecache as much as you can. You do so by
> using mmap and such, and msync to force content to disk. That uses the

Last time I checked you couldn't mmap block devices. Has this changed
now?  Could be a problem for an iSCSI target.

I remember there used to be a hack in 2.2 to map them to a pseudo fs
to allow mmaping, but that's not very nice and would require
another step by the administrator.

Also using mmap would imply the server only works on 64bit systems,
and may even there have uncomfortable limits. One issue is that
the kernel currently doesn't garbage collect page tables, so 
e.g. when you map a 10TB volume this way and the user accesses
it randomly you will eventually have quite a lot of page tables
filling up your RAM. And those will not go away.

My overall feeling is that mmap is not a good idea for this.

-Andi