>> Given that, cp could do the readahead.  But do you really want it
>> to?  I don't see why it should have to.
> me too

>> What you really want is a way to tell the kernel that buffers filled
>> solely to satisfy this I/O should be aged into oblivion once the I/O
>> completes, so that they are _first_ to be re-used.
> [...] BUT direct I/O mean NO buffers at all = directly read data to
> userspace (NO MEMCPY)

Yes.  But it also means no readahead, because there's nowhere to _put_
the readahead.  (Unless the application provides such a place, which we
agreed it shouldn't need to do.)

As for the memcpy, I'd rather memcpy from buffers than wait for a disk
transfer - even a transfer that hits the disk's track cache.

/~\ The ASCII				der Mouse
\ / Ribbon Campaign
 X  Against HTML	       mouse@rodents.montreal.qc.ca
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B