Subject: Re: RAW access to files
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-kern
Date: 12/12/2001 22:27:55
>> 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.

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