Re: linux-2.4.10-pre5

Alan Cox
2001-09-09T23:51:56Z

How do you plan to handle the situation where we have multiple instances
of the same 4K disk block each of which contains 1K of data in the
start of the page copy and 3K of zeroes.

This isnt idle speculation - thing about BSD UFS fragments.

> anyway, I very much doubt it has any good properties to make software more
> complex by having that kind of readahead in sw.

Even the complex stuff like the i2o raid controllers seems to benefit
primarily from file level not physical readahead, that gives it enough to
do intelligent scheduling and to keep the drive firmware busy making good
decisions (hopefully)

Even with software raid the physical readahead decisions belong in the raid
code as they are tied to strip alignment and sizes not high level policy

Alan