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SubjectRe: 2.5.59-mm5
Andrew Morton writes:


> In this very common scenario, the only way we'll ever get "lumps" of reads is
> if some other processes come in and happen to want to read nearby sectors.

Or if you have read-ahead for meta-data, which is quite useful. Isn't
read ahead targeting the same problem as this anticipatory scheduling?

> In the best case, the size of the lump is proportional to the number of
> processes which are concurrently trying to read something. This just doesn't
> happen enough to be significant or interesting.
> But writes are completely different. There is no dependency between them and
> at any point in time we know where on-disk a lot of writes will be placed.
> We don't know that for reads, which is why we need to twiddle thumbs until the
> application or filesystem makes up its mind.

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