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SubjectRe: How can we make page replacement smarter (was: swap-prefetch)
Al Boldi wrote:
> Chris Snook wrote:

>> At best, reads can be read-ahead and cached, which is why
>> sequential swap-in sucks less. On-demand reads are as expensive as I/O
>> can get.
>
> Which means that it should be at least as fast as swap-out, even faster
> because write to disk is usually slower than read on modern disks. But
> linux currently shows a distinct 2x slowdown for sequential swap-in wrt
> swap-out.

That's because writes are faster than reads in moderate
quantities.

The disk caches writes, allowing the OS to write a whole
bunch of data into the disk cache and the disk can optimize
the IO a bit internally.

The same optimization is not possible for reads.

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calls the other unpatriotic.
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