Re: How can we make page replacement smarter (was: swap-prefetch)

Al Boldi wrote:

Chris Snook wrote:

quoted

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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