Page size and disk access
Posted Jun 30, 2006 9:52 UTC (Fri) by forthy
Parent article: KHB: Transparent support for large pages
TLB hit rate is one performance issue with page sizes, but there's
another: disk access.
If you are lucky, you can do a 100 accesses to a hard disk per second.
On the other hand, you can read 60MB or more per second, if you read
sequentially. So the 4k page size is way smaller than what's a reasonable
access patter to a hard disk today - 512k would be closer to the sweet
spot at the moment (where seek time and transfer time are similar). But
since transfer time increases over time, while seek time doesn't change
much, sweet spots move as well.
So support for lage pages also should look at how to interface with
disks. If I have a page miss on a 700k executable, which is currently
populating its text segment, it makes more sense to just allocate a 512k
page right now, fetch this chunk in one go, and later, when memory
is tight, and 2/3 of this page is never used, split it up, and release
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