Re: [9fans] gar nix!

[ron minnich <rminnich@gmail.com>]

for the 2M pages -- I'm willing to see some measurement but let's get
the #s -- I've done some simple measurements and it's not the hit one
would expect. These new machines have about 10 GB/s bandwidth (well,
the ones we are targeting do) and that translates to sub-millisecond
times to zero a 2M page. Further, the text page is in the image cache.
So after first exec of a program, the only text issue is locating the
page. It's not simply a case of having to write 6M each time you exec.

I note that starting a proc, allocating and zeroing 2 GiB, takes
*less* time with 2M pages than 4K pages -- this was measured in May
when we still were supporting 4K pages -- the page faults are far more
expensive than the time to write the memory. Again, YMMV, esp. on an
Atom, but the cost of taking (say) 6 page faults for a 24k text
segment that's already in memory may not be what you want.

There are plenty of games to be played to reduce the cost of zero
filled pages but at least from what I measured the 2M pages are not a
real hit.

ron