Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

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Matt Mackall wrote:
On Fri, Apr 13, 2007 at 11:42:29AM +1000, Nick Piggin wrote:

If kprobes is simply crappy and doesn't work properly for this, then I
could accept that. I'm not someone trying to get this info. So why can't
it be used? (not just for kpagemap, but for clear_refs and all that gunk
too).


kprobes is good for looking at events, but bad for looking at state.
Especially metric shitloads of state.

Why? Why is a kprobes trap significantly more expensive than a read
syscall?

Maybe. How about LRU? Reclaim performance is bad, and you want to work out
which pages keep going off the end of it, or which pages keep getting
written out via it, or who's pages are on the active list, forcing mine
out.


Those are actually probably a good match for systemtap as they're all events.

Traverse the LRU? Which files do they belong to? What process maps them?

--
SUSE Labs, Novell Inc.
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