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

Nick Piggin
2007-04-13T02:21:34Z

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.