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