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Date: Fri, 13 Apr 2007 12:21:25 +1000 From: Nick Piggin <nickpiggin@...oo.com.au> To: Matt Mackall <mpm@...enic.com> CC: Andrew Morton <akpm@...ux-foundation.org>, William Lee Irwin III <wli@...omorphy.com>, linux-kernel@...r.kernel.org Subject: Re: [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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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