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

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Andrew Morton wrote:
On Fri, 13 Apr 2007 12:18:56 +1000 Nick Piggin <[email protected]> wrote:


I guess one could generate an answer to the static question with systemtap,
by accumulating running counts across the application lifetime and then
snapshotting them.  Sounds hard though.

Can't you just traverse arbitrary kernel data structures at a given point
in time, exactly like the /proc/ call is doing?


Do a full pagetable walk, with all the associated locking from within
a systemtap script?  I'd be surprised.  Maybe if it's mostly hand-coded
in C, perhaps.

It looks like you can traverse arbitrary data structures, yes.

It definitely seems like you can use some kernel functions, but the
ones I saw may just be systemtap facilities. But what is so surprising
about being able to call a kernel function when running in kernel
context? Perhaps there is some fundamental limitation of kprobes that
I don't understand.

 Then you just end up with the same thing, don't you?

Well _you_ do, because that happens to be exactly what you want. Bill
ends up with something that displays page_mapcount instead. And I
end up with something that traverses LRU lists rather than pfns. And
none of it goes in /proc/ or linux-2.6/.

So it isn't really the same thing at all.

--
SUSE Labs, Novell Inc.
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