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

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Message-ID: <20070413140827.GA8864@thunk.org>
Date:	Fri, 13 Apr 2007 10:08:27 -0400
From:	Theodore Tso <tytso@....edu>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

On Fri, Apr 13, 2007 at 01:40:08PM +1000, Nick Piggin wrote:
> With systemtap scripts, you could walk pagetables and print *the exact
> page information you want*, or you could walk pfns, or LRU, or page_tree,
> or walk the page tree then the rmap structures. And you can selectively
> cull out items you don't care about if you only care about a subset of
> items, based on arbitrary criteria. And you can most likely do all that
> more efficiently than with a conglomeration of various /proc files
> (assuming they even provide what you want in the first place).

Yes, but maintaining the systemtap scripts will be a nightmare, since
they would be outside the kernel, and as we change our internal data
structure, the scripts would become useless.

This is a fundamental problem with systemtap that we haven't been able
to solve yet, because solving it would freeze various internal data
structures or kernel functions.  I agree that's not acceptable; which
is why I don't think systemtap would be a good match for the problem
we're trying to solve here.

						- Ted
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