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

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Message-ID: <20070413065545.GQ2986@holomorphy.com>
Date:	Thu, 12 Apr 2007 23:55:45 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

Andrew Morton wrote:
>> 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.  Then you just end up with the same thing, don't you?

On Fri, Apr 13, 2007 at 01:40:08PM +1000, Nick Piggin wrote:
> And my problem isn't with the hardcoded pagetable walker. Yeah, we'd
> probably still keep the pagetable callback walker thingy with Matt's
> associated cleanups (and my subsequent ones to clean it up more and
> move it to mm/): there are other in-kernel users for that anyway.
> The point is the proc API, and exposing random little parts of deep
> kernel internals that some people happen to find useful at the time.
> (which is why we have an incredible proliferation of these things).
> 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).

The EM guys are unwilling or unable for support-oriented reasons to
deal with anything but unmodified kernels as shipped by distros.


-- wli
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