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

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Date:	Fri, 13 Apr 2007 17:03:43 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	William Lee Irwin III <wli@...omorphy.com>
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

William Lee Irwin III wrote:
> 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.

And I think major distros ship with kprobes enabled, so that is yet
another reason why systemtap should be considered before adding these
proc interfaces.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.
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