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Date: Tue, 30 Dec 2008 10:41:27 +0200
From: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
To: Ingo Molnar <mingo@elte.hu>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] tracing/kmemtrace: normalize the raw tracer event to
	the unified tracing API
Message-ID: <20081230084127.GE10635@localhost>
References: <4959443f.09a1660a.44f3.2686@mx.google.com> <20081229220937.GC5829@nowhere> <1230623364.6091.9.camel@penberg-laptop> <20081230081600.GD2455@elte.hu>
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On Tue, Dec 30, 2008 at 09:16:00AM +0100, Ingo Molnar wrote:
> 3)
> 
> the most lowlevel (and hence most allocation-footprint sensitive) object 
> to track would be the memory object itself. I think the best approach 
> would be to do a static, limited size hash that could track up to N memory 
> objects.
> 
> The advantage of such an approach is that it does not impact allocation 
> patterns at all (besides the one-time allocation cost of the hash itself 
> during tracer startup).

kmemtrace-user handles this by analysing offline :). I presume you could get
around this by discarding every hash collision in a well-sized
hashtable. The hashing algo in kmemtrace-user performs okay, considering
it fills the hashtable almost entirely, but I presume you're doing that
in-kernel and using other available code.

> And this too would be driven from ftrace mainly - the SLAB code would only 
> offer the alloc+free callbacks with the object IDs. [ and this means that 
> we could detect memory leaks by looking at the hash table and print out 
> the age of entries :-) ]

Some time ago I dropped timestamps because they were not providing a
good way to reorder packets in userspace. We're currently relying on a
sequence number to do that. You could take that as 'age', but it's not
temporally-meaningful.


	Eduard

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