linux-kernel - Re: [PATCH] tracing/kmemtrace: normalize the raw tracer event to the unified tracing API

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Message-ID: <20081230084127.GE10635@localhost>
Date:	Tue, 30 Dec 2008 10:41:27 +0200
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] tracing/kmemtrace: normalize the raw tracer event to
	the unified tracing API

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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