Message-ID: <1437082414.12633.52.camel@tzanussi-mobl.amr.corp.intel.com>
Subject: Re: [PATCH v9 07/22] tracing: Add lock-free tracing_map
From: Tom Zanussi <tom.zanussi@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rostedt@goodmis.org, daniel.wagner@bmw-carit.de,
        masami.hiramatsu.pt@hitachi.com, namhyung@kernel.org,
        josh@joshtriplett.org, andi@firstfloor.org,
        linux-kernel@vger.kernel.org
Date: Thu, 16 Jul 2015 16:33:34 -0500
In-Reply-To: <20150716180348.GI12596@twins.programming.kicks-ass.net>
References: <cover.1437066836.git.tom.zanussi@linux.intel.com>
	 <777bd36975a1dd904fd6b72c4048474dd2327a65.1437066836.git.tom.zanussi@linux.intel.com>
	 <20150716180348.GI12596@twins.programming.kicks-ass.net>
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On Thu, 2015-07-16 at 20:03 +0200, Peter Zijlstra wrote:
> On Thu, Jul 16, 2015 at 12:22:40PM -0500, Tom Zanussi wrote:
> > +	map->map = kcalloc(map->map_size, sizeof(struct tracing_map_entry),
> > +			   GFP_KERNEL);
> 
> In a later email you state the max map size to be 128k, with a 16 byte
> struct, that is 2m of memory for this allocation.
> 
> Isn't that a tad big for a kmalloc() ?

Yeah, that is a bit big for kmalloc (actually it's double that), though
I never ran into problems in my testing (of course that would depend on
the state of the system, and I mainly tested on a newly booted system).

It would probably make sense to make it page-based, which means a bit
more complicated mapping for the array (can't use vmalloc here) but that
shouldn't be too big a deal.

Tom

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