linux-kernel - Re: [PATCH 10/19] x86, mpx: Trace the attempts to find bounds tables

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Message-ID: <alpine.DEB.2.11.1505191017440.4225@nanos>
Date:	Tue, 19 May 2015 10:17:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 10/19] x86, mpx: Trace the attempts to find bounds
 tables

On Mon, 18 May 2015, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> There are two different events being traced here.  They are
> doing similar things so share a trace "EVENT_CLASS" and are
> presented together.
> 
> 1. Trace when MPX is zapping pages "mpx_unmap_zap":
> 
> 	When MPX can not free an entire bounds table, it will
> 	instead try to zap unused parts of a bounds table to free
> 	the backing memory.  This decreases RSS (resident set
> 	size) without decreasing the virtual space allocated
> 	for bounds tables.
> 
> 2. Trace attempts to find bounds tables "mpx_unmap_search":
> 
> 	This event traces any time we go looking to unmap a
> 	bounds table for a given virtual address range.  This is
> 	useful to ensure that the kernel actually "tried" to free
> 	a bounds table versus times it succeeded in finding one.
> 
> 	It might try and fail if it realized that a table was
> 	shared with an adjacent VMA which is not being unmapped.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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