linux-kernel - Re: [RFC][PATCH 0/1] kmemleak: Fix false positive with alias

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Date:	Tue, 22 Jun 2010 18:36:33 +0300
From:	Phil Carmody <ext-phil.2.carmody@...ia.com>
To:	"Doyu Hiroshi (Nokia-D/Helsinki)" <hiroshi.doyu@...ia.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/1] kmemleak: Fix false positive with alias

On 18/06/10 08:04 +0200, Doyu Hiroshi (Nokia-D/Helsinki) wrote:
> Hi,
> 
> This is another version of "kmemleak: Fix false positive", which
> introduces another alias tree to keep track of all alias address of
> each objects, based on the discussion(*1)
> 
> You can also find the previous one(*2), which uses special scan area
> for alias addresses with a conversion function.
> 
> Compared with both methods, it seems that the current one takes a bit
> longer to scan as below, tested with 512 elementes of (*3).
> 
> "kmemleak: Fix false positive with alias":
> # time echo scan > /mnt/kmemleak
> real    0m 8.40s
> user    0m 0.00s
> sys     0m 8.40s
> 
> "kmemleak: Fix false positive with special scan":
> # time echo scan > /mnt/kmemleak 
> real    0m 3.96s
> user    0m 0.00s
> sys     0m 3.96s
> 
> For our case(*4) to reduce false positives for the 2nd level IOMMU
> pagetable allocation, the previous special scan  seems to be enough
> lightweight, although there might be possiblity to improve alias
> one and also I might misunderstand the original proposal of aliasing.
> 
> Any comment would be appreciated.

After comparing the two, my Ack would still strongly be behind the 
first one, the special scan. The additional work over a normal scan 
is limited strictly to those regions that need it, which is a much 
more clinical approach to the problem. Your timing data bears that 
out.

Phil

> *1: http://lkml.org/lkml/2010/6/2/282
> *2: kmemleak: Fix false positive with special scan
>     http://lkml.org/lkml/2010/6/1/137
> *3: kmemleak: Add special scan test case
>     http://lkml.org/lkml/2010/6/1/134
> *4: http://lkml.org/lkml/2010/6/1/136
> 
> Hiroshi DOYU (1):
>   kmemleak: Fix false positive with alias
> 
>  include/linux/kmemleak.h |    4 +
>  mm/kmemleak.c            |  198 ++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 168 insertions(+), 34 deletions(-)
> 
> 
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