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SubjectRe: [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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