linux-kernel - Re: DAMON: problems when running DAMON on ARM64 with 'transparent

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Message-Id: <20211027080636.14886-1-sj@kernel.org>
Date:   Wed, 27 Oct 2021 08:06:36 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     sj@...nel.org, Kefeng Wang <wangkefeng.wang@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: DAMON: problems when running DAMON on ARM64 with 'transparent_hugepage' enabled

Hello Xiongfeng,

On Wed, 27 Oct 2021 14:14:57 +0800 Xiongfeng Wang <wangxiongfeng2@...wei.com> wrote:

> Sorry, I forgot to Cc the maillist. Cc it in this mail.
> 
> On 2021/10/27 10:19, Xiongfeng Wang wrote:
> > Hi SeongJae,
> > 
> > Sorry to disturb you. It's just that I came across some problems when running
> > DAMON, but still didn't find the solution after several days.

You're not disturbing but helping me!  Please don't say so! :)

> > 
> > A short description is that the result of DAMON is not as expected when running
> > on ARM64 with 'transparent_hugepage' enabled. But the result is correct when
> > 'transparent_hugepage' is disabled.
> > 
> > The following are the steps I came across the problems.
> > 1. Firstly, I use 'damo record' to sample the 'stairs' demo.
> >   damo record "./masim ./configs/stairs.cfg"
> > 2. Then I use 'damo report' to show the results.
> >   damo report heats --address_range xxx  xxx  --time_range xxx xxx    --heatmap
> > stdout    --stdout_heatmap_color emotion
> > The result doesn't show like a stair. I wrote a userspace demo to access a
> > certain address range in loop and use DAMON to sample the demo. I added
> > trace_print in 'damon_va_check_access()' and found out the pages in the address
> > range are not always detected as accessed, which is not expected. When I disable
> > transparent_hugepage by chance, the pages are marked as accessed. Then I test
> > the 'stairs' demo again, the result is correct. It seems that, only when
> > transparent_hugepage' is disabled, the access check works. I don't know where
> > the bug is, the software or the hardware ? Appreciate it if you have time to
> > reply. Thanks !

Thank you for this report!  I have a theory, but would like to test first.
Will check and get back to you soon.


Thanks,
SJ

> > 
> > Thanks,
> > Xiongfeng