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

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Date:   Wed, 27 Oct 2021 14:14:57 +0800
From:   Xiongfeng Wang <wangxiongfeng2@...wei.com>
To:     <sj@...nel.org>
CC:     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

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.
> 
> 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 !
> 
> Thanks,
> Xiongfeng
>