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Subject: Re: [RFC PATCH] watchdog: Adding softwatchdog
To:     Guenter Roeck <linux@roeck-us.net>,
        Peter Enderborg <peter.enderborg@sony.com>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>
References: <20210424102555.28203-1-peter.enderborg@sony.com>
 <20210424102555.28203-2-peter.enderborg@sony.com>
 <d5db5606-f074-6d0e-2316-8ff41af25cfd@roeck-us.net>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <844e3ecb-62c3-856a-7273-e22eee35e80f@i-love.sakura.ne.jp>
Date:   Sun, 25 Apr 2021 00:23:32 +0900
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On 2021/04/24 23:41, Guenter Roeck wrote:
> On 4/24/21 3:25 AM, Peter Enderborg wrote:
>> This is not a rebooting watchdog. It's function is to take other
>> actions than a hard reboot. On many complex system there is some
>> kind of manager that monitor and take action on slow systems.
>> Android has it's lowmemorykiller (lmkd), desktops has earlyoom.
>> This watchdog can be used to help monitor to preform some basic
>> action to keep the monitor running.
>>
>> It can also be used standalone. This add a policy that is
>> killing the process with highest oom_score_adj and using
>> oom functions to it quickly. I think it is a good usecase
>> for the patch. Memory siuations can be problematic for
>> software that monitor system, but other prolicys can
>> should also be possible. Like picking tasks from a memcg, or
>> specific UID's or what ever is low priority.
>> ---
> 
> NACK. Besides this not following the new watchdog API, the task
> of a watchdog is to reset the system on failure. Its task is most
> definitely not to re-implement the oom killer in any way, shape,
> or form.
> 

I don't think this proposal is a watchdog. I think this proposal is
a timer based process killer, based on an assumption that any slowdown
which prevents the monitor process from pinging for more than 0.5 seconds
(if HZ == 1000) is caused by memory pressure.