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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH v3 4/9] cgroup/cpuset: Enable event notification when
 partition become invalid
To:     Tejun Heo <tj@kernel.org>
Cc:     Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Phil Auld <pauld@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
References: <20210720141834.10624-1-longman@redhat.com>
 <20210720141834.10624-5-longman@redhat.com>
 <YP9BxKXfhaoTE+LO@slm.duckdns.org>
Message-ID: <8bed1ac2-f5f4-6d17-d539-4cd274b0f39e@redhat.com>
Date:   Tue, 27 Jul 2021 16:26:31 -0400
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On 7/26/21 7:14 PM, Tejun Heo wrote:
> On Tue, Jul 20, 2021 at 10:18:29AM -0400, Waiman Long wrote:
>> +static inline void notify_partition_change(struct cpuset *cs,
>> +					   int old_prs, int new_prs)
>> +{
>> +	if ((old_prs == new_prs) ||
>> +	   ((old_prs != PRS_ERROR) && (new_prs != PRS_ERROR)))
>> +		return;
>> +	cgroup_file_notify(&cs->partition_file);
> I'd generate an event on any state changes. The user have to read the file
> to find out what happened anyway.
>
> Thanks.

 From my own testing with "inotify_add_watch(fd, file, IN_MODIFY)", 
poll() will return with a event whenever a user write to 
cpuset.cpus.partition control file. I haven't really look into the sysfs 
code yet, but I believe event generation will be automatic in this case. 
So I don't think I need to explicitly add a cgroup_file_notify() when 
users modify the control file directly. Other indirect modification may 
cause the partition value to change to/from PRS_ERROR and I should have 
captured all those changes in this patchset. I will update the patch to 
note this point to make it more clear.

Cheers,
Longman