Re: [PATCH 3/3] mm/memcg: move generation assignment and comparison together

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On Wed, Mar 30, 2022 at 11:57:07AM -0400, Johannes Weiner wrote:
>On Fri, Feb 25, 2022 at 12:34:37AM +0000, Wei Yang wrote:
>> For each round-trip, we assign generation on first invocation and
>> compare it on subsequent invocations.
>> 
>> Let's move them together to make it more self-explaining. Also this
>> reduce a check on prev.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>
>This makes sense. The function is structured into 1) load state, 2)
>advance, 3) save state. The load state is a better fit for
>initializing reclaim->generation.
>
>> @@ -996,7 +996,14 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>>  		mz = root->nodeinfo[reclaim->pgdat->node_id];
>>  		iter = &mz->iter;
>>  
>> -		if (prev && reclaim->generation != iter->generation)
>> +		/*
>> +		 * On first invocation, assign iter->generation to
>> +		 * reclaim->generation.
>> +		 * On subsequent invocations, make sure no one else jump in.
>> +		 */
>> +		if (!prev)
>> +			reclaim->generation = iter->generation;
>> +		else if (reclaim->generation != iter->generation)
>>  			goto out_unlock;
>
>The comment duplicates the code, it doesn't explain why we're doing
>this. How about:
>
>		/*
>		 * On start, join the current reclaim iteration cycle.
>		 * Exit when a concurrent walker completes it.
>		 */

This one looks better and explain the reclaim model.
Thanks

>
>With that, please feel free to add:
>
>Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

-- 
Wei Yang
Help you, Help me



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