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Subject: Re: [PATCH v16 18/22] mm/lru: replace pgdat lru_lock with lruvec lock
To:     Alexander Duyck <alexander.duyck@gmail.com>
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From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <27eb389d-b5f9-fe03-2e57-15c351629efc@linux.alibaba.com>
Date:   Mon, 20 Jul 2020 13:47:09 +0800
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在 2020/7/19 下午11:14, Alexander Duyck 写道:
>> Compare to move to tail, how about to move it to head of struct, which is
>> close to lru list? Did you have some data of the place change?
> I don't have specific data, just anecdotal evidence from the past that
> usually you want to keep locks away from read-mostly items since they
> cause obvious cache thrash. My concern was more with the other fields
> in the structure such as pgdat since it should be a static value and
> having it evicted would likely be more expensive than just leaving the
> cacheline as it is.
> 

Thanks for comments, Alex.

So, sounds like moving the lru_lock to head of struct lruvec could be better.

>> -       __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
>> +       if (delta_munlocked)
>> +               __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
>>         if (lruvec)
>>                 unlock_page_lruvec_irq(lruvec);
> Why not just wrap the entire thing in a check for "lruvec"? Yes you
> could theoretically be modding with a value of 0, but it avoids a
> secondary unnecessary check and branching.

Right, and the delta_munlocked value could be checked inside the accounting
func

Thanks!