Re: [PATCH v16 18/22] mm/lru: replace pgdat lru_lock with lruvec lock

[Alex Shi <alex.shi@linux.alibaba.com>]

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!