Re: [PATCH v15 3/7] mm: Add function __putback_isolated_page

David Hildenbrand
2019-12-17T17:25:00Z

>>> Also there are some scenarios where __page_to_pfn is not that simple a
>>> call with us having to get the node ID so we can find the pgdat structure
>>> to perform the calculation. I'm not sure the compiler would be ble to
>>> figure out that the result is the same for both calls, so it is better to
>>> make it explicit.
>>
>> Only in case of CONFIG_SPARSEMEM we have to go via the section - but I
>> doubt this is really worth optimizing here.
>>
>> But yeah, I'm fine with this change, only "IMHO
>> get_pageblock_migratetype() would be nicer" :)
>
> Aren't most distros running with CONFIG_SPARSEMEM enabled? If that is the
> case why not optimize for it?

Because I tend to dislike micro-optimizations without performance
numbers for code that is not on a hot path. But I mean in this case, as
you said, you need the pfn either way, so it's completely fine with.

I do wonder, however, if you should just pass in the migratetype from
the caller. That would be even faster ;)

--
Thanks,

David / dhildenb