Re: ANON_LARGE_FOLIOS meeting follow-up & refined proposal

[Ryan Roberts <ryan.roberts@arm.com>]

On 02/10/2023 13:58, David Hildenbrand wrote:
>> [...]
>>
>> My concern is that the "fresh start" is not as simple as it appears. I've come
>> to the conclusion that if we have a new interface, then it should really be a
>> strict superset of THP to make it extensible in future. But that opens questions
> 
> ^ +1
> 
>> about how you configure PMD-sized allocations when both interfaces disagree. For
>> "enabled" its fairly straightforward; you can do a logical OR. But its less
>> clear how to handle disagreement over defrag. And then you have huge_zero_page
>> and khugepaged etc, which might just stay with THP. But eventually we will
> 
> Probably we want everything that THP had (khugepaged, zeropage, ...) also on
> some (selected?) smaller orders.
> 
>> probably want to do async collapse for smaller order folios too, and at that
>> point you have to duplicate all those controls... So I concluded that actually
>> it is cleaner to just bolt on a small-order extension to THP. I've updated all
>> the docs, and that was pretty simple to do, which usually suggests that the
>> extension is purely additive and shouldn't be confusing.
> 
> Fine with me. I don't quite like bitmaps exposed to user space, though. Just
> having a user-readable list or a "directory" with various options as files might
> be cleaner ...
> 
>>
>> Take a look at the patches, then make a judgement ;-)
>>
> 
> ... but we'll discuss it there :)
> 

David, FYI, the patches are posted at [1] (you're cc'ed) and have been in
mm-unstable for nearly a week - so I guess they will go to mm-stable soon by
default. So if you want to object to any of it, now's the time ;-).

[1] https://lore.kernel.org/linux-mm/20230929114421.3761121-1-ryan.roberts@arm.com/