Re: Prerequisites for Large Anon Folios

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

On 31/08/2023 01:08, Yin, Fengwei wrote:
> 
> On 8/30/2023 6:44 PM, Ryan Roberts wrote:
>> Hi All,
>>
>>
>> I want to get serious about getting large anon folios merged. To do that, there
>> are a number of outstanding prerequistes. I'm hoping the respective owners may
>> be able to provide an update on progress?
>>
>> I appreciate everyone is busy and likely juggling multiple things, so understand
>> if no progress has been made or likely to be made - it would be good to know
>> that though, so I can attempt to make alternative plans.
>>
>> See questions/comments below.
>>
>> Thanks!
>>
>>
...
>>
>>>
>>> - item:
>>>     mlock
>>>
>>>   priority:
>>>     prerequisite
>>>
>>>   description: >-
>>>     Large, pte-mapped folios are ignored when mlock is requested. Code comment
>>>     for mlock_vma_folio() says "...filter out pte mappings of THPs, which cannot
>>>     be consistently counted: a pte mapping of the THP head cannot be
>>>     distinguished by the page alone."
>>>
>>>   location:
>>>     - mlock_pte_range()
>>>     - mlock_vma_folio()
>>>
>>>   links:
>>>     - https://lore.kernel.org/linux-mm/20230712060144.3006358-1-fengwei.yin@intel.com/
>>>
>>>   assignee:
>>>     Yin, Fengwei <fengwei.yin@intel.com>
>>>
>>>
>>
>> series on list at [2]. Does this series cover everything?
> Yes. I suppose so. I already collected comment from you. And I am waiting for review comment
> from Yu who is on vacation now. Then, I will work on v3.

Great -thanks for the fast reply!

> 
>>
>> [2] https://lore.kernel.org/linux-mm/20230809061105.3369958-1-fengwei.yin@intel.com/
>>
>>
>>>
>>> - item:
>>>     madvise
>>>
>>>   priority:
>>>     prerequisite
>>>
>>>   description: >-
>>>     MADV_COLD, MADV_PAGEOUT, MADV_FREE: For large folios, code assumes exclusive
>>>     only if mapcount==1, else skips remainder of operation. For large,
>>>     pte-mapped folios, exclusive folios can have mapcount upto nr_pages and
>>>     still be exclusive. Even better; don't split the folio if it fits entirely
>>>     within the range. Likely depends on "shared vs exclusive mappings".
>>>
>>>   links:
>>>     - https://lore.kernel.org/linux-mm/20230713150558.200545-1-fengwei.yin@intel.com/
>>>
>>>   location:
>>>     - madvise_cold_or_pageout_pte_range()
>>>     - madvise_free_pte_range()
>>>
>>>   assignee:
>>>     Yin, Fengwei <fengwei.yin@intel.com>
>>
>> As I understand it: initial solution based on folio_estimated_sharers() has gone
>> into v6.5. Have a dependecy on David's precise shared vs exclusive work for an
>> improved solution. And I think you mentioned you are planning to do a change
>> that avoids splitting a large folio if it is entirely covered by the range?
> The changes based on folio_estimated_sharers() is in. Once David's solution is
> ready, will switch to new solution.
> 
> For avoids splitting large folio, it was in the patchset I posted (before split
> folio_estimated_sharers() part out).

The RFC version? Do you plan to post an updated version, or are you waiting for
David's shared vs exclusive series before moving forwards?

> 
> Regards
> Yin, Fengwei