Re: [DISCUSSION] proposed mctl() API

[David Hildenbrand <david@redhat.com>]

On 04.06.25 14:00, Johannes Weiner wrote:
> On Fri, May 30, 2025 at 07:52:28PM +1200, Barry Song wrote:
>> On Fri, May 30, 2025 at 9:14 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>>>
>>> On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
>>>> Barry's problem is that we're all nervous about possibly regressing
>>>> performance on some unknown workloads.  Just try Barry's proposal, see
>>>> if anyone actually compains or if we're just afraid of our own shadows.
>>>
>>> I actually explained why I think this is a terrible idea. But okay, I
>>> tried the patch anyway.
>>>
>>> This is 'git log' on a hot kernel repo after a large IO stream:
>>>
>>>                                       VANILLA                      BARRY
>>> Real time                 49.93 (    +0.00%)         60.36 (   +20.48%)
>>> User time                 32.10 (    +0.00%)         32.09 (    -0.04%)
>>> System time               14.41 (    +0.00%)         14.64 (    +1.50%)
>>> pgmajfault              9227.00 (    +0.00%)      18390.00 (   +99.30%)
>>> workingset_refault_file  184.00 (    +0.00%)    236899.00 (+127954.05%)
>>>
>>> Clearly we can't generally ignore page cache hits just because the
>>> mmaps() are intermittent.
>>
>> Hi Johannes,
>> Thanks!
>>
>> Are you on v1, which lacks folio demotion[1], or v2, which includes it [2]?
>>
>> [1] https://lore.kernel.org/linux-mm/20250412085852.48524-1-21cnbao@gmail.com/
>> [2] https://lore.kernel.org/linux-mm/20250514070820.51793-1-21cnbao@gmail.com/
> 
> The subthread is about whether the reference dismissal / demotion
> should be unconditional (v1) or opt-in (v2).
> 
> I'm arguing for v2.

+1

-- 
Cheers,

David / dhildenb