Re: Allow migration of mlocked page?

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> Okay. Let's summary opinions in this thread until now.
>
> 1. mlock doesn't have pinning's semantic by definition of opengroup.
> 2. man page says "No page fault". It's bad. Maybe need fix up of man page.

Yes, it should be.

> 3. Thera are several places which already have migrate mlocked pages but it's okay because
>   it's done under user's control while compaction/khugepagd doesn't.

I disagree. CPUSETS are used from admins. realtime _application_ is written
by application developers. ok, they are often overwrapped or the same. but it's
not exactly true. memory hotplug has similar situation.

Moreover, Think mix up rt-app and non-rt-migrate_pages-user-app situation. RT
app still be faced minor page fault and it's not expected from rt-app
developers.


> 3. Many application already used mlock by semantic of 2. So let's break legacy application if possible.

Many? really? I guess it's a very few.

> 4. CMA consider getting of free contiguos memory as top priority so latency may be okay in CMA
>   while THP consider latency as top priority.
> 5. Let's define new API which would be
>   5.1 mlock(SOFT) - it can gaurantee memory-resident.
>   5.2 mlock(HARD) - it can gaurantee 1 and pinning.
>   Current mlock could be 5.1, then we should implement 5.2. Or
>   Current mlock could be 5.2, then we should implement 5.1
>   We can implement it by PG_pinned or vma flags.

I definitely agree we need both pinned and not-pinned mlock.


> One of clear point is that it's okay to migrate mlocked page in CMA.
> And we can migrate mlocked anonymous pages and mlocked file pages by MIGRATE_ASYNC mode in compaction
> if we all agree Peter who says "mlocked mean NO MAJOR FAULT".

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