Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[David Rientjes]

On Sun, 3 Nov 2019, John Hubbard wrote:

> Introduce pin_user_pages*() variations of get_user_pages*() calls,
> and also pin_longterm_pages*() variations.
> 
> These variants all set FOLL_PIN, which is also introduced, and
> thoroughly documented.
> 
> The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> to FOLL_PIN:
> 
>     pin_user_pages()
>     pin_user_pages_remote()
>     pin_user_pages_fast()
> 
>     pin_longterm_pages()
>     pin_longterm_pages_remote()
>     pin_longterm_pages_fast()
> 
> All pages that are pinned via the above calls, must be unpinned via
> put_user_page().
> 

Hi John,

I'm curious what consideration is given to what pageblock migrate types 
that FOLL_PIN and FOLL_LONGTERM pages originate from, assuming that 
longterm would want to originate from MIGRATE_UNMOVABLE pageblocks for the 
purposes of anti-fragmentation?