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

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?