On Sat, 27 Aug 2022 01:36:03 -0700 John Hubbard <jhubbard@xxxxxxxxxx> wrote: > Background: The Direct IO part of the block infrastructure is being > changed to use pin_user_page*() and unpin_user_page*() calls, in place > of a mix of get_user_pages_fast(), get_page(), and put_page(). These > have to be changed over all at the same time, for block, bio, and all > filesystems. However, most filesystems can be changed via iomap and core > filesystem routines, so let's get that in place, and then continue on > with converting the remaining filesystems (9P, CIFS) and anything else > that feeds pages into bio that ultimately get released via > bio_release_pages(). > > Add a new config parameter, CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO, and > dio_w_*() wrapper functions. The dio_w_ prefix was chosen for > uniqueness, so as to ease a subsequent kernel-wide rename via > search-and-replace. Together, these allow the developer to choose > between these sets of routines, for Direct IO code paths: > > a) pin_user_pages_fast() > pin_user_page() > unpin_user_page() > > b) get_user_pages_fast() > get_page() > put_page() > > CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO is a temporary setting, and may > be deleted once the conversion is complete. In the meantime, developers > can enable this in order to try out each filesystem. > > Please remember that these /proc/vmstat items (below) should normally > contain the same values as each other, except during the middle of > pin/unpin operations. As such, they can be helpful when monitoring test > runs: > > nr_foll_pin_acquired > nr_foll_pin_released > > ... > > +static inline void dio_w_unpin_user_pages(struct page **pages, > + unsigned long npages) > +{ > + unsigned long i; > + > + for (i = 0; i < npages; i++) > + put_page(pages[i]); > +} release_pages()? Might be faster if many of the pages are page_count()==1. (release_pages() was almost as simple as the above when I added it a million years ago. But then progress happened).