On Mon, Jan 27, 2025 at 05:20:25PM +0100, David Hildenbrand wrote: > > > 14.04% postgres [kernel.kallsyms] [k] try_grab_folio_fast > > > | > > > --14.04%--try_grab_folio_fast > > > gup_fast_fallback > > > | > > > --13.85%--iov_iter_extract_pages > > > bio_iov_iter_get_pages > > > iomap_dio_bio_iter > > > __iomap_dio_rw > > > iomap_dio_rw > > > xfs_file_dio_read > > > xfs_file_read_iter > > > __io_read > > > io_read > > > io_issue_sqe > > > io_submit_sqes > > > __do_sys_io_uring_enter > > > do_syscall_64 > > BTW, two things that come to mind: > > > (1) We always fallback to GUP-slow, I wonder why. GUP-fast would go via > try_grab_folio_fast(). I don't think we do? iov_iter_extract_pages() calls iov_iter_extract_user_pages() calls pin_user_pages_fast() calls gup_fast_fallback() calls gup_fast() calls gup_fast_pgd_range() calls gup_fast_p4d_range() calls gup_fast_pud_range() calls gup_fast_pud_leaf() calls try_grab_folio_fast() which is where we see the contention. If that were to fail, we'd see contention in __get_user_pages_locked(), right?
