From 008cfe4418b3dbda2ff820cdd7b1a5ce458ae444 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Fri, 25 Sep 2020 18:25:57 -0400 Subject: mm: Introduce mm_struct.has_pinned (Commit message majorly collected from Jason Gunthorpe) Reduce the chance of false positive from page_maybe_dma_pinned() by keeping track if the mm_struct has ever been used with pin_user_pages(). This allows cases that might drive up the page ref_count to avoid any penalty from handling dma_pinned pages. Future work is planned, to provide a more sophisticated solution, likely to turn it into a real counter. For now, make it atomic_t but use it as a boolean for simplicity. Suggested-by: Jason Gunthorpe Signed-off-by: Peter Xu Signed-off-by: Linus Torvalds --- mm/gup.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'mm/gup.c') diff --git a/mm/gup.c b/mm/gup.c index 578bf5bd8bf8..dfe781d2ad4c 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1255,6 +1255,9 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, BUG_ON(*locked != 1); } + if (flags & FOLL_PIN) + atomic_set(¤t->mm->has_pinned, 1); + /* * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior * is to set FOLL_GET if the caller wants pages[] filled in (but has @@ -2660,6 +2663,9 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, FOLL_FAST_ONLY))) return -EINVAL; + if (gup_flags & FOLL_PIN) + atomic_set(¤t->mm->has_pinned, 1); + if (!(gup_flags & FOLL_FAST_ONLY)) might_lock_read(¤t->mm->mmap_lock); -- cgit v1.2.3