[PATCH 1/6] mm/gup: introduce pin_user_page()
From: John Hubbard <jhubbard@nvidia.com>
Date: 2022-08-27 08:36:22
Also in:
linux-fsdevel, linux-mm, linux-nfs, linux-xfs, lkml
Subsystem:
memory management, memory management - core, memory management - gup (get user pages), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
pin_user_page() is an externally-usable version of try_grab_page(), but with semantics that match get_page(), so that it can act as a drop-in replacement for get_page(). Specifically, pin_user_page() has a void return type. pin_user_page() elevates a page's refcount using FOLL_PIN rules. This means that the caller must release the page via unpin_user_page(). Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- include/linux/mm.h | 1 + mm/gup.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 34 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 982f2607180b..85a105157334 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -1869,6 +1869,7 @@ long pin_user_pages_remote(struct mm_struct *mm, long get_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas); +void pin_user_page(struct page *page); long pin_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas);
diff --git a/mm/gup.c b/mm/gup.c
index 5abdaf487460..245ccb41ed8c 100644
--- a/mm/gup.c
+++ b/mm/gup.c@@ -3213,6 +3213,39 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages, } EXPORT_SYMBOL(pin_user_pages); +/** + * pin_user_page() - apply a FOLL_PIN reference to a page + * + * @page: the page to be pinned. + * + * This is similar to get_user_pages(), except that the page's refcount is + * elevated using FOLL_PIN, instead of FOLL_GET. + * + * IMPORTANT: The caller must release the page via unpin_user_page(). + * + */ +void pin_user_page(struct page *page) +{ + struct folio *folio = page_folio(page); + + WARN_ON_ONCE(folio_ref_count(folio) <= 0); + + /* + * Similar to try_grab_page(): be sure to *also* + * increment the normal page refcount field at least once, + * so that the page really is pinned. + */ + if (folio_test_large(folio)) { + folio_ref_add(folio, 1); + atomic_add(1, folio_pincount_ptr(folio)); + } else { + folio_ref_add(folio, GUP_PIN_COUNTING_BIAS); + } + + node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1); +} +EXPORT_SYMBOL(pin_user_page); + /* * pin_user_pages_unlocked() is the FOLL_PIN variant of * get_user_pages_unlocked(). Behavior is the same, except that this one sets
--
2.37.2