The patch titled
Subject: mm/gup: introduce pin_user_page()
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-introduce-pin_user_page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-introduce-pin_user_page.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: mm/gup: introduce pin_user_page()
Date: Tue, 30 Aug 2022 21:18:38 -0700
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().
Link: https://lkml.kernel.org/r/20220831041843.973026-3-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Anna Schumaker <anna@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 1
mm/gup.c | 50 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+)
--- a/include/linux/mm.h~mm-gup-introduce-pin_user_page
+++ a/include/linux/mm.h
@@ -1943,6 +1943,7 @@ long pin_user_pages_remote(struct mm_str
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);
--- a/mm/gup.c~mm-gup-introduce-pin_user_page
+++ a/mm/gup.c
@@ -3240,6 +3240,56 @@ long pin_user_pages(unsigned long start,
}
EXPORT_SYMBOL(pin_user_pages);
+/**
+ * pin_user_page() - apply a FOLL_PIN reference to a file-backed page that the
+ * caller already owns.
+ *
+ * @page: the page to be pinned.
+ *
+ * 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().
+ *
+ * pin_user_page() is intended as a drop-in replacement for get_page(). This
+ * provides a way for callers to do a subsequent unpin_user_page() on the
+ * affected page. However, it is only intended for use by callers (file systems,
+ * block/bio) that have a file-backed page. Anonymous pages are not expected nor
+ * supported, and will generate a warning.
+ *
+ * pin_user_page() may also be thought of as 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().
+ *
+ * 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);
+
+ /*
+ * This function is only intended for file-backed callers, who already
+ * have a page reference.
+ */
+ WARN_ON_ONCE(PageAnon(page));
+
+ /*
+ * 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
_
Patches currently in -mm which might be from jhubbard@xxxxxxxxxx are
mm-change-release_pages-to-use-unsigned-long-for-npages.patch
mm-gup-introduce-pin_user_page.patch
block-add-dio_w_-wrappers-for-pin-unpin-user-pages.patch
iov_iter-new-iov_iter_pin_pages-routines.patch
block-bio-fs-convert-most-filesystems-to-pin_user_pages_fast.patch
nfs-direct-io-convert-to-foll_pin-pages.patch
fuse-convert-direct-io-paths-to-use-foll_pin.patch
