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Subject[PATCH v2 2/3] mm: introduce put_user_page[s](), placeholder versions
Date
From: John Hubbard <jhubbard@nvidia.com>

Introduces put_user_page(), which simply calls put_page().
This provides a way to update all get_user_pages*() callers,
so that they call put_user_page(), instead of put_page().

Also introduces put_user_pages(), and a few dirty/locked variations,
as a replacement for release_pages(), for the same reasons.
These may be used for subsequent performance improvements,
via batching of pages to be released.

This prepares for eventually fixing the problem described
in [1], and is following a plan listed in [2], [3], [4].

[1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()"

[2] https://lkml.kernel.org/r/20180709080554.21931-1-jhubbard@nvidia.com
Proposed steps for fixing get_user_pages() + DMA problems.

[3]https://lkml.kernel.org/r/20180710082100.mkdwngdv5kkrcz6n@quack2.suse.cz
Bounce buffers (otherwise [2] is not really viable).

[4] https://lkml.kernel.org/r/20181003162115.GG24030@quack2.suse.cz
Follow-up discussions.

CC: Matthew Wilcox <willy@infradead.org>
CC: Michal Hocko <mhocko@kernel.org>
CC: Christopher Lameter <cl@linux.com>
CC: Jason Gunthorpe <jgg@ziepe.ca>
CC: Dan Williams <dan.j.williams@intel.com>
CC: Jan Kara <jack@suse.cz>
CC: Al Viro <viro@zeniv.linux.org.uk>
CC: Jerome Glisse <jglisse@redhat.com>
CC: Christoph Hellwig <hch@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/mm.h | 42 ++++++++++++++++++++++++++++++++++++++++--
1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a61ebe8ad4ca..1a9aae7c659f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -137,6 +137,8 @@ extern int overcommit_ratio_handler(struct ctl_table *, int, void __user *,
size_t *, loff_t *);
extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
size_t *, loff_t *);
+int set_page_dirty(struct page *page);
+int set_page_dirty_lock(struct page *page);

#define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))

@@ -943,6 +945,44 @@ static inline void put_page(struct page *page)
__put_page(page);
}

+/* Placeholder version, until all get_user_pages*() callers are updated. */
+static inline void put_user_page(struct page *page)
+{
+ put_page(page);
+}
+
+/* For get_user_pages*()-pinned pages, use these variants instead of
+ * release_pages():
+ */
+static inline void put_user_pages_dirty(struct page **pages,
+ unsigned long npages)
+{
+ while (npages) {
+ set_page_dirty(pages[npages]);
+ put_user_page(pages[npages]);
+ --npages;
+ }
+}
+
+static inline void put_user_pages_dirty_lock(struct page **pages,
+ unsigned long npages)
+{
+ while (npages) {
+ set_page_dirty_lock(pages[npages]);
+ put_user_page(pages[npages]);
+ --npages;
+ }
+}
+
+static inline void put_user_pages(struct page **pages,
+ unsigned long npages)
+{
+ while (npages) {
+ put_user_page(pages[npages]);
+ --npages;
+ }
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
@@ -1534,8 +1574,6 @@ int redirty_page_for_writepage(struct writeback_control *wbc,
void account_page_dirtied(struct page *page, struct address_space *mapping);
void account_page_cleaned(struct page *page, struct address_space *mapping,
struct bdi_writeback *wb);
-int set_page_dirty(struct page *page);
-int set_page_dirty_lock(struct page *page);
void __cancel_dirty_page(struct page *page);
static inline void cancel_dirty_page(struct page *page)
{
--
2.19.0
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