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authorIra Weiny <ira.weiny@intel.com>2021-02-10 07:22:14 +0100
committerDavid Sterba <dsterba@suse.com>2021-02-11 19:54:43 +0100
commitbb90d4bc7b6a536b2e4db45f4763e467c2008251 (patch)
tree7abfbdb2bf10ea31d480f143f3efccb4aa733966 /include
parentLinux 5.11-rc7 (diff)
downloadlinux-bb90d4bc7b6a536b2e4db45f4763e467c2008251.tar.xz
linux-bb90d4bc7b6a536b2e4db45f4763e467c2008251.zip
mm/highmem: Lift memcpy_[to|from]_page to core
Working through a conversion to a call kmap_local_page() instead of kmap() revealed many places where the pattern kmap/memcpy/kunmap occurred. Eric Biggers, Matthew Wilcox, Christoph Hellwig, Dan Williams, and Al Viro all suggested putting this code into helper functions. Al Viro further pointed out that these functions already existed in the iov_iter code.[1] Various locations for the lifted functions were considered. Headers like mm.h or string.h seem ok but don't really portray the functionality well. pagemap.h made some sense but is for page cache functionality.[2] Another alternative would be to create a new header for the promoted memcpy functions, but it masks the fact that these are designed to copy to/from pages using the kernel direct mappings and complicates matters with a new header. Placing these functions in 'highmem.h' is suboptimal especially with the changes being proposed in the functionality of kmap. From a caller perspective including/using 'highmem.h' implies that the functions defined in that header are only required when highmem is in use which is increasingly not the case with modern processors. However, highmem.h is where all the current functions like this reside (zero_user(), clear_highpage(), clear_user_highpage(), copy_user_highpage(), and copy_highpage()). So it makes the most sense even though it is distasteful for some.[3] Lift memcpy_to_page() and memcpy_from_page() to pagemap.h. [1] https://lore.kernel.org/lkml/20201013200149.GI3576660@ZenIV.linux.org.uk/ https://lore.kernel.org/lkml/20201013112544.GA5249@infradead.org/ [2] https://lore.kernel.org/lkml/20201208122316.GH7338@casper.infradead.org/ [3] https://lore.kernel.org/lkml/20201013200149.GI3576660@ZenIV.linux.org.uk/#t https://lore.kernel.org/lkml/20201208163814.GN1563847@iweiny-DESK2.sc.intel.com/ Cc: Boris Pismenny <borisp@mellanox.com> Cc: Or Gerlitz <gerlitz.or@gmail.com> Cc: Dave Hansen <dave.hansen@intel.com> Suggested-by: Matthew Wilcox <willy@infradead.org> Suggested-by: Christoph Hellwig <hch@infradead.org> Suggested-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Suggested-by: Eric Biggers <ebiggers@kernel.org> Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/highmem.h18
1 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index d2c70d3772a3..736b6a9f144d 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -276,4 +276,22 @@ static inline void copy_highpage(struct page *to, struct page *from)
#endif
+static inline void memcpy_from_page(char *to, struct page *page,
+ size_t offset, size_t len)
+{
+ char *from = kmap_atomic(page);
+
+ memcpy(to, from + offset, len);
+ kunmap_atomic(from);
+}
+
+static inline void memcpy_to_page(struct page *page, size_t offset,
+ const char *from, size_t len)
+{
+ char *to = kmap_atomic(page);
+
+ memcpy(to + offset, from, len);
+ kunmap_atomic(to);
+}
+
#endif /* _LINUX_HIGHMEM_H */