mm: move memcmp_pages() and pages_identical()

Patch series "THP aware uprobe", v13.

This patchset makes uprobe aware of THPs.

Currently, when uprobe is attached to text on THP, the page is split by
FOLL_SPLIT.  As a result, uprobe eliminates the performance benefit of
THP.

This set makes uprobe THP-aware.  Instead of FOLL_SPLIT, we introduces
FOLL_SPLIT_PMD, which only split PMD for uprobe.

After all uprobes within the THP are removed, the PTE-mapped pages are
regrouped as huge PMD.

This set (plus a few THP patches) is also available at

   https://github.com/liu-song-6/linux/tree/uprobe-thp

This patch (of 6):

Move memcmp_pages() to mm/util.c and pages_identical() to mm.h, so that we
can use them in other files.

Link: http://lkml.kernel.org/r/20190815164525.1848545-2-songliubraving@fb.com
Signed-off-by: Song Liu <songliubraving@fb.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <matthew.wilcox@oracle.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 20 insertions, 18 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 57a9fa34f159..0ac87d9ee9d8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2868,5 +2868,12 @@ void __init setup_nr_node_ids(void);
 static inline void setup_nr_node_ids(void) {}
 #endif
 
+extern int memcmp_pages(struct page *page1, struct page *page2);
+
+static inline int pages_identical(struct page *page1, struct page *page2)
+{
+        return !memcmp_pages(page1, page2);
+}
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */
diff --git a/mm/ksm.c b/mm/ksm.c
index 3dc4346411e4..dbee2eb4dd05 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1029,24 +1029,6 @@ static u32 calc_checksum(struct page *page)
         return checksum;
 }
 
-static int memcmp_pages(struct page *page1, struct page *page2)
-{
-        char *addr1, *addr2;
-        int ret;
-
-        addr1 = kmap_atomic(page1);
-        addr2 = kmap_atomic(page2);
-        ret = memcmp(addr1, addr2, PAGE_SIZE);
-        kunmap_atomic(addr2);
-        kunmap_atomic(addr1);
-        return ret;
-}
-
-static inline int pages_identical(struct page *page1, struct page *page2)
-{
-        return !memcmp_pages(page1, page2);
-}
-
 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
                               pte_t *orig_pte)
 {
diff --git a/mm/util.c b/mm/util.c
index bab284d69c8c..37f7b6711514 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -783,3 +783,16 @@ out_mm:
 out:
         return res;
 }
+
+int memcmp_pages(struct page *page1, struct page *page2)
+{
+        char *addr1, *addr2;
+        int ret;
+
+        addr1 = kmap_atomic(page1);
+        addr2 = kmap_atomic(page2);
+        ret = memcmp(addr1, addr2, PAGE_SIZE);
+        kunmap_atomic(addr2);
+        kunmap_atomic(addr1);
+        return ret;
+}