+/*
+ * This cancels just the dirty bit on the kernel page itself, it does NOT
+ * actually remove dirty bits on any mmap's that may be around. It also
+ * leaves the page tagged dirty, so any sync activity will still find it on
+ * the dirty lists, and in particular, clear_page_dirty_for_io() will still
+ * look at the dirty bits in the VM.
+ *
+ * Doing this should *normally* only ever be done when a page is truncated,
+ * and is not actually mapped anywhere at all. However, fs/buffer.c does
+ * this when it notices that somebody has cleaned out all the buffers on a
+ * page without actually doing it through the VM. Can you say "ext3 is
+ * horribly ugly"? Thought you could.
+ */
+void cancel_dirty_page(struct page *page)
+{
+ struct address_space *mapping = page_mapping(page);
+
+ if (mapping_cap_account_dirty(mapping)) {
+ struct mem_cgroup *memcg;
+
+ memcg = mem_cgroup_begin_page_stat(page);
+
+ if (TestClearPageDirty(page))
+ account_page_cleaned(page, mapping, memcg);
+
+ mem_cgroup_end_page_stat(memcg);
+ } else {
+ ClearPageDirty(page);
+ }
+}
+EXPORT_SYMBOL(cancel_dirty_page);
+