page_writeback: revive cancel_dirty_page() in a restricted form

cancel_dirty_page() had some issues and b9ea25152e56 ("page_writeback:
clean up mess around cancel_dirty_page()") replaced it with
account_page_cleaned() which makes the caller responsible for clearing
the dirty bit; unfortunately, the planned changes for cgroup writeback
support requires synchronization between dirty bit manipulation and
stat updates.  While we can open-code such synchronization in each
account_page_cleaned() callsite, that's gonna be unnecessarily awkward
and verbose.

This patch revives cancel_dirty_page() but in a more restricted form.
All it does is TestClearPageDirty() followed by account_page_cleaned()
invocation if the page was dirty.  This helper covers all
account_page_cleaned() usages except for __delete_from_page_cache()
which is a special case anyway and left alone.  As this leaves no
module user for account_page_cleaned(), EXPORT_SYMBOL() is dropped
from it.

This patch just revives cancel_dirty_page() as a trivial wrapper to
replace equivalent usages and doesn't introduce any functional
changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0755b9fd03a7..a83cf3a6f78e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1215,6 +1215,7 @@ void account_page_dirtied(struct page *page, struct address_space *mapping);
 void account_page_cleaned(struct page *page, struct address_space *mapping);
 int set_page_dirty(struct page *page);
 int set_page_dirty_lock(struct page *page);
+void cancel_dirty_page(struct page *page);
 int clear_page_dirty_for_io(struct page *page);
 
 int get_cmdline(struct task_struct *task, char *buffer, int buflen);