page_writeback: clean up mess around cancel_dirty_page()

This patch replaces cancel_dirty_page() with a helper function
account_page_cleaned() which only updates counters.  It's called from
truncate_complete_page() and from try_to_free_buffers() (hack for ext3).
Page is locked in both cases, page-lock protects against concurrent
dirtiers: see commit 2d6d7f982846 ("mm: protect set_page_dirty() from
ongoing truncation").

Delete_from_page_cache() shouldn't be called for dirty pages, they must
be handled by caller (either written or truncated).  This patch treats
final dirty accounting fixup at the end of __delete_from_page_cache() as
a debug check and adds WARN_ON_ONCE() around it.  If something removes
dirty pages without proper handling that might be a bug and unwritten
data might be lost.

Hugetlbfs has no dirty pages accounting, ClearPageDirty() is enough
here.

cancel_dirty_page() in nfs_wb_page_cancel() is redundant.  This is
helper for nfs_invalidate_page() and it's called only in case complete
invalidation.

The mess was started in v2.6.20 after commits 46d2277c796f ("Clean up
and make try_to_free_buffers() not race with dirty pages") and
3e67c0987d75 ("truncate: clear page dirtiness before running
try_to_free_buffers()") first was reverted right in v2.6.20 in commit
ecdfc9787fe5 ("Resurrect 'try_to_free_buffers()' VM hackery"), second in
v2.6.25 commit a2b345642f53 ("Fix dirty page accounting leak with ext3
data=journal").

Custom fixes were introduced between these points.  NFS in v2.6.23, commit
1b3b4a1a2deb ("NFS: Fix a write request leak in nfs_invalidate_page()").
Kludge in __delete_from_page_cache() in v2.6.24, commit 3a6927906f1b ("Do
dirty page accounting when removing a page from the page cache").  Since
v2.6.25 all of them are redundant.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 3 insertions, 8 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 20805db..c7a5602 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3243,8 +3243,8 @@ int try_to_free_buffers(struct page *page)
 	 * to synchronise against __set_page_dirty_buffers and prevent the
 	 * dirty bit from being lost.
 	 */
-	if (ret)
-		cancel_dirty_page(page, PAGE_CACHE_SIZE);
+	if (ret && TestClearPageDirty(page))
+		account_page_cleaned(page, mapping);
 	spin_unlock(&mapping->private_lock);
 out:
 	if (buffers_to_free) {
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index c274aca..db76cec 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -319,7 +319,7 @@ static int hugetlbfs_write_end(struct file *file, struct address_space *mapping,
 
 static void truncate_huge_page(struct page *page)
 {
-	cancel_dirty_page(page, /* No IO accounting for huge pages? */0);
+	ClearPageDirty(page);
 	ClearPageUptodate(page);
 	delete_from_page_cache(page);
 }
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 849ed78..7599310 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1876,11 +1876,6 @@ int nfs_wb_page_cancel(struct inode *inode, struct page *page)
 		 * request from the inode / page_private pointer and
 		 * release it */
 		nfs_inode_remove_request(req);
-		/*
-		 * In case nfs_inode_remove_request has marked the
-		 * page as being dirty
-		 */
-		cancel_dirty_page(page, PAGE_CACHE_SIZE);
 		nfs_unlock_and_release_request(req);
 	}