f2fs: restructure f2fs page.private layout

Restruct f2fs page private layout for below reasons:

There are some cases that f2fs wants to set a flag in a page to
indicate a specified status of page:
a) page is in transaction list for atomic write
b) page contains dummy data for aligned write
c) page is migrating for GC
d) page contains inline data for inline inode flush
e) page belongs to merkle tree, and is verified for fsverity
f) page is dirty and has filesystem/inode reference count for writeback
g) page is temporary and has decompress io context reference for compression

There are existed places in page structure we can use to store
f2fs private status/data:
- page.flags: PG_checked, PG_private
- page.private

However it was a mess when we using them, which may cause potential
confliction:
		page.private	PG_private	PG_checked	page._refcount (+1 at most)
a)		-1		set				+1
b)		-2		set
c), d), e)					set
f)		0		set				+1
g)		pointer		set

The other problem is page.flags has no free slot, if we can avoid set
zero to page.private and set PG_private flag, then we use non-zero value
to indicate PG_private status, so that we may have chance to reclaim
PG_private slot for other usage. [1]

The other concern is f2fs has bad scalability in aspect of indicating
more page status.

So in this patch, let's restructure f2fs' page.private as below to
solve above issues:

Layout A: lowest bit should be 1
| bit0 = 1 | bit1 | bit2 | ... | bit MAX | private data .... |
 bit 0	PAGE_PRIVATE_NOT_POINTER
 bit 1	PAGE_PRIVATE_ATOMIC_WRITE
 bit 2	PAGE_PRIVATE_DUMMY_WRITE
 bit 3	PAGE_PRIVATE_ONGOING_MIGRATION
 bit 4	PAGE_PRIVATE_INLINE_INODE
 bit 5	PAGE_PRIVATE_REF_RESOURCE
 bit 6-	f2fs private data

Layout B: lowest bit should be 0
 page.private is a wrapped pointer.

After the change:
		page.private	PG_private	PG_checked	page._refcount (+1 at most)
a)		11		set				+1
b)		101		set				+1
c)		1001		set				+1
d)		10001		set				+1
e)						set
f)		100001		set				+1
g)		pointer		set				+1

[1] https://lore.kernel.org/linux-f2fs-devel/20210422154705.GO3596236@casper.infradead.org/T/#u

Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 76 insertions, 22 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c83d90125ebd..f26a1c34102a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1291,17 +1291,85 @@ enum {
 				 */
 };
 
+static inline int f2fs_test_bit(unsigned int nr, char *addr);
+static inline void f2fs_set_bit(unsigned int nr, char *addr);
+static inline void f2fs_clear_bit(unsigned int nr, char *addr);
+
 /*
- * this value is set in page as a private data which indicate that
- * the page is atomically written, and it is in inmem_pages list.
+ * Layout of f2fs page.private:
+ *
+ * Layout A: lowest bit should be 1
+ * | bit0 = 1 | bit1 | bit2 | ... | bit MAX | private data .... |
+ * bit 0	PAGE_PRIVATE_NOT_POINTER
+ * bit 1	PAGE_PRIVATE_ATOMIC_WRITE
+ * bit 2	PAGE_PRIVATE_DUMMY_WRITE
+ * bit 3	PAGE_PRIVATE_ONGOING_MIGRATION
+ * bit 4	PAGE_PRIVATE_INLINE_INODE
+ * bit 5	PAGE_PRIVATE_REF_RESOURCE
+ * bit 6-	f2fs private data
+ *
+ * Layout B: lowest bit should be 0
+ * page.private is a wrapped pointer.
  */
-#define ATOMIC_WRITTEN_PAGE		((unsigned long)-1)
-#define DUMMY_WRITTEN_PAGE		((unsigned long)-2)
+enum {
+	PAGE_PRIVATE_NOT_POINTER,		/* private contains non-pointer data */
+	PAGE_PRIVATE_ATOMIC_WRITE,		/* data page from atomic write path */
+	PAGE_PRIVATE_DUMMY_WRITE,		/* data page for padding aligned IO */
+	PAGE_PRIVATE_ONGOING_MIGRATION,		/* data page which is on-going migrating */
+	PAGE_PRIVATE_INLINE_INODE,		/* inode page contains inline data */
+	PAGE_PRIVATE_REF_RESOURCE,		/* dirty page has referenced resources */
+	PAGE_PRIVATE_MAX
+};
+
+#define PAGE_PRIVATE_GET_FUNC(name, flagname) \
+static inline bool page_private_##name(struct page *page) \
+{ \
+	return test_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)) && \
+		test_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
+}
+
+#define PAGE_PRIVATE_SET_FUNC(name, flagname) \
+static inline void set_page_private_##name(struct page *page) \
+{ \
+	if (!PagePrivate(page)) { \
+		get_page(page); \
+		SetPagePrivate(page); \
+	} \
+	set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)); \
+	set_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
+}
 
-#define IS_ATOMIC_WRITTEN_PAGE(page)			\
-		(page_private(page) == ATOMIC_WRITTEN_PAGE)
-#define IS_DUMMY_WRITTEN_PAGE(page)			\
-		(page_private(page) == DUMMY_WRITTEN_PAGE)
+#define PAGE_PRIVATE_CLEAR_FUNC(name, flagname) \
+static inline void clear_page_private_##name(struct page *page) \
+{ \
+	clear_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
+	if (page_private(page) == 1 << PAGE_PRIVATE_NOT_POINTER) { \
+		set_page_private(page, 0); \
+		if (PagePrivate(page)) { \
+			ClearPagePrivate(page); \
+			put_page(page); \
+		}\
+	} \
+}
+
+PAGE_PRIVATE_GET_FUNC(nonpointer, NOT_POINTER);
+PAGE_PRIVATE_GET_FUNC(reference, REF_RESOURCE);
+PAGE_PRIVATE_GET_FUNC(inline, INLINE_INODE);
+PAGE_PRIVATE_GET_FUNC(gcing, ONGOING_MIGRATION);
+PAGE_PRIVATE_GET_FUNC(atomic, ATOMIC_WRITE);
+PAGE_PRIVATE_GET_FUNC(dummy, DUMMY_WRITE);
+
+PAGE_PRIVATE_SET_FUNC(reference, REF_RESOURCE);
+PAGE_PRIVATE_SET_FUNC(inline, INLINE_INODE);
+PAGE_PRIVATE_SET_FUNC(gcing, ONGOING_MIGRATION);
+PAGE_PRIVATE_SET_FUNC(atomic, ATOMIC_WRITE);
+PAGE_PRIVATE_SET_FUNC(dummy, DUMMY_WRITE);
+
+PAGE_PRIVATE_CLEAR_FUNC(reference, REF_RESOURCE);
+PAGE_PRIVATE_CLEAR_FUNC(inline, INLINE_INODE);
+PAGE_PRIVATE_CLEAR_FUNC(gcing, ONGOING_MIGRATION);
+PAGE_PRIVATE_CLEAR_FUNC(atomic, ATOMIC_WRITE);
+PAGE_PRIVATE_CLEAR_FUNC(dummy, DUMMY_WRITE);
 
 /* For compression */
 enum compress_algorithm_type {
@@ -3169,20 +3237,6 @@ static inline bool __is_valid_data_blkaddr(block_t blkaddr)
 	return true;
 }
 
-static inline void f2fs_set_page_private(struct page *page,
-						unsigned long data)
-{
-	if (PagePrivate(page))
-		return;
-
-	attach_page_private(page, (void *)data);
-}
-
-static inline void f2fs_clear_page_private(struct page *page)
-{
-	detach_page_private(page);
-}
-
 /*
  * file.c
  */