[PATCH v4 18/18] f2fs: make compressed files compatible with large folio

[Nanzhe Zhao <nzzhao.sigma@gmail.com>]

From: Nanzhe Zhao <zhaonanzhe@xiaomi.com>

The compression flag is the hint indicates that the inode can be
compressed, when the inode is using large folio, we expected it keeps
using the large folio read/write paths and its data stays uncompressed
on disk until the inode is evicted and re-read

Let f2fs_write_begin() skip the compression overwrite preparation for
such inodes and remove the compressed-file gate in
f2fs_read_data_large_folio() so the data is simply read/written as
regular blocks.

For the same reason, reject F2FS_IOC_COMPRESS_FILE with -EOPNOTSUPP
once the inode mapping is switched to large folios.

Signed-off-by: Nanzhe Zhao <zhaonanzhe@xiaomi.com>
---
 Documentation/filesystems/f2fs.rst | 10 ++++++++++
 fs/f2fs/compress.c                 |  2 ++
 fs/f2fs/data.c                     |  9 ++-------
 fs/f2fs/file.c                     |  7 +++++++
 4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index 771216f45..b4f436ffd 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -941,6 +941,16 @@ Compression implementation
   reserved via ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or the file size is
   truncated to zero.
 
+- Compression and large folios are not effective at the same time on a file:
+  a compressed inode does not use large folios, while an inode which is
+  using large folios keeps its data uncompressed on disk.  If the compression
+  flag is set on an inode that is already using large folios, the flag works
+  as a hint until the inode is evicted: the inode keeps using the large folio
+  read/write paths, f2fs_write_begin() skips the compression overwrite
+  preparation, and ioctl(F2FS_IOC_COMPRESS_FILE) fails with -EOPNOTSUPP.
+  Once the inode is evicted and read back, it uses order-0 folios again and
+  compression is applied as usual.
+
 Compress metadata layout::
 
 				[Dnode Structure]
diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 3d26bdd4d..f9839e2e0 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -78,6 +78,8 @@ bool f2fs_is_compressed_page(struct folio *folio)
 		return false;
 	if (folio_test_f2fs_nonpointer(folio))
 		return false;
+	if (f2fs_folio_has_ffs(folio))
+		return false;
 
 	f2fs_bug_on(F2FS_F_SB(folio),
 		*((u32 *)folio->private) != F2FS_COMPRESSED_PAGE_MAGIC);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 0e139b4ca..3647d5e97 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3243,12 +3243,6 @@ static int f2fs_read_data_large_folio(struct inode *inode,
 	int ret = 0;
 	bool folio_in_bio = false;
 
-	if (f2fs_compressed_file(inode)) {
-		if (folio)
-			folio_unlock(folio);
-		return -EOPNOTSUPP;
-	}
-
 	map.m_seg_type = NO_CHECK_TYPE;
 
 	if (rac)
@@ -5202,7 +5196,8 @@ static int f2fs_write_begin(const struct kiocb *iocb,
 	}
 
 #ifdef CONFIG_F2FS_FS_COMPRESSION
-	if (f2fs_compressed_file(inode)) {
+	if (f2fs_compressed_file(inode) &&
+	    !mapping_large_folio_support(inode->i_mapping)) {
 		int ret;
 		struct page *page;
 
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 9cee36258..6cd8df7a4 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -5024,6 +5024,13 @@ static int f2fs_ioc_compress_file(struct file *filp)
 	if (!(filp->f_mode & FMODE_WRITE))
 		return -EBADF;
 
+	/*
+	 * The mapping is already using large folios, where the data is kept
+	 * uncompressed, so refuse to start compressing the file.
+	 */
+	if (mapping_large_folio_support(inode->i_mapping))
+		return -EOPNOTSUPP;
+
 	f2fs_balance_fs(sbi, true);
 
 	ret = mnt_want_write_file(filp);
-- 
2.43.0