f2fs: support POSIX_FADV_DONTNEED drop compressed page cache

Previously, compressed page cache drop when clean page cache, but
POSIX_FADV_DONTNEED can't clean compressed page cache because raw page
don't have private data, and won't call f2fs_invalidate_compress_pages.
This commit call f2fs_invalidate_compress_pages() directly in
f2fs_file_fadvise() for POSIX_FADV_DONTNEED case.

Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -4663,12 +4663,12 @@ out:
 static int f2fs_file_fadvise(struct file *filp, loff_t offset, loff_t len,
 		int advice)
 {
-	struct inode *inode;
 	struct address_space *mapping;
 	struct backing_dev_info *bdi;
+	struct inode *inode = file_inode(filp);
+	int err;
 
 	if (advice == POSIX_FADV_SEQUENTIAL) {
-		inode = file_inode(filp);
 		if (S_ISFIFO(inode->i_mode))
 			return -ESPIPE;
 
@@ -4685,7 +4685,13 @@ static int f2fs_file_fadvise(struct file *filp, loff_t offset, loff_t len,
 		return 0;
 	}
 
-	return generic_fadvise(filp, offset, len, advice);
+	err = generic_fadvise(filp, offset, len, advice);
+	if (!err && advice == POSIX_FADV_DONTNEED &&
+		test_opt(F2FS_I_SB(inode), COMPRESS_CACHE) &&
+		f2fs_compressed_file(inode))
+		f2fs_invalidate_compress_pages(F2FS_I_SB(inode), inode->i_ino);
+
+	return err;
 }
 
 #ifdef CONFIG_COMPAT