f2fs: compress: remove unneeded preallocation

We will reserve iblocks for compression saved, so during compressed
cluster overwrite, we don't need to preallocate blocks for later
write.

In addition, it adds a bug_on to detect wrong reserved iblock number
in __f2fs_cluster_blocks().

Bug fix in the original patch by Jaegeuk:
If we released compressed blocks having an immutable bit, we can see less
number of compressed block addresses. Let's fix wrong BUG_ON.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -926,6 +926,9 @@ static int __f2fs_cluster_blocks(struct inode *inode,
 					ret++;
 			}
 		}
+
+		f2fs_bug_on(F2FS_I_SB(inode),
+			!compr && ret != cluster_size && !IS_IMMUTABLE(inode));
 	}
 fail:
 	f2fs_put_dnode(&dn);
@@ -984,21 +987,16 @@ static int prepare_compress_overwrite(struct compress_ctx *cc,
 	struct f2fs_sb_info *sbi = F2FS_I_SB(cc->inode);
 	struct address_space *mapping = cc->inode->i_mapping;
 	struct page *page;
-	struct dnode_of_data dn;
 	sector_t last_block_in_bio;
 	unsigned fgp_flag = FGP_LOCK | FGP_WRITE | FGP_CREAT;
 	pgoff_t start_idx = start_idx_of_cluster(cc);
 	int i, ret;
-	bool prealloc;
 
 retry:
 	ret = f2fs_is_compressed_cluster(cc->inode, start_idx);
 	if (ret <= 0)
 		return ret;
 
-	/* compressed case */
-	prealloc = (ret < cc->cluster_size);
-
 	ret = f2fs_init_compress_ctx(cc);
 	if (ret)
 		return ret;
@@ -1056,25 +1054,6 @@ static int prepare_compress_overwrite(struct compress_ctx *cc,
 		}
 	}
 
-	if (prealloc) {
-		f2fs_do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, true);
-
-		set_new_dnode(&dn, cc->inode, NULL, NULL, 0);
-
-		for (i = cc->cluster_size - 1; i > 0; i--) {
-			ret = f2fs_get_block(&dn, start_idx + i);
-			if (ret) {
-				i = cc->cluster_size;
-				break;
-			}
-
-			if (dn.data_blkaddr != NEW_ADDR)
-				break;
-		}
-
-		f2fs_do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, false);
-	}
-
 	if (likely(!ret)) {
 		*fsdata = cc->rpages;
 		*pagep = cc->rpages[offset_in_cluster(cc, index)];

fs/f2fs/file.c

@@ -85,10 +85,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 			err = ret;
 			goto err;
 		} else if (ret) {
-			if (ret < F2FS_I(inode)->i_cluster_size) {
-				err = -EAGAIN;
-				goto err;
-			}
 			need_alloc = false;
 		}
 	}