btrfs: cleanup 64bit/32bit divs, compile time constants

Switch to div_u64 if the divisor is a numeric constant or sum of
sizeof()s. We can remove a few instances of do_div that has the hidden
semtantics of changing the 1st argument.

Small power-of-two divisors are converted to bitshifts, large values are
kept intact for clarity.

Signed-off-by: David Sterba <dsterba@suse.cz>

fs/btrfs/dev-replace.c

@@ -670,8 +670,8 @@ void btrfs_dev_replace_status(struct btrfs_fs_info *fs_info,
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
 		srcdev = dev_replace->srcdev;
-		args->status.progress_1000 = div64_u64(dev_replace->cursor_left,
+		args->status.progress_1000 = div_u64(dev_replace->cursor_left,
-			div64_u64(btrfs_device_get_total_bytes(srcdev), 1000));
+			div_u64(btrfs_device_get_total_bytes(srcdev), 1000));
 		break;
 	}
 	btrfs_dev_replace_unlock(dev_replace);
@@ -806,7 +806,7 @@ static int btrfs_dev_replace_kthread(void *data)
 		btrfs_dev_replace_status(fs_info, status_args);
 		progress = status_args->status.progress_1000;
 		kfree(status_args);
-		do_div(progress, 10);
+		progress = div_u64(progress, 10);
 		printk_in_rcu(KERN_INFO
 			"BTRFS: continuing dev_replace from %s (devid %llu) to %s @%u%%\n",
 			dev_replace->srcdev->missing ? "<missing disk>" :

fs/btrfs/disk-io.c

@@ -2277,7 +2277,7 @@ int open_ctree(struct super_block *sb,
 	fs_info->free_chunk_space = 0;
 	fs_info->tree_mod_log = RB_ROOT;
 	fs_info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
-	fs_info->avg_delayed_ref_runtime = div64_u64(NSEC_PER_SEC, 64);
+	fs_info->avg_delayed_ref_runtime = NSEC_PER_SEC >> 6; /* div by 64 */
 	/* readahead state */
 	INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
 	spin_lock_init(&fs_info->reada_lock);

fs/btrfs/extent-tree.c

@@ -2561,8 +2561,7 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 		 */
 		spin_lock(&delayed_refs->lock);
 		avg = fs_info->avg_delayed_ref_runtime * 3 + runtime;
-		avg = div64_u64(avg, 4);
+		fs_info->avg_delayed_ref_runtime = avg >> 2;	/* div by 4 */
-		fs_info->avg_delayed_ref_runtime = avg;
 		spin_unlock(&delayed_refs->lock);
 	}
 	return 0;
@@ -2624,7 +2623,7 @@ static inline u64 heads_to_leaves(struct btrfs_root *root, u64 heads)
 	 * We don't ever fill up leaves all the way so multiply by 2 just to be
 	 * closer to what we're really going to want to ouse.
 	 */
-	return div64_u64(num_bytes, BTRFS_LEAF_DATA_SIZE(root));
+	return div_u64(num_bytes, BTRFS_LEAF_DATA_SIZE(root));
 }
 
 int btrfs_check_space_for_delayed_refs(struct btrfs_trans_handle *trans,
@@ -3193,7 +3192,7 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 	struct inode *inode = NULL;
 	u64 alloc_hint = 0;
 	int dcs = BTRFS_DC_ERROR;
-	int num_pages = 0;
+	u64 num_pages = 0;
 	int retries = 0;
 	int ret = 0;
 
@@ -3277,7 +3276,7 @@ again:
 	 * taking up quite a bit since it's not folded into the other space
 	 * cache.
 	 */
-	num_pages = (int)div64_u64(block_group->key.offset, 256 * 1024 * 1024);
+	num_pages = div_u64(block_group->key.offset, 256 * 1024 * 1024);
 	if (!num_pages)
 		num_pages = 1;
 
@@ -4770,10 +4769,10 @@ static u64 calc_global_metadata_size(struct btrfs_fs_info *fs_info)
 
 	num_bytes = (data_used >> fs_info->sb->s_blocksize_bits) *
 		    csum_size * 2;
-	num_bytes += div64_u64(data_used + meta_used, 50);
+	num_bytes += div_u64(data_used + meta_used, 50);
 
 	if (num_bytes * 3 > meta_used)
-		num_bytes = div64_u64(meta_used, 3);
+		num_bytes = div_u64(meta_used, 3);
 
 	return ALIGN(num_bytes, fs_info->extent_root->nodesize << 10);
 }
@@ -5039,7 +5038,7 @@ static u64 calc_csum_metadata_size(struct inode *inode, u64 num_bytes,
 	else
 		BTRFS_I(inode)->csum_bytes -= num_bytes;
 	csum_size = BTRFS_LEAF_DATA_SIZE(root) - sizeof(struct btrfs_item);
-	num_csums_per_leaf = (int)div64_u64(csum_size,
+	num_csums_per_leaf = (int)div_u64(csum_size,
 					    sizeof(struct btrfs_csum_item) +
 					    sizeof(struct btrfs_disk_key));
 	num_csums = (int)div64_u64(BTRFS_I(inode)->csum_bytes, root->sectorsize);

fs/btrfs/free-space-cache.c

@@ -1537,7 +1537,7 @@ static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
 		max_bytes = MAX_CACHE_BYTES_PER_GIG;
 	else
 		max_bytes = MAX_CACHE_BYTES_PER_GIG *
-			div64_u64(size, 1024 * 1024 * 1024);
+			div_u64(size, 1024 * 1024 * 1024);
 
 	/*
 	 * we want to account for 1 more bitmap than what we have so we can make
@@ -1552,14 +1552,14 @@ static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
 	}
 
 	/*
-	 * we want the extent entry threshold to always be at most 1/2 the maxw
+	 * we want the extent entry threshold to always be at most 1/2 the max
 	 * bytes we can have, or whatever is less than that.
 	 */
 	extent_bytes = max_bytes - bitmap_bytes;
-	extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));
+	extent_bytes = min_t(u64, extent_bytes, max_bytes >> 1);
 
 	ctl->extents_thresh =
-		div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
+		div_u64(extent_bytes, sizeof(struct btrfs_free_space));
 }
 
 static inline void __bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,

fs/btrfs/math.h

@@ -28,8 +28,7 @@ static inline u64 div_factor(u64 num, int factor)
 	if (factor == 10)
 		return num;
 	num *= factor;
-	do_div(num, 10);
+	return div_u64(num, 10);
-	return num;
 }
 
 static inline u64 div_factor_fine(u64 num, int factor)
@@ -37,8 +36,7 @@ static inline u64 div_factor_fine(u64 num, int factor)
 	if (factor == 100)
 		return num;
 	num *= factor;
-	do_div(num, 100);
+	return div_u64(num, 100);
-	return num;
 }
 
 #endif

fs/btrfs/super.c

@@ -1704,7 +1704,7 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
 		avail_space = device->total_bytes - device->bytes_used;
 
 		/* align with stripe_len */
-		do_div(avail_space, BTRFS_STRIPE_LEN);
+		avail_space = div_u64(avail_space, BTRFS_STRIPE_LEN);
 		avail_space *= BTRFS_STRIPE_LEN;
 
 		/*