btrfs: simplify percent calculation helpers, rename div_factor

The div_factor* helpers calculate fraction or percentage fraction. The
name is a bit confusing, we use it only for percentage calculations and
there are two helpers.

There's a helper mult_frac that's for general fractions, that tries to
be accurate but we multiply and divide by small numbers so we can use
the div_u64 helper.

Rename the div_factor* helpers and use 1..100 percentage range, also drop
the case checking for percentage == 100, it's never hit.

The conversions:

* div_factor calculates tenths and the numbers need to be adjusted
* div_factor_fine is direct replacement
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1551,7 +1551,7 @@ static bool should_reclaim_block_group(struct btrfs_block_group *bg, u64 bytes_f
 	if (reclaim_thresh == 0)
 		return false;
 
-	thresh = div_factor_fine(bg->length, reclaim_thresh);
+	thresh = mult_perc(bg->length, reclaim_thresh);
 
 	/*
 	 * If we were below the threshold before don't reclaim, we are likely a
@@ -3523,13 +3523,13 @@ static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
 	 */
 	if (force == CHUNK_ALLOC_LIMITED) {
 		thresh = btrfs_super_total_bytes(fs_info->super_copy);
-		thresh = max_t(u64, SZ_64M, div_factor_fine(thresh, 1));
+		thresh = max_t(u64, SZ_64M, mult_perc(thresh, 1));
 
 		if (sinfo->total_bytes - bytes_used < thresh)
 			return 1;
 	}
 
-	if (bytes_used + SZ_2M < div_factor(sinfo->total_bytes, 8))
+	if (bytes_used + SZ_2M < mult_perc(sinfo->total_bytes, 80))
 		return 0;
 	return 1;
 }

fs/btrfs/block-rsv.c

@@ -227,7 +227,7 @@ int btrfs_block_rsv_add(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
-int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_factor)
+int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_percent)
 {
 	u64 num_bytes = 0;
 	int ret = -ENOSPC;
@@ -236,7 +236,7 @@ int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_factor)
 		return 0;
 
 	spin_lock(&block_rsv->lock);
-	num_bytes = div_factor(block_rsv->size, min_factor);
+	num_bytes = mult_perc(block_rsv->size, min_percent);
 	if (block_rsv->reserved >= num_bytes)
 		ret = 0;
 	spin_unlock(&block_rsv->lock);

fs/btrfs/block-rsv.h

@@ -63,7 +63,7 @@ void btrfs_free_block_rsv(struct btrfs_fs_info *fs_info,
 int btrfs_block_rsv_add(struct btrfs_fs_info *fs_info,
 			struct btrfs_block_rsv *block_rsv, u64 num_bytes,
 			enum btrfs_reserve_flush_enum flush);
-int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_factor);
+int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_percent);
 int btrfs_block_rsv_refill(struct btrfs_fs_info *fs_info,
 			   struct btrfs_block_rsv *block_rsv, u64 min_reserved,
 			   enum btrfs_reserve_flush_enum flush);

fs/btrfs/free-space-cache.c

@@ -2726,8 +2726,7 @@ static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
 		btrfs_mark_bg_unused(block_group);
 	} else if (bg_reclaim_threshold &&
 		   reclaimable_unusable >=
-		   div_factor_fine(block_group->zone_capacity,
-				   bg_reclaim_threshold)) {
+		   mult_perc(block_group->zone_capacity, bg_reclaim_threshold)) {
 		btrfs_mark_bg_to_reclaim(block_group);
 	}
 

fs/btrfs/misc.h

@@ -40,22 +40,10 @@ static inline void cond_wake_up_nomb(struct wait_queue_head *wq)
 		wake_up(wq);
 }
 
-static inline u64 div_factor(u64 num, int factor)
+static inline u64 mult_perc(u64 num, u32 percent)
 {
-	if (factor == 10)
-		return num;
-	num *= factor;
-	return div_u64(num, 10);
+	return div_u64(num * percent, 100);
 }
-
-static inline u64 div_factor_fine(u64 num, int factor)
-{
-	if (factor == 100)
-		return num;
-	num *= factor;
-	return div_u64(num, 100);
-}
-
 /* Copy of is_power_of_two that is 64bit safe */
 static inline bool is_power_of_two_u64(u64 n)
 {

fs/btrfs/space-info.c

@@ -859,7 +859,7 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
 	u64 thresh;
 	u64 used;
 
-	thresh = div_factor_fine(total, 90);
+	thresh = mult_perc(total, 90);
 
 	lockdep_assert_held(&space_info->lock);
 
@@ -977,7 +977,7 @@ static bool steal_from_global_rsv(struct btrfs_fs_info *fs_info,
 		return false;
 
 	spin_lock(&global_rsv->lock);
-	min_bytes = div_factor(global_rsv->size, 1);
+	min_bytes = mult_perc(global_rsv->size, 10);
 	if (global_rsv->reserved < min_bytes + ticket->bytes) {
 		spin_unlock(&global_rsv->lock);
 		return false;

fs/btrfs/sysfs.c

@@ -764,7 +764,7 @@ static ssize_t btrfs_chunk_size_store(struct kobject *kobj,
 	val = min(val, BTRFS_MAX_DATA_CHUNK_SIZE);
 
 	/* Limit stripe size to 10% of available space. */
-	val = min(div_factor(fs_info->fs_devices->total_rw_bytes, 1), val);
+	val = min(mult_perc(fs_info->fs_devices->total_rw_bytes, 10), val);
 
 	/* Must be multiple of 256M. */
 	val &= ~((u64)SZ_256M - 1);

fs/btrfs/transaction.c

@@ -949,7 +949,7 @@ static bool should_end_transaction(struct btrfs_trans_handle *trans)
 	if (btrfs_check_space_for_delayed_refs(fs_info))
 		return true;
 
-	return !!btrfs_block_rsv_check(&fs_info->global_block_rsv, 5);
+	return !!btrfs_block_rsv_check(&fs_info->global_block_rsv, 50);
 }
 
 bool btrfs_should_end_transaction(struct btrfs_trans_handle *trans)

fs/btrfs/volumes.c

@@ -3614,16 +3614,14 @@ static int chunk_usage_range_filter(struct btrfs_fs_info *fs_info, u64 chunk_off
 	if (bargs->usage_min == 0)
 		user_thresh_min = 0;
 	else
-		user_thresh_min = div_factor_fine(cache->length,
-						  bargs->usage_min);
+		user_thresh_min = mult_perc(cache->length, bargs->usage_min);
 
 	if (bargs->usage_max == 0)
 		user_thresh_max = 1;
 	else if (bargs->usage_max > 100)
 		user_thresh_max = cache->length;
 	else
-		user_thresh_max = div_factor_fine(cache->length,
-						  bargs->usage_max);
+		user_thresh_max = mult_perc(cache->length, bargs->usage_max);
 
 	if (user_thresh_min <= chunk_used && chunk_used < user_thresh_max)
 		ret = 0;
@@ -3647,7 +3645,7 @@ static int chunk_usage_filter(struct btrfs_fs_info *fs_info,
 	else if (bargs->usage > 100)
 		user_thresh = cache->length;
 	else
-		user_thresh = div_factor_fine(cache->length, bargs->usage);
+		user_thresh = mult_perc(cache->length, bargs->usage);
 
 	if (chunk_used < user_thresh)
 		ret = 0;
@@ -5113,7 +5111,7 @@ static void init_alloc_chunk_ctl_policy_regular(
 		ctl->devs_max = min_t(int, ctl->devs_max, BTRFS_MAX_DEVS_SYS_CHUNK);
 
 	/* We don't want a chunk larger than 10% of writable space */
-	ctl->max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
+	ctl->max_chunk_size = min(mult_perc(fs_devices->total_rw_bytes, 10),
 				  ctl->max_chunk_size);
 	ctl->dev_extent_min = BTRFS_STRIPE_LEN * ctl->dev_stripes;
 }
@@ -5144,7 +5142,7 @@ static void init_alloc_chunk_ctl_policy_zoned(
 	}
 
 	/* We don't want a chunk larger than 10% of writable space */
-	limit = max(round_down(div_factor(fs_devices->total_rw_bytes, 1),
+	limit = max(round_down(mult_perc(fs_devices->total_rw_bytes, 10),
 			       zone_size),
 		    min_chunk_size);
 	ctl->max_chunk_size = min(limit, ctl->max_chunk_size);