btrfs: rename need_do_async_reclaim

All of our normal flushing is asynchronous reclaim, so this helper is
poorly named.  This is more checking if we need to preemptively flush
space, so rename it to need_preemptive_reclaim.

Also switch it to bool and make it plain static as followup patches will
move more code here.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/space-info.c

@@ -808,18 +808,18 @@ btrfs_calc_reclaim_metadata_size(struct btrfs_fs_info *fs_info,
 	return to_reclaim;
 }
 
-static inline int need_do_async_reclaim(struct btrfs_fs_info *fs_info,
-					struct btrfs_space_info *space_info,
-					u64 used)
+static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
+				    struct btrfs_space_info *space_info,
+				    u64 used)
 {
 	u64 thresh = div_factor_fine(space_info->total_bytes, 98);
 
 	/* If we're just plain full then async reclaim just slows us down. */
 	if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh)
-		return 0;
+		return false;
 
 	if (!btrfs_calc_reclaim_metadata_size(fs_info, space_info))
-		return 0;
+		return false;
 
 	return (used >= thresh && !btrfs_fs_closing(fs_info) &&
 		!test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
@@ -1028,7 +1028,7 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 
 	spin_lock(&space_info->lock);
 	used = btrfs_space_info_used(space_info, true);
-	while (need_do_async_reclaim(fs_info, space_info, used)) {
+	while (need_preemptive_reclaim(fs_info, space_info, used)) {
 		enum btrfs_flush_state flush;
 		u64 delalloc_size = 0;
 		u64 to_reclaim, block_rsv_size;
@@ -1508,7 +1508,7 @@ static int __reserve_bytes(struct btrfs_fs_info *fs_info,
 		 * the async reclaim as we will panic.
 		 */
 		if (!test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags) &&
-		    need_do_async_reclaim(fs_info, space_info, used) &&
+		    need_preemptive_reclaim(fs_info, space_info, used) &&
 		    !work_busy(&fs_info->preempt_reclaim_work)) {
 			trace_btrfs_trigger_flush(fs_info, space_info->flags,
 						  orig_bytes, flush, "preempt");