fs/btrfs/space-info.c

108  *   reclaim space so we can make new reservations.
115  *     into a single operation done on demand.  These are an easy way to reclaim
120  *     for delayed allocation.  We can reclaim some of this space simply by
122  *     reclaim the bulk of this space.
127  *     to reclaim space, but we want to hold this until the end because COW can
200  * scheduled for background reclaim.
483 	 * less pressure for the async metadata reclaim process, and it
696 		 * reclaim, but reclaiming that much data doesn't really track
697 		 * exactly.  What we really want to do is reclaim full inode's
702 		 * will reclaim the metadata reservation for that range.  If
940 	/* If we're just plain full then async reclaim just slows us down. */
1016 	 * block reserves that we would actually be able to directly reclaim
1186 		 * pretty hard to reclaim space.  Think of the case where we
1188 		 * to reclaim.  We would rather use that than possibly create a
1314 		 * We don't want to reclaim everything, just a portion, so scale
1316 		 * reclaim 1 items worth.
1358  *   This is where we reclaim all of the pinned space generated by running the
1504 	 * This is the priority reclaim path, so to_reclaim could be >0 still
1592 			 * info, we don't want the async reclaim job to reserve
1843 		 * the async reclaim as we will panic.
1996  * utilization when near full, and not do too much reclaim while
2008  * The fundamental goal of automatic reclaim is to protect the filesystem's
2013  * automatic reclaim must also back off as that space runs low. There is no
2017  * Furthermore, we want to avoid doing too much reclaim even if there are good
2019  * holes with writes. So we want to do just enough reclaim to try and stay
2022  * Therefore, the dynamic reclaim threshold is calculated as follows:
2024  * - ratchet up the intensity of reclaim depending on how far we are from
2059  * Under "urgent" reclaim, we will reclaim even fresh block groups that have
2060  * recently seen successful allocations, as we are desperate to reclaim
2088 		bool reclaim = false;
2095 			reclaim = true;
2099 		if (reclaim)
2105 	 * In situations where we are very motivated to reclaim (low unalloc)
2106 	 * use two passes to make the reclaim mark check best effort.