26  *   1) space_info.  This is the ultimate arbiter of how much space we can use.
29  *   reservations we care about total_bytes - SUM(space_info->bytes_) when
34  *   metadata reservation we have.  You can see the comment in the block_rsv
38  *   3) btrfs_calc*_size.  These are the worst case calculations we used based
39  *   on the number of items we will want to modify.  We have one for changing
40  *   items, and one for inserting new items.  Generally we use these helpers to
46  *   We call into either btrfs_reserve_data_bytes() or
47  *   btrfs_reserve_metadata_bytes(), depending on which we're looking for, with
48  *   num_bytes we want to reserve.
65  *   Assume we are unable to simply make the reservation because we do not have
88  *     Check if ->bytes == 0, if it does we got our reservation and we can carry
89  *     on, if not return the appropriate error (ENOSPC, but can be EINTR if we
94  *   Same as the above, except we add ourselves to the
95  *   space_info->priority_tickets, and we do not use ticket->wait, we simply
101  *   Generally speaking we will have two cases for each state, a "nice" state
102  *   and a "ALL THE THINGS" state.  In btrfs we delay a lot of work in order to
106  *   reclaim space so we can make new reservations.
110  *     for example, we would update the inode item at write time to update the
112  *     isize or bytes.  We keep these delayed items to coalesce these operations
118  *     for delayed allocation.  We can reclaim some of this space simply by
119  *     running delalloc, but usually we need to wait for ordered extents to
123  *     We have a block reserve for the outstanding delayed refs space, and every
125  *     to reclaim space, but we want to hold this until the end because COW can
126  *     churn a lot and we can avoid making some extent tree modifications if we
130  *     We will skip this the first time through space reservation, because of
131  *     overcommit and we don't want to have a lot of useless metadata space when
135  *     If we're freeing inodes we're likely freeing checksums, file extent
140  *     This will commit the transaction.  Historically we had a lot of logic
141  *     surrounding whether or not we'd commit the transaction, but this waits born
142  *     out of a pre-tickets era where we could end up committing the transaction
144  *     ticketing system we know if we're not making progress and can error
150  *   Because we hold so many reservations for metadata we will allow you to
155  *   You can see the current logic for when we allow overcommit in
176  * after adding space to the filesystem, we need to clear the full flags
360 	 * If we have dup, raid1 or raid10 then only half of the free  in calc_available_free_space()
362 	 * doesn't include the parity drive, so we don't have to  in calc_available_free_space()
369 	 * If we aren't flushing all things, let us overcommit up to  in calc_available_free_space()
370 	 * 1/2th of the space. If we can flush, don't let us overcommit  in calc_available_free_space()
410  * This is for space we already have accounted in space_info->bytes_may_use, so
411  * basically when we're returning space from block_rsv's.
592 	/* Calc the number of the pages we need flush for space reservation */  in shrink_delalloc()
597 		 * to_reclaim is set to however much metadata we need to  in shrink_delalloc()
599 		 * exactly.  What we really want to do is reclaim full inode's  in shrink_delalloc()
601 		 * here.  We will take a fraction of the delalloc bytes for our  in shrink_delalloc()
603 		 * the amount we write to cover an entire dirty extent, which  in shrink_delalloc()
615 	 * If we are doing more ordered than delalloc we need to just wait on  in shrink_delalloc()
616 	 * ordered extents, otherwise we'll waste time trying to flush delalloc  in shrink_delalloc()
617 	 * that likely won't give us the space back we need.  in shrink_delalloc()
631 		 * We need to make sure any outstanding async pages are now  in shrink_delalloc()
632 		 * processed before we continue.  This is because things like  in shrink_delalloc()
634 		 * marked clean.  We don't use filemap_fwrite for flushing  in shrink_delalloc()
635 		 * because we want to control how many pages we write out at a  in shrink_delalloc()
636 		 * time, thus this is the only safe way to make sure we've  in shrink_delalloc()
640 		 * This exists because we do not want to wait for each  in shrink_delalloc()
641 		 * individual inode to finish its async work, we simply want to  in shrink_delalloc()
643 		 * for all of the async work to catch up.  Once we're done with  in shrink_delalloc()
644 		 * that we know we'll have ordered extents for everything and we  in shrink_delalloc()
645 		 * can decide if we wait for that or not.  in shrink_delalloc()
647 		 * If we choose to replace this in the future, make absolutely  in shrink_delalloc()
656 		 * We don't want to wait forever, if we wrote less pages in this  in shrink_delalloc()
657 		 * loop than we have outstanding, only wait for that number of  in shrink_delalloc()
658 		 * pages, otherwise we can wait for all async pages to finish  in shrink_delalloc()
679 		 * If we are for preemption we just want a one-shot of delalloc  in shrink_delalloc()
680 		 * flushing so we can stop flushing if we decide we don't need  in shrink_delalloc()
775 		 * If we have pending delayed iputs then we could free up a  in flush_space()
776 		 * bunch of pinned space, so make sure we run the iputs before  in flush_space()
777 		 * we do our pinned bytes check below.  in flush_space()
785 		 * We don't want to start a new transaction, just attach to the  in flush_space()
787 		 * happening at the moment. Note: we don't use a nostart join  in flush_space()
825 	 * We may be flushing because suddenly we have less space than we had  in btrfs_calc_reclaim_metadata_size()
826 	 * before, and now we're well over-committed based on our current free  in btrfs_calc_reclaim_metadata_size()
827 	 * space.  If that's the case add in our overage so we make sure to put  in btrfs_calc_reclaim_metadata_size()
848 	/* If we're just plain full then async reclaim just slows us down. */  in need_preemptive_reclaim()
860 	 * 128MiB is 1/4 of the maximum global rsv size.  If we have less than  in need_preemptive_reclaim()
862 	 * we don't have a lot of things that need flushing.  in need_preemptive_reclaim()
868 	 * We have tickets queued, bail so we don't compete with the async  in need_preemptive_reclaim()
875 	 * If we have over half of the free space occupied by reservations or  in need_preemptive_reclaim()
876 	 * pinned then we want to start flushing.  in need_preemptive_reclaim()
878 	 * We do not do the traditional thing here, which is to say  in need_preemptive_reclaim()
883 	 * because this doesn't quite work how we want.  If we had more than 50%  in need_preemptive_reclaim()
884 	 * of the space_info used by bytes_used and we had 0 available we'd just  in need_preemptive_reclaim()
885 	 * constantly run the background flusher.  Instead we want it to kick in  in need_preemptive_reclaim()
900 	 * much delalloc we need for the background flusher to kick in.  in need_preemptive_reclaim()
914 	 * If we have more ordered bytes than delalloc bytes then we're either  in need_preemptive_reclaim()
915 	 * doing a lot of DIO, or we simply don't have a lot of delalloc waiting  in need_preemptive_reclaim()
919 	 * nothing, if our reservations are tied up in ordered extents we'll  in need_preemptive_reclaim()
924 	 * block reserves that we would actually be able to directly reclaim  in need_preemptive_reclaim()
925 	 * from.  In this case if we're heavy on metadata operations this will  in need_preemptive_reclaim()
930 	 * We want to make sure we truly are maxed out on ordered however, so  in need_preemptive_reclaim()
931 	 * cut ordered in half, and if it's still higher than delalloc then we  in need_preemptive_reclaim()
932 	 * can keep flushing.  This is to avoid the case where we start  in need_preemptive_reclaim()
933 	 * flushing, and now delalloc == ordered and we stop preemptively  in need_preemptive_reclaim()
934 	 * flushing when we could still have several gigs of delalloc to flush.  in need_preemptive_reclaim()
980  * maybe_fail_all_tickets - we've exhausted our flushing, start failing tickets
982  * @space_info - the space info we were flushing
984  * We call this when we've exhausted our flushing ability and haven't made
986  * order, so if there is a large ticket first and then smaller ones we could
1028 		 * We're just throwing tickets away, so more flushing may not  in maybe_fail_all_tickets()
1029 		 * trip over btrfs_try_granting_tickets, so we need to call it  in maybe_fail_all_tickets()
1030 		 * here to see if we can make progress with the next ticket in  in maybe_fail_all_tickets()
1040  * This is for normal flushers, we can wait all goddamned day if we want to.  We
1041  * will loop and continuously try to flush as long as we are making progress.
1042  * We count progress as clearing off tickets each time we have to loop.
1087 		 * We do not want to empty the system of delalloc unless we're  in btrfs_async_reclaim_metadata_space()
1089 		 * logic before we start doing a FLUSH_DELALLOC_FULL.  in btrfs_async_reclaim_metadata_space()
1095 		 * We don't want to force a chunk allocation until we've tried  in btrfs_async_reclaim_metadata_space()
1096 		 * pretty hard to reclaim space.  Think of the case where we  in btrfs_async_reclaim_metadata_space()
1098 		 * to reclaim.  We would rather use that than possibly create a  in btrfs_async_reclaim_metadata_space()
1102 		 * around then we can force a chunk allocation.  in btrfs_async_reclaim_metadata_space()
1125  * This handles pre-flushing of metadata space before we get to the point that
1126  * we need to start blocking threads on tickets.  The logic here is different
1128  * much we need to flush, instead it attempts to keep us below the 80% full
1160 		 * We don't have a precise counter for the metadata being  in btrfs_preempt_reclaim_metadata_space()
1161 		 * reserved for delalloc, so we'll approximate it by subtracting  in btrfs_preempt_reclaim_metadata_space()
1163 		 * amount is higher than the individual reserves, then we can  in btrfs_preempt_reclaim_metadata_space()
1174 		 * We don't want to include the global_rsv in our calculation,  in btrfs_preempt_reclaim_metadata_space()
1175 		 * because that's space we can't touch.  Subtract it from the  in btrfs_preempt_reclaim_metadata_space()
1181 		 * We really want to avoid flushing delalloc too much, as it  in btrfs_preempt_reclaim_metadata_space()
1205 		 * We don't want to reclaim everything, just a portion, so scale  in btrfs_preempt_reclaim_metadata_space()
1217 	/* We only went through once, back off our clamping. */  in btrfs_preempt_reclaim_metadata_space()
1228  *   1) compression is on and we allocate less space than we reserved
1229  *   2) we are overwriting existing space
1236  *   For #2 this is trickier.  Once the ordered extent runs we will drop the
1237  *   extent in the range we are overwriting, which creates a delayed ref for
1242  *   If we are freeing inodes, we want to make sure all delayed iputs have
1249  *   This is where we reclaim all of the pinned space generated by running the
1253  *   For data we start with alloc chunk force, however we could have been full
1255  *   so if we now have space to allocate do the force chunk allocation.
1380 	 * because we may have only satisfied the priority tickets and still  in priority_reclaim_metadata_space()
1381 	 * left non priority tickets on the list.  We would then have  in priority_reclaim_metadata_space()
1402 	 * Attempt to steal from the global rsv if we can, except if the fs was  in priority_reclaim_metadata_space()
1405 	 * success to the caller if we can steal from the global rsv - this is  in priority_reclaim_metadata_space()
1418 	 * We must run try_granting_tickets here because we could be a large  in priority_reclaim_metadata_space()
1432 	/* We could have been granted before we got here. */  in priority_reclaim_data_space()
1467 			 * Delete us from the list. After we unlock the space  in wait_reserve_ticket()
1468 			 * info, we don't want the async reclaim job to reserve  in wait_reserve_ticket()
1496  * @flush:      how much we can flush
1536 	 * Check that we can't have an error set if the reservation succeeded,  in handle_reserve_ticket()
1564 	 * If we're heavy on ordered operations then clamping won't help us.  We  in maybe_clamp_preempt()
1568 	 * delayed nodes.  If we're already more ordered than delalloc then  in maybe_clamp_preempt()
1569 	 * we're keeping up, otherwise we aren't and should probably clamp.  in maybe_clamp_preempt()
1595  * @space_info: space info we want to allocate from
1596  * @orig_bytes: number of bytes we want
1597  * @flush:      whether or not we can flush to make our reservation
1621 	 * BTRFS_RESERVE_FLUSH_EVICT, as we could deadlock because those  in __reserve_bytes()
1640 	 * We don't want NO_FLUSH allocations to jump everybody, they can  in __reserve_bytes()
1651 	 * Carry on if we have enough space (short-circuit) OR call  in __reserve_bytes()
1652 	 * can_overcommit() to ensure we can overcommit to continue.  in __reserve_bytes()
1663 	 * Things are dire, we need to make a reservation so we don't abort.  We  in __reserve_bytes()
1664 	 * will let this reservation go through as long as we have actual space  in __reserve_bytes()
1677 	 * If we couldn't make a reservation then setup our reservation ticket  in __reserve_bytes()
1680 	 * If we are a priority flusher then we just need to add our ticket to  in __reserve_bytes()
1681 	 * the list and we will do our own flushing further down.  in __reserve_bytes()
1698 				 * We were forced to add a reserve ticket, so  in __reserve_bytes()
1719 		 * We will do the space reservation dance during log replay,  in __reserve_bytes()
1720 		 * which means we won't have fs_info->fs_root set, so don't do  in __reserve_bytes()
1721 		 * the async reclaim as we will panic.  in __reserve_bytes()
1744  * @block_rsv:  block_rsv we're allocating for
1745  * @orig_bytes: number of bytes we want
1746  * @flush:      whether or not we can flush to make our reservation
1779  * @bytes:   number of bytes we need
1780  * @flush:   how we are allowed to flush
1783  * space then we will attempt to flush space as specified by flush.
1806 /* Dump all the space infos when we abort a transaction due to ENOSPC. */
1830 	/* It's df, we don't care if it's racy */  in btrfs_account_ro_block_groups_free_space()