[v9,2/5] btrfs: space-info: Use per-profile available space in can_overcommit()
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Message ID 20200602090905.63899-3-wqu@suse.com
State New
Headers show
  • Introduce per-profile available space array to avoid over-confident can_overcommit()
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Commit Message

Qu Wenruo June 2, 2020, 9:09 a.m. UTC
For the following disk layout, can_overcommit() can cause false
confidence in available space:

  devid 1 unallocated:	1T
  devid 2 unallocated:	10T
  metadata type:	RAID1

As can_overcommit() simply uses unallocated space with factor to
calculate the allocatable metadata chunk size.

can_overcommit() believes we still have 5.5T for metadata chunks, while
the truth is, we only have 1T available for metadata chunks.
This can lead to ENOSPC at run_delalloc_range() and cause transaction

Since factor based calculation can't distinguish RAID1/RAID10 and DUP at
all, we need proper chunk-allocator level awareness to do such estimation.

Thankfully, we have per-profile available space already calculated, just
use that facility to avoid such false confidence.

Reported-by: Marc Lehmann <schmorp@schmorp.de>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
 fs/btrfs/space-info.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

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diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 41ee88633769..f3b4e14f3727 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -310,25 +310,21 @@  static u64 calc_available_free_space(struct btrfs_fs_info *fs_info,
 			  struct btrfs_space_info *space_info,
 			  enum btrfs_reserve_flush_enum flush)
+	enum btrfs_raid_types index;
 	u64 profile;
 	u64 avail;
-	int factor;
 	if (space_info->flags & BTRFS_BLOCK_GROUP_SYSTEM)
 		profile = btrfs_system_alloc_profile(fs_info);
 		profile = btrfs_metadata_alloc_profile(fs_info);
-	avail = atomic64_read(&fs_info->free_chunk_space);
-	 * If we have dup, raid1 or raid10 then only half of the free
-	 * space is actually usable.  For raid56, the space info used
-	 * doesn't include the parity drive, so we don't have to
-	 * change the math
+	 * Grab avail space from per-profile array which should be as accurate
+	 * as chunk allocator.
-	factor = btrfs_bg_type_to_factor(profile);
-	avail = div_u64(avail, factor);
+	index = btrfs_bg_flags_to_raid_index(profile);
+	avail = atomic64_read(&fs_info->fs_devices->per_profile_avail[index]);
 	 * If we aren't flushing all things, let us overcommit up to