linux-kernel - [PATCH 0/8] Snapshot deletion improvements

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Message-ID: <20250502200002.1309862-1-kent.overstreet@linux.dev>
Date: Fri,  2 May 2025 15:59:52 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 0/8] Snapshot deletion improvements

Snapshot deletion performance has been reported to be an issue, so this
patch series should address that.

The important optimization relies on the fact that if an
extent/dirent/xattr exists, a version of that inode must exist in that
specific snapshot. We can make use of that to avoid a lot of scanning.

Previously only fsck relied on this, so it would spit out a warning and
correct the issue in its in memory data structures if this occurred.
Now, it's turned into a proper fsck_err() with on-disk repair if
detected.

We also want some additional safety with this: if snapshot deletion ever
screws up and doesn't delete all the keys it was supposed to, we want to
be able to automatically repair.

So there's a new on disk format version with an incompatible (i.e. must
be expliticly enabled) feature, where we never delete snapshot keys - we
just mark them as deleted.

This allows fsck to differentiate between "key for deleted snapshot, I
know how to repair this" vs. "key for missing snapshot, we're not sure
what happened and someone should probably take a look".

And snapshot deletion status is now present in sysfs, currently with
btree and position in that btree. We do have per-snapshot-id accounting,
so it might be possible to turn that into a proper progress indicator
later.

Kent Overstreet (8):
  bcachefs: snapshot delete progress indicator
  bcachefs: Add comments for inode snapshot requirements
  bcachefs: kill inode_walker_entry.snapshot
  bcachefs: BCH_FSCK_ERR_snapshot_key_missing_inode_snapshot
  bcachefs: Skip unrelated snapshot trees in snapshot deletion
  bcachefs: BCH_SNAPSHOT_DELETED -> BCH_SNAPSHOT_WILL_DELETE
  bcachefs: bcachefs_metadata_version_snapshot_deletion_v2
  bcachefs: delete_dead_snapshot_keys_v2()

 fs/bcachefs/bcachefs.h         |   3 +-
 fs/bcachefs/bcachefs_format.h  |   3 +-
 fs/bcachefs/fsck.c             |  78 ++++---
 fs/bcachefs/io_write.c         |   6 +
 fs/bcachefs/sb-errors_format.h |   4 +-
 fs/bcachefs/snapshot.c         | 389 +++++++++++++++++++++++++--------
 fs/bcachefs/snapshot.h         |  32 ++-
 fs/bcachefs/snapshot_format.h  |   4 +-
 fs/bcachefs/snapshot_types.h   |  56 +++++
 fs/bcachefs/subvolume.c        |   2 -
 fs/bcachefs/subvolume.h        |   3 -
 fs/bcachefs/subvolume_types.h  |  27 ---
 fs/bcachefs/super.c            |   1 +
 fs/bcachefs/sysfs.c            |   5 +
 fs/bcachefs/xattr.c            |   5 +
 15 files changed, 445 insertions(+), 173 deletions(-)
 create mode 100644 fs/bcachefs/snapshot_types.h

-- 
2.49.0