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Message-ID: <Zd4Ef49kHX3g69VT@bfoster>
Date: Tue, 27 Feb 2024 10:49:19 -0500
From: Brian Foster <bfoster@...hat.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
djwong@...nel.org
Subject: Re: [PATCH 01/21] bcachefs: KEY_TYPE_accounting
On Sat, Feb 24, 2024 at 09:38:03PM -0500, Kent Overstreet wrote:
> New key type for the disk space accounting rewrite.
>
> - Holds a variable sized array of u64s (may be more than one for
> accounting e.g. compressed and uncompressed size, or buckets and
> sectors for a given data type)
>
> - Updates are deltas, not new versions of the key: this means updates
> to accounting can happen via the btree write buffer, which we'll be
> teaching to accumulate deltas.
>
> Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
> ---
> fs/bcachefs/Makefile | 3 +-
> fs/bcachefs/bcachefs.h | 1 +
> fs/bcachefs/bcachefs_format.h | 80 +++------------
> fs/bcachefs/bkey_methods.c | 1 +
> fs/bcachefs/disk_accounting.c | 70 ++++++++++++++
> fs/bcachefs/disk_accounting.h | 52 ++++++++++
> fs/bcachefs/disk_accounting_format.h | 139 +++++++++++++++++++++++++++
> fs/bcachefs/replicas_format.h | 21 ++++
> fs/bcachefs/sb-downgrade.c | 12 ++-
> fs/bcachefs/sb-errors_types.h | 3 +-
> 10 files changed, 311 insertions(+), 71 deletions(-)
> create mode 100644 fs/bcachefs/disk_accounting.c
> create mode 100644 fs/bcachefs/disk_accounting.h
> create mode 100644 fs/bcachefs/disk_accounting_format.h
> create mode 100644 fs/bcachefs/replicas_format.h
>
..
> diff --git a/fs/bcachefs/disk_accounting_format.h b/fs/bcachefs/disk_accounting_format.h
> new file mode 100644
> index 000000000000..e06a42f0d578
> --- /dev/null
> +++ b/fs/bcachefs/disk_accounting_format.h
> @@ -0,0 +1,139 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _BCACHEFS_DISK_ACCOUNTING_FORMAT_H
> +#define _BCACHEFS_DISK_ACCOUNTING_FORMAT_H
> +
> +#include "replicas_format.h"
> +
> +/*
> + * Disk accounting - KEY_TYPE_accounting - on disk format:
> + *
> + * Here, the key has considerably more structure than a typical key (bpos); an
> + * accounting key is 'struct disk_accounting_key', which is a union of bpos.
> + *
First impression.. I'm a little confused why the key type is a union of
bpos. I'm possibly missing something fundamental/obvious, but could you
elaborate more on why that is here?
Brian
> + * This is a type-tagged union of all our various subtypes; a disk accounting
> + * key can be device counters, replicas counters, et cetera - it's extensible.
> + *
> + * The value is a list of u64s or s64s; the number of counters is specific to a
> + * given accounting type.
> + *
> + * Unlike with other key types, updates are _deltas_, and the deltas are not
> + * resolved until the update to the underlying btree, done by btree write buffer
> + * flush or journal replay.
> + *
> + * Journal replay in particular requires special handling. The journal tracks a
> + * range of entries which may possibly have not yet been applied to the btree
> + * yet - it does not know definitively whether individual entries are dirty and
> + * still need to be applied.
> + *
> + * To handle this, we use the version field of struct bkey, and give every
> + * accounting update a unique version number - a total ordering in time; the
> + * version number is derived from the key's position in the journal. Then
> + * journal replay can compare the version number of the key from the journal
> + * with the version number of the key in the btree to determine if a key needs
> + * to be replayed.
> + *
> + * For this to work, we must maintain this strict time ordering of updates as
> + * they are flushed to the btree, both via write buffer flush and via journal
> + * replay. This has complications for the write buffer code while journal replay
> + * is still in progress; the write buffer cannot flush any accounting keys to
> + * the btree until journal replay has finished replaying its accounting keys, or
> + * the (newer) version number of the keys from the write buffer will cause
> + * updates from journal replay to be lost.
> + */
> +
> +struct bch_accounting {
> + struct bch_val v;
> + __u64 d[];
> +};
> +
> +#define BCH_ACCOUNTING_MAX_COUNTERS 3
> +
> +#define BCH_DATA_TYPES() \
> + x(free, 0) \
> + x(sb, 1) \
> + x(journal, 2) \
> + x(btree, 3) \
> + x(user, 4) \
> + x(cached, 5) \
> + x(parity, 6) \
> + x(stripe, 7) \
> + x(need_gc_gens, 8) \
> + x(need_discard, 9)
> +
> +enum bch_data_type {
> +#define x(t, n) BCH_DATA_##t,
> + BCH_DATA_TYPES()
> +#undef x
> + BCH_DATA_NR
> +};
> +
> +static inline bool data_type_is_empty(enum bch_data_type type)
> +{
> + switch (type) {
> + case BCH_DATA_free:
> + case BCH_DATA_need_gc_gens:
> + case BCH_DATA_need_discard:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> +static inline bool data_type_is_hidden(enum bch_data_type type)
> +{
> + switch (type) {
> + case BCH_DATA_sb:
> + case BCH_DATA_journal:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> +#define BCH_DISK_ACCOUNTING_TYPES() \
> + x(nr_inodes, 0) \
> + x(persistent_reserved, 1) \
> + x(replicas, 2) \
> + x(dev_data_type, 3) \
> + x(dev_stripe_buckets, 4)
> +
> +enum disk_accounting_type {
> +#define x(f, nr) BCH_DISK_ACCOUNTING_##f = nr,
> + BCH_DISK_ACCOUNTING_TYPES()
> +#undef x
> + BCH_DISK_ACCOUNTING_TYPE_NR,
> +};
> +
> +struct bch_nr_inodes {
> +};
> +
> +struct bch_persistent_reserved {
> + __u8 nr_replicas;
> +};
> +
> +struct bch_dev_data_type {
> + __u8 dev;
> + __u8 data_type;
> +};
> +
> +struct bch_dev_stripe_buckets {
> + __u8 dev;
> +};
> +
> +struct disk_accounting_key {
> + union {
> + struct {
> + __u8 type;
> + union {
> + struct bch_nr_inodes nr_inodes;
> + struct bch_persistent_reserved persistent_reserved;
> + struct bch_replicas_entry_v1 replicas;
> + struct bch_dev_data_type dev_data_type;
> + struct bch_dev_stripe_buckets dev_stripe_buckets;
> + };
> + };
> + struct bpos _pad;
> + };
> +};
> +
> +#endif /* _BCACHEFS_DISK_ACCOUNTING_FORMAT_H */
> diff --git a/fs/bcachefs/replicas_format.h b/fs/bcachefs/replicas_format.h
> new file mode 100644
> index 000000000000..ed94f8c636b3
> --- /dev/null
> +++ b/fs/bcachefs/replicas_format.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _BCACHEFS_REPLICAS_FORMAT_H
> +#define _BCACHEFS_REPLICAS_FORMAT_H
> +
> +struct bch_replicas_entry_v0 {
> + __u8 data_type;
> + __u8 nr_devs;
> + __u8 devs[];
> +} __packed;
> +
> +struct bch_replicas_entry_v1 {
> + __u8 data_type;
> + __u8 nr_devs;
> + __u8 nr_required;
> + __u8 devs[];
> +} __packed;
> +
> +#define replicas_entry_bytes(_i) \
> + (offsetof(typeof(*(_i)), devs) + (_i)->nr_devs)
> +
> +#endif /* _BCACHEFS_REPLICAS_FORMAT_H */
> diff --git a/fs/bcachefs/sb-downgrade.c b/fs/bcachefs/sb-downgrade.c
> index 3337419faeff..33db8d7ca8c4 100644
> --- a/fs/bcachefs/sb-downgrade.c
> +++ b/fs/bcachefs/sb-downgrade.c
> @@ -52,9 +52,15 @@
> BCH_FSCK_ERR_subvol_fs_path_parent_wrong) \
> x(btree_subvolume_children, \
> BIT_ULL(BCH_RECOVERY_PASS_check_subvols), \
> - BCH_FSCK_ERR_subvol_children_not_set)
> + BCH_FSCK_ERR_subvol_children_not_set) \
> + x(disk_accounting_v2, \
> + BIT_ULL(BCH_RECOVERY_PASS_check_allocations), \
> + BCH_FSCK_ERR_accounting_mismatch)
>
> -#define DOWNGRADE_TABLE()
> +#define DOWNGRADE_TABLE() \
> + x(disk_accounting_v2, \
> + BIT_ULL(BCH_RECOVERY_PASS_check_alloc_info), \
> + BCH_FSCK_ERR_dev_usage_buckets_wrong)
>
> struct upgrade_downgrade_entry {
> u64 recovery_passes;
> @@ -108,7 +114,7 @@ void bch2_sb_set_upgrade(struct bch_fs *c,
> }
> }
>
> -#define x(ver, passes, ...) static const u16 downgrade_ver_##errors[] = { __VA_ARGS__ };
> +#define x(ver, passes, ...) static const u16 downgrade_##ver##_errors[] = { __VA_ARGS__ };
> DOWNGRADE_TABLE()
> #undef x
>
> diff --git a/fs/bcachefs/sb-errors_types.h b/fs/bcachefs/sb-errors_types.h
> index 0df4b0e7071a..383e13711001 100644
> --- a/fs/bcachefs/sb-errors_types.h
> +++ b/fs/bcachefs/sb-errors_types.h
> @@ -264,7 +264,8 @@
> x(subvol_children_not_set, 256) \
> x(subvol_children_bad, 257) \
> x(subvol_loop, 258) \
> - x(subvol_unreachable, 259)
> + x(subvol_unreachable, 259) \
> + x(accounting_mismatch, 260)
>
> enum bch_sb_error_id {
> #define x(t, n) BCH_FSCK_ERR_##t = n,
> --
> 2.43.0
>
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