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author | Kent Overstreet <kent.overstreet@linux.dev> | 2022-11-02 17:12:00 -0400 |
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committer | Kent Overstreet <kent.overstreet@linux.dev> | 2023-10-22 17:09:51 -0400 |
commit | a8b3a677e786fa869d220a6a78b5532a36dc2f4d (patch) | |
tree | 3fdbdbb71945ae42dab8dc94971e1c78286eaa63 /fs/bcachefs/nocow_locking.h | |
parent | 4dcd1cae72912ab08d313ee5a730608022b211d4 (diff) | |
download | linux-a8b3a677e786fa869d220a6a78b5532a36dc2f4d.tar.gz linux-a8b3a677e786fa869d220a6a78b5532a36dc2f4d.tar.bz2 linux-a8b3a677e786fa869d220a6a78b5532a36dc2f4d.zip |
bcachefs: Nocow support
This adds support for nocow mode, where we do writes in-place when
possible. Patch components:
- New boolean filesystem and inode option, nocow: note that when nocow
is enabled, data checksumming and compression are implicitly disabled
- To prevent in-place writes from racing with data moves
(data_update.c) or bucket reuse (i.e. a bucket being reused and
re-allocated while a nocow write is in flight, we have a new locking
mechanism.
Buckets can be locked for either data update or data move, using a
fixed size hash table of two_state_shared locks. We don't have any
chaining, meaning updates and moves to different buckets that hash to
the same lock will wait unnecessarily - we'll want to watch for this
becoming an issue.
- The allocator path also needs to check for in-place writes in flight
to a given bucket before giving it out: thus we add another counter
to bucket_alloc_state so we can track this.
- Fsync now may need to issue cache flushes to block devices instead of
flushing the journal. We add a device bitmask to bch_inode_info,
ei_devs_need_flush, which tracks devices that need to have flushes
issued - note that this will lead to unnecessary flushes when other
codepaths have already issued flushes, we may want to replace this with
a sequence number.
- New nocow write path: look up extents, and if they're writable write
to them - otherwise fall back to the normal COW write path.
XXX: switch to sequence numbers instead of bitmask for devs needing
journal flush
XXX: ei_quota_lock being a mutex means bch2_nocow_write_done() needs to
run in process context - see if we can improve this
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Diffstat (limited to 'fs/bcachefs/nocow_locking.h')
-rw-r--r-- | fs/bcachefs/nocow_locking.h | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/fs/bcachefs/nocow_locking.h b/fs/bcachefs/nocow_locking.h new file mode 100644 index 000000000000..2a7a9f44e88e --- /dev/null +++ b/fs/bcachefs/nocow_locking.h @@ -0,0 +1,55 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _BCACHEFS_NOCOW_LOCKING_H +#define _BCACHEFS_NOCOW_LOCKING_H + +#include "bcachefs_format.h" +#include "two_state_shared_lock.h" + +#include <linux/hash.h> + +#define BUCKET_NOCOW_LOCKS_BITS 10 +#define BUCKET_NOCOW_LOCKS (1U << BUCKET_NOCOW_LOCKS_BITS) + +struct bucket_nocow_lock_table { + two_state_lock_t l[BUCKET_NOCOW_LOCKS]; +}; + +#define BUCKET_NOCOW_LOCK_UPDATE (1 << 0) + +static inline two_state_lock_t *bucket_nocow_lock(struct bucket_nocow_lock_table *t, + struct bpos bucket) +{ + u64 dev_bucket = bucket.inode << 56 | bucket.offset; + unsigned h = hash_64(dev_bucket, BUCKET_NOCOW_LOCKS_BITS); + + return t->l + (h & (BUCKET_NOCOW_LOCKS - 1)); +} + +static inline bool bch2_bucket_nocow_is_locked(struct bucket_nocow_lock_table *t, + struct bpos bucket) +{ + two_state_lock_t *l = bucket_nocow_lock(t, bucket); + + return atomic_long_read(&l->v) != 0; +} + +static inline void bch2_bucket_nocow_unlock(struct bucket_nocow_lock_table *t, + struct bpos bucket, int flags) +{ + two_state_lock_t *l = bucket_nocow_lock(t, bucket); + + bch2_two_state_unlock(l, flags & BUCKET_NOCOW_LOCK_UPDATE); +} + +void __bch2_bucket_nocow_lock(struct bucket_nocow_lock_table *, two_state_lock_t *, int); + +static inline void bch2_bucket_nocow_lock(struct bucket_nocow_lock_table *t, + struct bpos bucket, int flags) +{ + two_state_lock_t *l = bucket_nocow_lock(t, bucket); + + if (!bch2_two_state_trylock(l, flags & BUCKET_NOCOW_LOCK_UPDATE)) + __bch2_bucket_nocow_lock(t, l, flags); +} + +#endif /* _BCACHEFS_NOCOW_LOCKING_H */ |