From a8b3a677e786fa869d220a6a78b5532a36dc2f4d Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Wed, 2 Nov 2022 17:12:00 -0400 Subject: 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 --- fs/bcachefs/nocow_locking.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) create mode 100644 fs/bcachefs/nocow_locking.c (limited to 'fs/bcachefs/nocow_locking.c') diff --git a/fs/bcachefs/nocow_locking.c b/fs/bcachefs/nocow_locking.c new file mode 100644 index 000000000000..8f06e08370a2 --- /dev/null +++ b/fs/bcachefs/nocow_locking.c @@ -0,0 +1,15 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include "bcachefs.h" +#include "nocow_locking.h" +#include "util.h" + +void __bch2_bucket_nocow_lock(struct bucket_nocow_lock_table *t, + two_state_lock_t *l, int flags) +{ + struct bch_fs *c = container_of(t, struct bch_fs, nocow_locks); + u64 start_time = local_clock(); + + bch2_two_state_lock(l, flags & BUCKET_NOCOW_LOCK_UPDATE); + bch2_time_stats_update(&c->times[BCH_TIME_nocow_lock_contended], start_time); +} -- cgit