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bcachefs: Add a comment for BTREE_INSERT_NOJOURNAL usage 

BTREE_INSERT_NOJOURNAL is primarily used for a performance optimization
related to inode updates and fsync - document it.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-11-04 13:49:31 -04:00
parent d3c7727bb9
commit 9fcdd23b6e
4 changed files with 14 additions and 4 deletions
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2
fs/bcachefs/btree_iter.c
View File

@ -257,7 +257,7 @@ static void bch2_btree_iter_verify(struct btree_iter *iter)
BUG_ON(!(iter->flags & __BTREE_ITER_ALL_SNAPSHOTS) &&
(iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
!btree_type_has_snapshots(iter->btree_id));
!btree_type_has_snapshot_field(iter->btree_id));
if (iter->update_path)
bch2_btree_path_verify(trans, iter->update_path);

3
fs/bcachefs/btree_iter.h
View File

@ -416,8 +416,7 @@ static inline unsigned __bch2_btree_iter_flags(struct btree_trans *trans,
flags |= BTREE_ITER_IS_EXTENTS;
if (!(flags & __BTREE_ITER_ALL_SNAPSHOTS) &&
!btree_type_has_snapshot_field(btree_id) &&
!btree_type_has_snapshots(btree_id))
!btree_type_has_snapshot_field(btree_id))
flags &= ~BTREE_ITER_ALL_SNAPSHOTS;
if (!(flags & BTREE_ITER_ALL_SNAPSHOTS) &&

2
fs/bcachefs/btree_types.h
View File

@ -713,7 +713,7 @@ static inline bool btree_type_has_snapshots(enum btree_id id)
static inline bool btree_type_has_snapshot_field(enum btree_id id)
{
const unsigned mask = 0
#define x(name, nr, flags, ...) |((!!((flags) & BTREE_ID_SNAPSHOT_FIELD)) << nr)
#define x(name, nr, flags, ...) |((!!((flags) & (BTREE_ID_SNAPSHOT_FIELD|BTREE_ID_SNAPSHOTS))) << nr)
BCH_BTREE_IDS()
#undef x
;

11
fs/bcachefs/io_write.c
View File

@ -202,6 +202,17 @@ static inline int bch2_extent_update_i_size_sectors(struct btree_trans *trans,
struct btree_iter iter;
struct bkey_i *k;
struct bkey_i_inode_v3 *inode;
/*
* Crazy performance optimization:
* Every extent update needs to also update the inode: the inode trigger
* will set bi->journal_seq to the journal sequence number of this
* transaction - for fsync.
*
* But if that's the only reason we're updating the inode (we're not
* updating bi_size or bi_sectors), then we don't need the inode update
* to be journalled - if we crash, the bi_journal_seq update will be
* lost, but that's fine.
*/
unsigned inode_update_flags = BTREE_UPDATE_NOJOURNAL;
int ret;