Hi Steven, Thank you for your review, and I apologize for my delayed response.
---- On Wed, 18 Mar 2026 00:21:29 +0800 Steven Rostedt <[email protected]> wrote --- > On Tue, 17 Mar 2026 16:46:21 +0800 > Li Chen <[email protected]> wrote: > > > Commit-time fast commit snapshots run under jbd2_journal_lock_updates(), > > so it is useful to quantify the time spent with updates locked and to > > understand why snapshotting can fail. > > > > Add a new tracepoint, ext4_fc_lock_updates, reporting the time spent in > > the updates-locked window along with the number of snapshotted inodes > > and ranges. Record the first snapshot failure reason in a stable snap_err > > field for tooling. > > > > Signed-off-by: Li Chen <[email protected]> > > --- > > fs/ext4/ext4.h | 15 ++++++++ > > fs/ext4/fast_commit.c | 71 +++++++++++++++++++++++++++++-------- > > include/trace/events/ext4.h | 61 +++++++++++++++++++++++++++++++ > > 3 files changed, 132 insertions(+), 15 deletions(-) > > > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > > index 68a64fa0be926..b9e146f3dd9e4 100644 > > --- a/fs/ext4/ext4.h > > +++ b/fs/ext4/ext4.h > > @@ -1037,6 +1037,21 @@ enum { > > > > struct ext4_fc_inode_snap; > > > > +/* > > + * Snapshot failure reasons for ext4_fc_lock_updates tracepoint. > > + * Keep these stable for tooling. > > + */ > > +enum ext4_fc_snap_err { > > + EXT4_FC_SNAP_ERR_NONE = 0, > > + EXT4_FC_SNAP_ERR_ES_MISS = 1, > > + EXT4_FC_SNAP_ERR_ES_DELAYED = 2, > > + EXT4_FC_SNAP_ERR_ES_OTHER = 3, > > + EXT4_FC_SNAP_ERR_INODES_CAP = 4, > > + EXT4_FC_SNAP_ERR_RANGES_CAP = 5, > > + EXT4_FC_SNAP_ERR_NOMEM = 6, > > + EXT4_FC_SNAP_ERR_INODE_LOC = 7, > > You don't need to explicitly state the assignments, the enum will increment > them without them. Agree. > > +}; > > + > > /* > > * fourth extended file system inode data in memory > > */ > > diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c > > index d1eefee609120..4929e2990b292 100644 > > --- a/fs/ext4/fast_commit.c > > +++ b/fs/ext4/fast_commit.c > > @@ -193,6 +193,12 @@ static struct kmem_cache *ext4_fc_range_cachep; > > #define EXT4_FC_SNAPSHOT_MAX_INODES 1024 > > #define EXT4_FC_SNAPSHOT_MAX_RANGES 2048 > > > > +static inline void ext4_fc_set_snap_err(int *snap_err, int err) > > +{ > > + if (snap_err && *snap_err == EXT4_FC_SNAP_ERR_NONE) > > + *snap_err = err; > > +} > > + > > static void ext4_end_buffer_io_sync(struct buffer_head *bh, int uptodate) > > { > > BUFFER_TRACE(bh, ""); > > @@ -983,11 +989,12 @@ static void ext4_fc_free_inode_snap(struct inode > > *inode) > > static int ext4_fc_snapshot_inode_data(struct inode *inode, > > struct list_head *ranges, > > unsigned int nr_ranges_total, > > - unsigned int *nr_rangesp) > > + unsigned int *nr_rangesp, > > + int *snap_err) > > { > > struct ext4_inode_info *ei = EXT4_I(inode); > > - unsigned int nr_ranges = 0; > > ext4_lblk_t start_lblk, end_lblk, cur_lblk; > > + unsigned int nr_ranges = 0; > > > > spin_lock(&ei->i_fc_lock); > > if (ei->i_fc_lblk_len == 0) { > > @@ -1010,11 +1017,16 @@ static int ext4_fc_snapshot_inode_data(struct > > inode *inode, > > struct ext4_fc_range *range; > > ext4_lblk_t len; > > > > - if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL)) > > + if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL)) { > > + ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_MISS); > > return -EAGAIN; > > + } > > > > - if (ext4_es_is_delayed(&es)) > > + if (ext4_es_is_delayed(&es)) { > > + ext4_fc_set_snap_err(snap_err, > > + EXT4_FC_SNAP_ERR_ES_DELAYED); > > return -EAGAIN; > > + } > > > > len = es.es_len - (cur_lblk - es.es_lblk); > > if (len > end_lblk - cur_lblk + 1) > > @@ -1024,12 +1036,17 @@ static int ext4_fc_snapshot_inode_data(struct > > inode *inode, > > continue; > > } > > > > - if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES) > > + if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES) { > > + ext4_fc_set_snap_err(snap_err, > > + EXT4_FC_SNAP_ERR_RANGES_CAP); > > return -E2BIG; > > + } > > > > range = kmem_cache_alloc(ext4_fc_range_cachep, GFP_NOFS); > > - if (!range) > > + if (!range) { > > + ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM); > > return -ENOMEM; > > + } > > nr_ranges++; > > > > range->lblk = cur_lblk; > > @@ -1054,6 +1071,7 @@ static int ext4_fc_snapshot_inode_data(struct inode > > *inode, > > range->len = max; > > } else { > > kmem_cache_free(ext4_fc_range_cachep, range); > > + ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_OTHER); > > return -EAGAIN; > > } > > > > @@ -1070,7 +1088,7 @@ static int ext4_fc_snapshot_inode_data(struct inode > > *inode, > > > > static int ext4_fc_snapshot_inode(struct inode *inode, > > unsigned int nr_ranges_total, > > - unsigned int *nr_rangesp) > > + unsigned int *nr_rangesp, int *snap_err) > > { > > struct ext4_inode_info *ei = EXT4_I(inode); > > struct ext4_fc_inode_snap *snap; > > @@ -1082,8 +1100,10 @@ static int ext4_fc_snapshot_inode(struct inode > > *inode, > > int alloc_ctx; > > > > ret = ext4_get_inode_loc_noio(inode, &iloc); > > - if (ret) > > + if (ret) { > > + ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODE_LOC); > > return ret; > > + } > > > > if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA)) > > inode_len = EXT4_INODE_SIZE(inode->i_sb); > > @@ -1092,6 +1112,7 @@ static int ext4_fc_snapshot_inode(struct inode > > *inode, > > > > snap = kmalloc(struct_size(snap, inode_buf, inode_len), GFP_NOFS); > > if (!snap) { > > + ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM); > > brelse(iloc.bh); > > return -ENOMEM; > > } > > @@ -1102,7 +1123,7 @@ static int ext4_fc_snapshot_inode(struct inode > > *inode, > > brelse(iloc.bh); > > > > ret = ext4_fc_snapshot_inode_data(inode, &ranges, nr_ranges_total, > > - &nr_ranges); > > + &nr_ranges, snap_err); > > if (ret) { > > kfree(snap); > > ext4_fc_free_ranges(&ranges); > > @@ -1203,7 +1224,10 @@ static int ext4_fc_alloc_snapshot_inodes(struct > > super_block *sb, > > unsigned int *nr_inodesp); > > > > static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode > > **inodes, > > - unsigned int inodes_size) > > + unsigned int inodes_size, > > + unsigned int *nr_inodesp, > > + unsigned int *nr_rangesp, > > + int *snap_err) > > { > > struct super_block *sb = journal->j_private; > > struct ext4_sb_info *sbi = EXT4_SB(sb); > > @@ -1221,6 +1245,8 @@ static int ext4_fc_snapshot_inodes(journal_t > > *journal, struct inode **inodes, > > alloc_ctx = ext4_fc_lock(sb); > > list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) { > > if (i >= inodes_size) { > > + ext4_fc_set_snap_err(snap_err, > > + EXT4_FC_SNAP_ERR_INODES_CAP); > > ret = -E2BIG; > > goto unlock; > > } > > @@ -1244,6 +1270,8 @@ static int ext4_fc_snapshot_inodes(journal_t > > *journal, struct inode **inodes, > > continue; > > > > if (i >= inodes_size) { > > + ext4_fc_set_snap_err(snap_err, > > + EXT4_FC_SNAP_ERR_INODES_CAP); > > ret = -E2BIG; > > goto unlock; > > } > > @@ -1268,16 +1296,20 @@ static int ext4_fc_snapshot_inodes(journal_t > > *journal, struct inode **inodes, > > unsigned int inode_ranges = 0; > > > > ret = ext4_fc_snapshot_inode(inodes[idx], nr_ranges, > > - &inode_ranges); > > + &inode_ranges, snap_err); > > if (ret) > > break; > > nr_ranges += inode_ranges; > > } > > > > + if (nr_inodesp) > > + *nr_inodesp = i; > > + if (nr_rangesp) > > + *nr_rangesp = nr_ranges; > > return ret; > > } > > > > -static int ext4_fc_perform_commit(journal_t *journal) > > +static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid) > > { > > struct super_block *sb = journal->j_private; > > struct ext4_sb_info *sbi = EXT4_SB(sb); > > @@ -1286,10 +1318,15 @@ static int ext4_fc_perform_commit(journal_t > > *journal) > > struct inode *inode; > > struct inode **inodes; > > unsigned int inodes_size; > > + unsigned int snap_inodes = 0; > > + unsigned int snap_ranges = 0; > > + int snap_err = EXT4_FC_SNAP_ERR_NONE; > > struct blk_plug plug; > > int ret = 0; > > u32 crc = 0; > > int alloc_ctx; > > + ktime_t lock_start; > > + u64 locked_ns; > > > > /* > > * Step 1: Mark all inodes on s_fc_q[MAIN] with > > @@ -1337,13 +1374,13 @@ static int ext4_fc_perform_commit(journal_t > > *journal) > > if (ret) > > return ret; > > > > - > > ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size); > > if (ret) > > return ret; > > > > /* Step 4: Mark all inodes as being committed. */ > > jbd2_journal_lock_updates(journal); > > + lock_start = ktime_get(); > > /* > > * The journal is now locked. No more handles can start and all the > > * previous handles are now drained. Snapshotting happens in this > > @@ -1357,8 +1394,12 @@ static int ext4_fc_perform_commit(journal_t > > *journal) > > } > > ext4_fc_unlock(sb, alloc_ctx); > > > > - ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size); > > + ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size, > > + &snap_inodes, &snap_ranges, &snap_err); > > jbd2_journal_unlock_updates(journal); > > + locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start)); > > If locked_ns is only used for the tracepoint, it should either be > calculated in the tracepoint, or add: > > if (trace_ext4_fc_lock_updates_enabled()) { > locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start)); Good catch! > > + trace_ext4_fc_lock_updates(sb, commit_tid, locked_ns, snap_inodes, > > + snap_ranges, ret, snap_err); > > } > > Note, we are going to also add a code to call the tracepoint directly, to > remove the double static_branch. > > > https://lore.kernel.org/all/[email protected]/ > > But that code is still being worked on so you don't need to worry about it > at the moment. Thank you! I will monitor this patch set and incorporate it into future versions if possible. > > > kvfree(inodes); > > if (ret) > > return ret; > > @@ -1563,7 +1604,7 @@ int ext4_fc_commit(journal_t *journal, tid_t > > commit_tid) > > journal_ioprio = EXT4_DEF_JOURNAL_IOPRIO; > > set_task_ioprio(current, journal_ioprio); > > fc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize; > > - ret = ext4_fc_perform_commit(journal); > > + ret = ext4_fc_perform_commit(journal, commit_tid); > > if (ret < 0) { > > if (ret == -EAGAIN || ret == -E2BIG || ret == -ECANCELED) > > status = EXT4_FC_STATUS_INELIGIBLE; > > diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h > > index fd76d14c2776e..dc084f39b74ad 100644 > > --- a/include/trace/events/ext4.h > > +++ b/include/trace/events/ext4.h > > @@ -104,6 +104,26 @@ TRACE_DEFINE_ENUM(EXT4_FC_REASON_INODE_JOURNAL_DATA); > > TRACE_DEFINE_ENUM(EXT4_FC_REASON_ENCRYPTED_FILENAME); > > TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX); > > > > +#undef EM > > +#undef EMe > > +#define EM(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a); > > +#define EMe(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a); > > + > > +#define TRACE_SNAP_ERR \ > > + EM(NONE) \ > > + EM(ES_MISS) \ > > + EM(ES_DELAYED) \ > > + EM(ES_OTHER) \ > > + EM(INODES_CAP) \ > > + EM(RANGES_CAP) \ > > + EM(NOMEM) \ > > + EMe(INODE_LOC) > > + > > +TRACE_SNAP_ERR > > + > > +#undef EM > > +#undef EMe > > + > > #define show_fc_reason(reason) \ > > __print_symbolic(reason, \ > > { EXT4_FC_REASON_XATTR, "XATTR"}, \ > > @@ -2812,6 +2832,47 @@ TRACE_EVENT(ext4_fc_commit_stop, > > __entry->num_fc_ineligible, __entry->nblks_agg, __entry->tid) > > ); > > > > +#define EM(a) { EXT4_FC_SNAP_ERR_##a, #a }, > > +#define EMe(a) { EXT4_FC_SNAP_ERR_##a, #a } > > + > > +TRACE_EVENT(ext4_fc_lock_updates, > > + TP_PROTO(struct super_block *sb, tid_t commit_tid, u64 locked_ns, > > + unsigned int nr_inodes, unsigned int nr_ranges, int err, > > + int snap_err), > > + > > + TP_ARGS(sb, commit_tid, locked_ns, nr_inodes, nr_ranges, err, > > snap_err), > > + > > + TP_STRUCT__entry(/* entry */ > > + __field(dev_t, dev) > > + __field(tid_t, tid) > > + __field(u64, locked_ns) > > + __field(unsigned int, nr_inodes) > > + __field(unsigned int, nr_ranges) > > + __field(int, err) > > + __field(int, snap_err) > > + ), > > + > > + TP_fast_assign(/* assign */ > > + __entry->dev = sb->s_dev; > > + __entry->tid = commit_tid; > > + __entry->locked_ns = locked_ns; > > + __entry->nr_inodes = nr_inodes; > > + __entry->nr_ranges = nr_ranges; > > + __entry->err = err; > > + __entry->snap_err = snap_err; > > + ), > > + > > + TP_printk("dev %d,%d tid %u locked_ns %llu nr_inodes %u nr_ranges %u > > err %d snap_err %s", > > + MAJOR(__entry->dev), MINOR(__entry->dev), __entry->tid, > > + __entry->locked_ns, __entry->nr_inodes, __entry->nr_ranges, > > + __entry->err, __print_symbolic(__entry->snap_err, > > + TRACE_SNAP_ERR)) > > +); > > + > > +#undef EM > > +#undef EMe > > +#undef TRACE_SNAP_ERR > > + > > #define FC_REASON_NAME_STAT(reason) \ > > show_fc_reason(reason), \ > > __entry->fc_ineligible_rc[reason] > > Regards, Li
