[{"id":3674974,"web_url":"http://patchwork.ozlabs.org/comment/3674974/","msgid":"<20260408160405.45a5ee09@gandalf.local.home>","list_archive_url":null,"date":"2026-04-08T20:04:05","subject":"Re: [RFC v6 6/7] ext4: fast commit: add lock_updates tracepoint","submitter":{"id":112,"url":"http://patchwork.ozlabs.org/api/people/112/","name":"Steven Rostedt","email":"rostedt@goodmis.org"},"content":"On Wed, 8 Apr 2026 19:20:17 +0800\nLi Chen wrote:\n\n> Commit-time fast commit snapshots run under jbd2_journal_lock_updates(),\n> so it is useful to quantify the time spent with updates locked and to\n> understand why snapshotting can fail.\n> \n> Add a new tracepoint, ext4_fc_lock_updates, reporting the time spent in\n> the updates-locked window along with the number of snapshotted inodes\n> and ranges. Record the first snapshot failure reason in a stable snap_err\n> field for tooling.\n> \n\n[..]\n\n> @@ -1338,13 +1375,13 @@ static int ext4_fc_perform_commit(journal_t *journal)\n> \tif (ret)\n> \t\treturn ret;\n> \n> -\n> \tret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size);\n> \tif (ret)\n> \t\treturn ret;\n> \n> \t/* Step 4: Mark all inodes as being committed. */\n> \tjbd2_journal_lock_updates(journal);\n> +\tlock_start = ktime_get();\n\nktime_get() is rather quick but if you care about micro-optimizations, you\ncould have:\n\n\tif (trace_ext4_fc_lock_updates_enabled())\n\t\tlock_start = ktime_get();\n\telse\t\n\t\tlock_start = 0;\n\n> \t/*\n> \t * The journal is now locked. No more handles can start and all the\n> \t * previous handles are now drained. Snapshotting happens in this\n> @@ -1358,8 +1395,15 @@ static int ext4_fc_perform_commit(journal_t *journal)\n> \t}\n> \text4_fc_unlock(sb, alloc_ctx);\n> \n> -\tret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size);\n> +\tret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size,\n> +\t\t\t\t &snap_inodes, &snap_ranges, &snap_err);\n> \tjbd2_journal_unlock_updates(journal);\n> +\tif (trace_ext4_fc_lock_updates_enabled()) {\n\n\tif (trace_ext4_fc_lock_updates_enabled() && lock_start) {\n\nBut feel free to ignore this if the overhead of always calling ktime_get()\nis not an issue.\n\n\n> +\t\tlocked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start));\n> +\t\ttrace_ext4_fc_lock_updates(sb, commit_tid, locked_ns,\n> +\t\t\t\t\t snap_inodes, snap_ranges, ret,\n> +\t\t\t\t\t snap_err);\n> +\t}\n> \tkvfree(inodes);\n> \tif (ret)\n> \t\treturn ret;\n> @@ -1564,7 +1608,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)\n> \t\tjournal_ioprio = EXT4_DEF_JOURNAL_IOPRIO;\n> \tset_task_ioprio(current, journal_ioprio);\n> \tfc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize;\n> -\tret = ext4_fc_perform_commit(journal);\n> +\tret = ext4_fc_perform_commit(journal, commit_tid);\n> \tif (ret < 0) {\n> \t\tif (ret == -EAGAIN || ret == -E2BIG || ret == -ECANCELED)\n> \t\t\tstatus = EXT4_FC_STATUS_INELIGIBLE;\n> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h\n> index f493642cf121..7028a28316fa 100644\n> --- a/include/trace/events/ext4.h\n> +++ b/include/trace/events/ext4.h\n> @@ -107,6 +107,26 @@ TRACE_DEFINE_ENUM(EXT4_FC_REASON_VERITY);\n> TRACE_DEFINE_ENUM(EXT4_FC_REASON_MOVE_EXT);\n> TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);\n> \n> +#undef EM\n> +#undef EMe\n> +#define EM(a)\tTRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);\n> +#define EMe(a)\tTRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);\n> +\n> +#define TRACE_SNAP_ERR\t\t\t\t\t\t\\\n> +\tEM(NONE)\t\t\t\t\t\t\\\n> +\tEM(ES_MISS)\t\t\t\t\t\t\\\n> +\tEM(ES_DELAYED)\t\t\t\t\t\t\\\n> +\tEM(ES_OTHER)\t\t\t\t\t\t\\\n> +\tEM(INODES_CAP)\t\t\t\t\t\t\\\n> +\tEM(RANGES_CAP)\t\t\t\t\t\t\\\n> +\tEM(NOMEM)\t\t\t\t\t\t\\\n> +\tEMe(INODE_LOC)\n> +\n> +TRACE_SNAP_ERR\n> +\n> +#undef EM\n> +#undef EMe\n> +\n> #define show_fc_reason(reason)\t\t\t\t\t\t\\\n> \t__print_symbolic(reason,\t\t\t\t\t\\\n> \t\t{ EXT4_FC_REASON_XATTR,\t\t\"XATTR\"},\t\t\\\n> @@ -2818,6 +2838,47 @@ TRACE_EVENT(ext4_fc_commit_stop,\n> \t\t __entry->num_fc_ineligible, __entry->nblks_agg, __entry->tid)\n> );\n> \n> +#define EM(a)\t{ EXT4_FC_SNAP_ERR_##a, #a },\n> +#define EMe(a)\t{ EXT4_FC_SNAP_ERR_##a, #a }\n> +\n> +TRACE_EVENT(ext4_fc_lock_updates,\n> +\t TP_PROTO(struct super_block *sb, tid_t commit_tid, u64 locked_ns,\n> +\t\t unsigned int nr_inodes, unsigned int nr_ranges, int err,\n> +\t\t int snap_err),\n> +\n> +\tTP_ARGS(sb, commit_tid, locked_ns, nr_inodes, nr_ranges, err, snap_err),\n> +\n> +\tTP_STRUCT__entry(/* entry */\n> +\t\t__field(dev_t, dev)\n> +\t\t__field(tid_t, tid)\n> +\t\t__field(u64, locked_ns)\n> +\t\t__field(unsigned int, nr_inodes)\n> +\t\t__field(unsigned int, nr_ranges)\n> +\t\t__field(int, err)\n> +\t\t__field(int, snap_err)\n> +\t),\n> +\n> +\tTP_fast_assign(/* assign */\n> +\t\t__entry->dev = sb->s_dev;\n> +\t\t__entry->tid = commit_tid;\n> +\t\t__entry->locked_ns = locked_ns;\n> +\t\t__entry->nr_inodes = nr_inodes;\n> +\t\t__entry->nr_ranges = nr_ranges;\n> +\t\t__entry->err = err;\n> +\t\t__entry->snap_err = snap_err;\n> +\t),\n> +\n> +\tTP_printk(\"dev %d,%d tid %u locked_ns %llu nr_inodes %u nr_ranges %u err %d snap_err %s\",\n> +\t\t MAJOR(__entry->dev), MINOR(__entry->dev), __entry->tid,\n> +\t\t __entry->locked_ns, __entry->nr_inodes, __entry->nr_ranges,\n> +\t\t __entry->err, __print_symbolic(__entry->snap_err,\n> +\t\t\t\t\t\t TRACE_SNAP_ERR))\n> +);\n> +\n> +#undef EM\n> +#undef EMe\n> +#undef TRACE_SNAP_ERR\n> +\n> #define FC_REASON_NAME_STAT(reason)\t\t\t\t\t\\\n> \tshow_fc_reason(reason),\t\t\t\t\t\t\\\n> \t__entry->fc_ineligible_rc[reason]\n\nAs for the rest:\n\nReviewed-by: Steven Rostedt (Google) \n\n[ Please add this reviewed-by to any new versions so I remember I already\n looked at it. ]\n\nThanks,\n\n-- Steve","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-ext4@vger.kernel.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","patchwork-incoming@ozlabs.org"],"Authentication-Results":["legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=ozlabs.org\n (client-ip=150.107.74.76; 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Record the first snapshot failure reason in a stable snap_err\n > > field for tooling.\n > > \n > \n > [..]\n > \n > > @@ -1338,13 +1375,13 @@ static int ext4_fc_perform_commit(journal_t *journal)\n > > if (ret)\n > > return ret;\n > > \n > > -\n > > ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size);\n > > if (ret)\n > > return ret;\n > > \n > > /* Step 4: Mark all inodes as being committed. */\n > > jbd2_journal_lock_updates(journal);\n > > + lock_start = ktime_get();\n > \n > ktime_get() is rather quick but if you care about micro-optimizations, you\n > could have:\n > \n > if (trace_ext4_fc_lock_updates_enabled())\n > lock_start = ktime_get();\n > else \n > lock_start = 0;\n > \n > > /*\n > > * The journal is now locked. No more handles can start and all the\n > > * previous handles are now drained. Snapshotting happens in this\n > > @@ -1358,8 +1395,15 @@ static int ext4_fc_perform_commit(journal_t *journal)\n > > }\n > > ext4_fc_unlock(sb, alloc_ctx);\n > > \n > > - ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size);\n > > + ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size,\n > > + &snap_inodes, &snap_ranges, &snap_err);\n > > jbd2_journal_unlock_updates(journal);\n > > + if (trace_ext4_fc_lock_updates_enabled()) {\n > \n > if (trace_ext4_fc_lock_updates_enabled() && lock_start) {\n > \n > But feel free to ignore this if the overhead of always calling ktime_get()\n > is not an issue.\n > \n > \n > > + locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start));\n > > + trace_ext4_fc_lock_updates(sb, commit_tid, locked_ns,\n > > + snap_inodes, snap_ranges, ret,\n > > + snap_err);\n > > + }\n > > kvfree(inodes);\n > > if (ret)\n > > return ret;\n > > @@ -1564,7 +1608,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)\n > > journal_ioprio = EXT4_DEF_JOURNAL_IOPRIO;\n > > set_task_ioprio(current, journal_ioprio);\n > > fc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize;\n > > - ret = ext4_fc_perform_commit(journal);\n > > + ret = ext4_fc_perform_commit(journal, commit_tid);\n > > if (ret < 0) {\n > > if (ret == -EAGAIN || ret == -E2BIG || ret == -ECANCELED)\n > > status = EXT4_FC_STATUS_INELIGIBLE;\n > > diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h\n > > index f493642cf121..7028a28316fa 100644\n > > --- a/include/trace/events/ext4.h\n > > +++ b/include/trace/events/ext4.h\n > > @@ -107,6 +107,26 @@ TRACE_DEFINE_ENUM(EXT4_FC_REASON_VERITY);\n > > TRACE_DEFINE_ENUM(EXT4_FC_REASON_MOVE_EXT);\n > > TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);\n > > \n > > +#undef EM\n > > +#undef EMe\n > > +#define EM(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);\n > > +#define EMe(a) TRACE_DEFINE_ENUM(EXT4_FC_SNAP_ERR_##a);\n > > +\n > > +#define TRACE_SNAP_ERR \\\n > > + EM(NONE) \\\n > > + EM(ES_MISS) \\\n > > + EM(ES_DELAYED) \\\n > > + EM(ES_OTHER) \\\n > > + EM(INODES_CAP) \\\n > > + EM(RANGES_CAP) \\\n > > + EM(NOMEM) \\\n > > + EMe(INODE_LOC)\n > > +\n > > +TRACE_SNAP_ERR\n > > +\n > > +#undef EM\n > > +#undef EMe\n > > +\n > > #define show_fc_reason(reason) \\\n > > __print_symbolic(reason, \\\n > > { EXT4_FC_REASON_XATTR, \"XATTR\"}, \\\n > > @@ -2818,6 +2838,47 @@ TRACE_EVENT(ext4_fc_commit_stop,\n > > __entry->num_fc_ineligible, __entry->nblks_agg, __entry->tid)\n > > );\n > > \n > > +#define EM(a) { EXT4_FC_SNAP_ERR_##a, #a },\n > > +#define EMe(a) { EXT4_FC_SNAP_ERR_##a, #a }\n > > +\n > > +TRACE_EVENT(ext4_fc_lock_updates,\n > > + TP_PROTO(struct super_block *sb, tid_t commit_tid, u64 locked_ns,\n > > + unsigned int nr_inodes, unsigned int nr_ranges, int err,\n > > + int snap_err),\n > > +\n > > + TP_ARGS(sb, commit_tid, locked_ns, nr_inodes, nr_ranges, err, snap_err),\n > > +\n > > + TP_STRUCT__entry(/* entry */\n > > + __field(dev_t, dev)\n > > + __field(tid_t, tid)\n > > + __field(u64, locked_ns)\n > > + __field(unsigned int, nr_inodes)\n > > + __field(unsigned int, nr_ranges)\n > > + __field(int, err)\n > > + __field(int, snap_err)\n > > + ),\n > > +\n > > + TP_fast_assign(/* assign */\n > > + __entry->dev = sb->s_dev;\n > > + __entry->tid = commit_tid;\n > > + __entry->locked_ns = locked_ns;\n > > + __entry->nr_inodes = nr_inodes;\n > > + __entry->nr_ranges = nr_ranges;\n > > + __entry->err = err;\n > > + __entry->snap_err = snap_err;\n > > + ),\n > > +\n > > + TP_printk(\"dev %d,%d tid %u locked_ns %llu nr_inodes %u nr_ranges %u err %d snap_err %s\",\n > > + MAJOR(__entry->dev), MINOR(__entry->dev), __entry->tid,\n > > + __entry->locked_ns, __entry->nr_inodes, __entry->nr_ranges,\n > > + __entry->err, __print_symbolic(__entry->snap_err,\n > > + TRACE_SNAP_ERR))\n > > +);\n > > +\n > > +#undef EM\n > > +#undef EMe\n > > +#undef TRACE_SNAP_ERR\n > > +\n > > #define FC_REASON_NAME_STAT(reason) \\\n > > show_fc_reason(reason), \\\n > > __entry->fc_ineligible_rc[reason]\n > \n > As for the rest:\n > \n > Reviewed-by: Steven Rostedt (Google) \n > \n > [ Please add this reviewed-by to any new versions so I remember I already\n > looked at it. ]\n\nSure, thanks a lot for your thoughtful review!\n\nRegards,\nLi​","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-ext4@vger.kernel.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","patchwork-incoming@ozlabs.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=linux.beauty header.i=me@linux.beauty\n header.a=rsa-sha256 header.s=zmail header.b=KuvYusmn;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=ozlabs.org\n (client-ip=2404:9400:2221:ea00::3; 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