Merge branch 'ds/maintenance-part-1'

A "git gc"'s big brother has been introduced to take care of more
repository maintenance tasks, not limited to the object database
cleaning.

* ds/maintenance-part-1:
  maintenance: add trace2 regions for task execution
  maintenance: add auto condition for commit-graph task
  maintenance: use pointers to check --auto
  maintenance: create maintenance.<task>.enabled config
  maintenance: take a lock on the objects directory
  maintenance: add --task option
  maintenance: add commit-graph task
  maintenance: initialize task array
  maintenance: replace run_auto_gc()
  maintenance: add --quiet option
  maintenance: create basic maintenance runner

5 files changed, 104 insertions, 5 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 3042d80978..f93b6837e4 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -398,6 +398,8 @@ include::config/mailinfo.txt[]
 
 include::config/mailmap.txt[]
 
+include::config/maintenance.txt[]
+
 include::config/man.txt[]
 
 include::config/merge.txt[]
diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
new file mode 100644
index 0000000000..7cc6700d57
--- /dev/null
+++ b/Documentation/config/maintenance.txt
@@ -0,0 +1,16 @@
+maintenance.<task>.enabled::
+	This boolean config option controls whether the maintenance task
+	with name `<task>` is run when no `--task` option is specified to
+	`git maintenance run`. These config values are ignored if a
+	`--task` option exists. By default, only `maintenance.gc.enabled`
+	is true.
+
+maintenance.commit-graph.auto::
+	This integer config option controls how often the `commit-graph` task
+	should be run as part of `git maintenance run --auto`. If zero, then
+	the `commit-graph` task will not run with the `--auto` option. A
+	negative value will force the task to run every time. Otherwise, a
+	positive value implies the command should run when the number of
+	reachable commits that are not in the commit-graph file is at least
+	the value of `maintenance.commit-graph.auto`. The default value is
+	100.
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index e8104c082e..2bf77b46fd 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -95,9 +95,11 @@ ifndef::git-pull[]
 	Allow several <repository> and <group> arguments to be
 	specified. No <refspec>s may be specified.
 
+--[no-]auto-maintenance::
 --[no-]auto-gc::
-	Run `git gc --auto` at the end to perform garbage collection
-	if needed. This is enabled by default.
+	Run `git maintenance run --auto` at the end to perform automatic
+	repository maintenance if needed. (`--[no-]auto-gc` is a synonym.)
+	This is enabled by default.
 
 --[no-]write-commit-graph::
 	Write a commit-graph after fetching. This overrides the config
diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index c898310099..097e6a86c5 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -78,9 +78,9 @@ repository using this option and then delete branches (or use any
 other Git command that makes any existing commit unreferenced) in the
 source repository, some objects may become unreferenced (or dangling).
 These objects may be removed by normal Git operations (such as `git commit`)
-which automatically call `git gc --auto`. (See linkgit:git-gc[1].)
-If these objects are removed and were referenced by the cloned repository,
-then the cloned repository will become corrupt.
+which automatically call `git maintenance run --auto`. (See
+linkgit:git-maintenance[1].) If these objects are removed and were referenced
+by the cloned repository, then the cloned repository will become corrupt.
 +
 Note that running `git repack` without the `--local` option in a repository
 cloned with `--shared` will copy objects from the source repository into a pack
diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
new file mode 100644
index 0000000000..6abcb8255a
--- /dev/null
+++ b/Documentation/git-maintenance.txt
@@ -0,0 +1,79 @@
+git-maintenance(1)
+==================
+
+NAME
+----
+git-maintenance - Run tasks to optimize Git repository data
+
+
+SYNOPSIS
+--------
+[verse]
+'git maintenance' run [<options>]
+
+
+DESCRIPTION
+-----------
+Run tasks to optimize Git repository data, speeding up other Git commands
+and reducing storage requirements for the repository.
+
+Git commands that add repository data, such as `git add` or `git fetch`,
+are optimized for a responsive user experience. These commands do not take
+time to optimize the Git data, since such optimizations scale with the full
+size of the repository while these user commands each perform a relatively
+small action.
+
+The `git maintenance` command provides flexibility for how to optimize the
+Git repository.
+
+SUBCOMMANDS
+-----------
+
+run::
+	Run one or more maintenance tasks. If one or more `--task` options
+	are specified, then those tasks are run in that order. Otherwise,
+	the tasks are determined by which `maintenance.<task>.enabled`
+	config options are true. By default, only `maintenance.gc.enabled`
+	is true.
+
+TASKS
+-----
+
+commit-graph::
+	The `commit-graph` job updates the `commit-graph` files incrementally,
+	then verifies that the written data is correct. The incremental
+	write is safe to run alongside concurrent Git processes since it
+	will not expire `.graph` files that were in the previous
+	`commit-graph-chain` file. They will be deleted by a later run based
+	on the expiration delay.
+
+gc::
+	Clean up unnecessary files and optimize the local repository. "GC"
+	stands for "garbage collection," but this task performs many
+	smaller tasks. This task can be expensive for large repositories,
+	as it repacks all Git objects into a single pack-file. It can also
+	be disruptive in some situations, as it deletes stale data. See
+	linkgit:git-gc[1] for more details on garbage collection in Git.
+
+OPTIONS
+-------
+--auto::
+	When combined with the `run` subcommand, run maintenance tasks
+	only if certain thresholds are met. For example, the `gc` task
+	runs when the number of loose objects exceeds the number stored
+	in the `gc.auto` config setting, or when the number of pack-files
+	exceeds the `gc.autoPackLimit` config setting.
+
+--quiet::
+	Do not report progress or other information over `stderr`.
+
+--task=<task>::
+	If this option is specified one or more times, then only run the
+	specified tasks in the specified order. If no `--task=<task>`
+	arguments are specified, then only the tasks with
+	`maintenance.<task>.enabled` configured as `true` are considered.
+	See the 'TASKS' section for the list of accepted `<task>` values.
+
+GIT
+---
+Part of the linkgit:git[1] suite