[PATCH 3/4] gc docs: de-duplicate "OPTIONS" and "CONFIGURATION"

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

In an earlier commit I started including the "gc.*" documentation from
git-config(1) in the git-gc(1) documentation. That still left us in a
state where the "--auto" option and "gc.auto" were redundantly
discussing the same thing.

Fix that by briefly discussing how the option itself works for
"--auto", and for the rest referring to the configuration
documentation.

This revealed existing blind spots in the configuration documentation,
move over the documentation and reword as appropriate.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Documentation/config/gc.txt | 27 +++++++++++++++++++++++----
 Documentation/git-gc.txt    | 25 ++++---------------------
 2 files changed, 27 insertions(+), 25 deletions(-)

diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index a834a801cd6..605e14bc80b 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -19,13 +19,27 @@ gc.auto::
 	objects in the repository, `git gc --auto` will pack them.
 	Some Porcelain commands use this command to perform a
 	light-weight garbage collection from time to time.  The
-	default value is 6700.  Setting this to 0 disables it.
+	default value is 6700.
++
+Setting this to 0 disables not only automatic packing based on the
+number of loose objects, but any other heuristic `git gc --auto` will
+otherwise use to determine if there's work to do, such as
+`gc.autoPackLimit`.
++
+The repacking of loose objects will be performed with `git repack -d
+-l`.
 
 gc.autoPackLimit::
+
 	When there are more than this many packs that are not
 	marked with `*.keep` file in the repository, `git gc
 	--auto` consolidates them into one larger pack.  The
-	default	value is 50.  Setting this to 0 disables it.
+	default value is 50.  Setting this (or `gc.auto`) to 0
+	disables it. Packs will be consolidated using the `-A` option
+	of `git repack`.
++
+See the `gc.bigPackThreshold` configuration variable below. When in
+use it'll effect how the auto pack limit works.
 
 gc.autoDetach::
 	Make `git gc --auto` return immediately and run in background
@@ -35,13 +49,18 @@ gc.bigPackThreshold::
 	If non-zero, all packs larger than this limit are kept when
 	`git gc` is run. This is very similar to `--keep-base-pack`
 	except that all packs that meet the threshold are kept, not
-	just the base pack. Defaults to zero. Common unit suffixes of
-	'k', 'm', or 'g' are supported.
+	just the base pack. Defaults to zero or a memory heuristic.
+	Common unit suffixes of 'k', 'm', or 'g' are supported.
 +
 Note that if the number of kept packs is more than gc.autoPackLimit,
 this configuration variable is ignored, all packs except the base pack
 will be repacked. After this the number of packs should go below
 gc.autoPackLimit and gc.bigPackThreshold should be respected again.
++
+If the amount of memory is estimated not enough for `git repack` to
+run smoothly and `gc.bigPackThreshold` is not set, the largest pack
+will also be excluded (which is the equivalent of running `git gc`
+with `--keep-base-pack`).
 
 gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
index 9edf4e465b4..154c7c5e652 100644
--- a/Documentation/git-gc.txt
+++ b/Documentation/git-gc.txt
@@ -49,29 +49,12 @@ OPTIONS
 --auto::
 	With this option, 'git gc' checks whether any housekeeping is
 	required; if not, it exits without performing any work.
-	Some git commands run `git gc --auto` after performing
-	operations that could create many loose objects. Housekeeping
-	is required if there are too many loose objects or too many
-	packs in the repository.
 +
-If the number of loose objects exceeds the value of the `gc.auto`
-configuration variable, then all loose objects are combined into a
-single pack using `git repack -d -l`.  Setting the value of `gc.auto`
-to 0 disables automatic packing of loose objects.
+See the `gc.auto' option in the "CONFIGURATION" below for how this
+heuristic works.
 +
-If the number of packs exceeds the value of `gc.autoPackLimit`,
-then existing packs (except those marked with a `.keep` file
-or over `gc.bigPackThreshold` limit)
-are consolidated into a single pack by using the `-A` option of
-'git repack'.
-If the amount of memory is estimated not enough for `git repack` to
-run smoothly and `gc.bigPackThreshold` is not set, the largest
-pack will also be excluded (this is the equivalent of running `git gc`
-with `--keep-base-pack`).
-Setting `gc.autoPackLimit` to 0 disables automatic consolidation of
-packs.
-+
-If houskeeping is required due to many loose objects or packs, all
+Once housekeeping is triggered by exceeding the limits of
+configurations options such as `gc.auto` and `gc.autoPackLimit`, all
 other housekeeping tasks (e.g. rerere, working trees, reflog...) will
 be performed as well.
 
-- 
2.21.0.360.g471c308f928