Merge branch 'sp/mmap'

* sp/mmap: (27 commits)
  Spell default packedgitlimit slightly differently
  Increase packedGit{Limit,WindowSize} on 64 bit systems.
  Update packedGit config option documentation.
  mmap: set FD_CLOEXEC for file descriptors we keep open for mmap()
  pack-objects: fix use of use_pack().
  Fix random segfaults in pack-objects.
  Cleanup read_cache_from error handling.
  Replace mmap with xmmap, better handling MAP_FAILED.
  Release pack windows before reporting out of memory.
  Default core.packdGitWindowSize to 1 MiB if NO_MMAP.
  Test suite for sliding window mmap implementation.
  Create pack_report() as a debugging aid.
  Support unmapping windows on 'temporary' packfiles.
  Improve error message when packfile mmap fails.
  Ensure core.packedGitWindowSize cannot be less than 2 pages.
  Load core configuration in git-verify-pack.
  Fully activate the sliding window pack access.
  Unmap individual windows rather than entire files.
  Document why header parsing won't exceed a window.
  Loop over pack_windows when inflating/accessing data.
  ...

Conflicts:

	cache.h
	pack-check.c

Documentation/config.txt

@@ -118,6 +118,34 @@ core.legacyheaders::
 	database directly (where the "http://" and "rsync://" protocols
 	count as direct access).
 
+core.packedGitWindowSize::
+	Number of bytes of a pack file to map into memory in a
+	single mapping operation.  Larger window sizes may allow
+	your system to process a smaller number of large pack files
+	more quickly.  Smaller window sizes will negatively affect
+	performance due to increased calls to the operating system's
+	memory manager, but may improve performance when accessing
+	a large number of large pack files.
++
+Default is 1 MiB if NO_MMAP was set at compile time, otherwise 32
+MiB on 32 bit platforms and 1 GiB on 64 bit platforms.  This should
+be reasonable for all users/operating systems.  You probably do
+not need to adjust this value.
++
+Common unit suffixes of 'k', 'm', or 'g' are supported.
+
+core.packedGitLimit::
+	Maximum number of bytes to map simultaneously into memory
+	from pack files.  If Git needs to access more than this many
+	bytes at once to complete an operation it will unmap existing
+	regions to reclaim virtual address space within the process.
++
+Default is 256 MiB on 32 bit platforms and 8 GiB on 64 bit platforms.
+This should be reasonable for all users/operating systems, except on
+the largest projects.  You probably do not need to adjust this value.
++
+Common unit suffixes of 'k', 'm', or 'g' are supported.
+
 alias.*::
 	Command aliases for the gitlink:git[1] command wrapper - e.g.
 	after defining "alias.last = cat-file commit HEAD", the invocation