[PATCH 4/7] Default core.packdGitWindowSize to 1 MiB if NO_MMAP.

["Shawn O. Pearce" <spearce@spearce.org>]

If the compiler has asked us to disable use of mmap() on their
platform then we are forced to use git_mmap and its emulation via
pread.  In this case large (e.g. 32 MiB) windows for pack access
are simply too big as a command will wind up reading a lot more
data than it will ever need, significantly reducing response time.

To prevent a high latency when NO_MMAP has been selected we now
use a default of 1 MiB for core.packedGitWindowSize.  Credit goes
to Linus and Junio for recommending this more reasonable setting.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 environment.c     |    2 +-
 git-compat-util.h |    2 ++
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/environment.c b/environment.c
index 289fc84..e89aab4 100644
--- a/environment.c
+++ b/environment.c
@@ -22,7 +22,7 @@ char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace;
 int zlib_compression_level = Z_DEFAULT_COMPRESSION;
-size_t packed_git_window_size = 32 * 1024 * 1024;
+size_t packed_git_window_size = DEFAULT_packed_git_window_size;
 size_t packed_git_limit = 256 * 1024 * 1024;
 int pager_in_use;
 int pager_use_color = 1;
diff --git a/git-compat-util.h b/git-compat-util.h
index 5d9eb26..e056339 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -87,6 +87,7 @@ extern void set_warn_routine(void (*routine)(const char *warn, va_list params));
 #define MAP_FAILED ((void*)-1)
 #endif
 
+#define DEFAULT_packed_git_window_size (1 * 1024 * 1024)
 #define mmap git_mmap
 #define munmap git_munmap
 extern void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
@@ -95,6 +96,7 @@ extern int git_munmap(void *start, size_t length);
 #else /* NO_MMAP */
 
 #include <sys/mman.h>
+#define DEFAULT_packed_git_window_size (32 * 1024 * 1024)
 
 #endif /* NO_MMAP */
 
-- 
1.4.4.3.g2e63