index-pack usage of mmap() is unacceptably slower on many OSes other than Linux

It was reported by Randal L. Schwartz <merlyn@stonehenge.com> that
indexing the Linux repository ~150MB pack takes about an hour on OS x
while it's a minute on Linux.  It seems that the OS X mmap()
implementation is more than 2 orders of magnitude slower than the Linux
one.

Linus proposed a patch replacing mmap() with pread() bringing index-pack
performance on OS X in line with the Linux one.  The performances on
Linux also improved by a small margin.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/index-pack.c b/index-pack.c
index 6d6c92bf14803923f4c98678ae682aef4d41d3ab..c05feae16172ab4bae73cb5b2501dfde418ad5d8 100644 (file)
--- a/index-pack.c
+++ b/index-pack.c
@@ -1,3 +1,8 @@
+#define _XOPEN_SOURCE 600
+#include <unistd.h>
+#include <sys/time.h>
+#include <signal.h>
+
 #include "cache.h"
 #include "delta.h"
 #include "pack.h"
@@ -6,8 +11,6 @@
 #include "commit.h"
 #include "tag.h"
 #include "tree.h"
-#include <sys/time.h>
-#include <signal.h>
 
 static const char index_pack_usage[] =
 "git-index-pack [-v] [-o <index-file>] [{ ---keep | --keep=<msg> }] { <pack-file> | --stdin [--fix-thin] [<pack-file>] }";
@@ -87,7 +90,7 @@ static unsigned display_progress(unsigned n, unsigned total, unsigned last_pc)
 static unsigned char input_buffer[4096];
 static unsigned long input_offset, input_len, consumed_bytes;
 static SHA_CTX input_ctx;
-static int input_fd, output_fd, mmap_fd;
+static int input_fd, output_fd, pack_fd;
 
 /* Discard current buffer used content. */
 static void flush(void)
@@ -148,14 +151,14 @@ static const char *open_pack_file(const char *pack_name)
                        output_fd = open(pack_name, O_CREAT|O_EXCL|O_RDWR, 0600);
                if (output_fd < 0)
                        die("unable to create %s: %s\n", pack_name, strerror(errno));
-               mmap_fd = output_fd;
+               pack_fd = output_fd;
        } else {
                input_fd = open(pack_name, O_RDONLY);
                if (input_fd < 0)
                        die("cannot open packfile '%s': %s",
                            pack_name, strerror(errno));
                output_fd = -1;
-               mmap_fd = input_fd;
+               pack_fd = input_fd;
        }
        SHA1_Init(&input_ctx);
        return pack_name;
@@ -279,27 +282,25 @@ static void *get_data_from_pack(struct object_entry *obj)
 {
        unsigned long from = obj[0].offset + obj[0].hdr_size;
        unsigned long len = obj[1].offset - from;
-       unsigned pg_offset = from % getpagesize();
-       unsigned char *map, *data;
+       unsigned char *src, *data;
        z_stream stream;
        int st;
 
-       map = mmap(NULL, len + pg_offset, PROT_READ, MAP_PRIVATE,
-                  mmap_fd, from - pg_offset);
-       if (map == MAP_FAILED)
-               die("cannot mmap pack file: %s", strerror(errno));
+       src = xmalloc(len);
+       if (pread(pack_fd, src, len, from) != len)
+               die("cannot pread pack file: %s", strerror(errno));
        data = xmalloc(obj->size);
        memset(&stream, 0, sizeof(stream));
        stream.next_out = data;
        stream.avail_out = obj->size;
-       stream.next_in = map + pg_offset;
+       stream.next_in = src;
        stream.avail_in = len;
        inflateInit(&stream);
        while ((st = inflate(&stream, Z_FINISH)) == Z_OK);
        inflateEnd(&stream);
        if (st != Z_STREAM_END || stream.total_out != obj->size)
                die("serious inflate inconsistency");
-       munmap(map, len + pg_offset);
+       free(src);
        return data;
 }