+static uint64_t total_ram(void)
+{
+#if defined(HAVE_SYSINFO)
+ struct sysinfo si;
+
+ if (!sysinfo(&si))
+ return si.totalram;
+#elif defined(HAVE_BSD_SYSCTL) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM))
+ int64_t physical_memory;
+ int mib[2];
+ size_t length;
+
+ mib[0] = CTL_HW;
+# if defined(HW_MEMSIZE)
+ mib[1] = HW_MEMSIZE;
+# else
+ mib[1] = HW_PHYSMEM;
+# endif
+ length = sizeof(int64_t);
+ if (!sysctl(mib, 2, &physical_memory, &length, NULL, 0))
+ return physical_memory;
+#elif defined(GIT_WINDOWS_NATIVE)
+ MEMORYSTATUSEX memInfo;
+
+ memInfo.dwLength = sizeof(MEMORYSTATUSEX);
+ if (GlobalMemoryStatusEx(&memInfo))
+ return memInfo.ullTotalPhys;
+#endif
+ return 0;
+}
+
+static uint64_t estimate_repack_memory(struct packed_git *pack)
+{
+ unsigned long nr_objects = approximate_object_count();
+ size_t os_cache, heap;
+
+ if (!pack || !nr_objects)
+ return 0;
+
+ /*
+ * First we have to scan through at least one pack.
+ * Assume enough room in OS file cache to keep the entire pack
+ * or we may accidentally evict data of other processes from
+ * the cache.
+ */
+ os_cache = pack->pack_size + pack->index_size;
+ /* then pack-objects needs lots more for book keeping */
+ heap = sizeof(struct object_entry) * nr_objects;
+ /*
+ * internal rev-list --all --objects takes up some memory too,
+ * let's say half of it is for blobs
+ */
+ heap += sizeof(struct blob) * nr_objects / 2;
+ /*
+ * and the other half is for trees (commits and tags are
+ * usually insignificant)
+ */
+ heap += sizeof(struct tree) * nr_objects / 2;
+ /* and then obj_hash[], underestimated in fact */
+ heap += sizeof(struct object *) * nr_objects;
+ /* revindex is used also */
+ heap += sizeof(struct revindex_entry) * nr_objects;
+ /*
+ * read_sha1_file() (either at delta calculation phase, or
+ * writing phase) also fills up the delta base cache
+ */
+ heap += delta_base_cache_limit;
+ /* and of course pack-objects has its own delta cache */
+ heap += max_delta_cache_size;
+
+ return os_cache + heap;
+}
+