社内勉強会のネタのフィードバックで…。¶
６月の社内勉強会の仮想化ネタに、QEMU & KQEMUの話をして、参加者が早速試してくれた。で、実メモリ4GBで、利用可能なメモリが2.7GBほどあったのに、メモリを2GB割り当てたら起動できなかったと聞き 1 、ハードコーディングされているんじゃないかと、QEMUのソースコード読んでみたら案の定だった。
vl.c
101 #define PHYS_RAM_MAX_SIZE (2047 * 1024 * 1024)
これじゃ、-m 2048とやったらダメだなぁ。でもなぜ2GB(2047MB)までにしているのかまでは分からず。どうしてなのだろう…。
以下は、qemu-0.9.0のコードよりメモリ割り当て関連のコードを抜粋。特定機能だけに注目して読めば読み易いなぁ。
vl.h
167 /* XXX: make it dynamic */
168 #if defined (TARGET_PPC) || defined (TARGET_SPARC64)
169 #define BIOS_SIZE ((512 + 32) * 1024)
170 #elif defined(TARGET_MIPS)
171 #define BIOS_SIZE (4 * 1024 * 1024)
172 #else
173 #define BIOS_SIZE ((256 + 64) * 1024)
174 #endif
~~~
863 /* vga.c */
864
865 #define VGA_RAM_SIZE (8192 * 1024)
vl.c
101 #define PHYS_RAM_MAX_SIZE (2047 * 1024 * 1024)
102
103 #ifdef TARGET_PPC
104 #define DEFAULT_RAM_SIZE 144
105 #else
106 #define DEFAULT_RAM_SIZE 128
107 #endif
~~~
6145
6146 enum {
~~~
6162 QEMU_OPTION_m,
~~~
6209 };
~~~
6217 const QEMUOption qemu_options[] = {
~~~
6234 { "m", HAS_ARG, QEMU_OPTION_m },
~~~
6295 { NULL },
6296 };
~~~
6499 int main(int argc, char **argv)
6500 {
~~~
6565 ram_size = DEFAULT_RAM_SIZE * 1024 * 1024;
6566 vga_ram_size = VGA_RAM_SIZE;
6567 bios_size = BIOS_SIZE;
~~~
6603 for(;;) {
6604 if (optind >= argc)
6605 break;
6606 r = argv[optind];
6607 if (r[0] != '-') {
6608 hd_filename[0] = argv[optind++];
6609 } else {
~~~
6638 switch(popt->index) {
~~~
6783 case QEMU_OPTION_m:
6784 ram_size = atoi(optarg) * 1024 * 1024;
6785 if (ram_size <= 0)
6786 help();
6787 if (ram_size > PHYS_RAM_MAX_SIZE) {
6788 fprintf(stderr, "qemu: at most %d MB RAM can be simulated\n",
6789 PHYS_RAM_MAX_SIZE / (1024 * 1024));
6790 exit(1);
6791 }
6792 break;
~~~
6961 }
6962 }
6963 }
~~~
7080 /* init the memory */
7081 phys_ram_size = ram_size + vga_ram_size + bios_size;
7082
7083 for (i = 0; i < nb_option_roms; i++) {
7084 int ret = get_image_size(option_rom[i]);
7085 if (ret == -1) {
7086 fprintf(stderr, "Could not load option rom '%s'\n", option_rom[i]);
7087 exit(1);
7088 }
7089 phys_ram_size += ret;
7090 }
7091
7092 phys_ram_base = qemu_vmalloc(phys_ram_size);
7093 if (!phys_ram_base) {
7094 fprintf(stderr, "Could not allocate physical memory\n");
7095 exit(1);
7096 }
~~~
7269 }
osdep.c
63 #if defined(_WIN32)
64
65 void *qemu_vmalloc(size_t size)
66 {
67 /* FIXME: this is not exactly optimal solution since VirtualAlloc
68 has 64Kb granularity, but at least it guarantees us that the
69 memory is page aligned. */
70 return VirtualAlloc(NULL, size, MEM_COMMIT, PAGE_READWRITE);
71 }
~~~
86 void *kqemu_vmalloc(size_t size)
87 {
88 static int phys_ram_fd = -1;
89 static int phys_ram_size = 0;
90 const char *tmpdir;
91 char phys_ram_file[1024];
92 void *ptr;
93 #ifdef HOST_SOLARIS
94 struct statvfs stfs;
95 #else
96 struct statfs stfs;
97 #endif
98
99 if (phys_ram_fd < 0) {
100 tmpdir = getenv("QEMU_TMPDIR");
101 if (!tmpdir)
102 #ifdef HOST_SOLARIS
103 tmpdir = "/tmp";
104 if (statvfs(tmpdir, &stfs) == 0) {
105 #else
106 tmpdir = "/dev/shm";
107 if (statfs(tmpdir, &stfs) == 0) {
108 #endif
109 int64_t free_space;
110 int ram_mb;
111
112 extern int ram_size;
113 free_space = (int64_t)stfs.f_bavail * stfs.f_bsize;
114 if ((ram_size + 8192 * 1024) >= free_space) {
115 ram_mb = (ram_size / (1024 * 1024));
116 fprintf(stderr,
117 "You do not have enough space in '%s' for the %d MB of QEMU virtual RAM.\n",
118 tmpdir, ram_mb);
119 if (strcmp(tmpdir, "/dev/shm") == 0) {
120 fprintf(stderr, "To have more space available provided you have enough RAM and swap, do as root:\n"
121 "umount /dev/shm\n"
122 "mount -t tmpfs -o size=%dm none /dev/shm\n",
123 ram_mb + 16);
124 } else {
125 fprintf(stderr,
126 "Use the '-m' option of QEMU to diminish the amount of virtual RAM or use the\n"
127 "QEMU_TMPDIR environment variable to set another directory where the QEMU\n"
128 "temporary RAM file will be opened.\n");
129 }
130 fprintf(stderr, "Or disable the accelerator module with -no-kqemu\n");
131 exit(1);
132 }
133 }
134 snprintf(phys_ram_file, sizeof(phys_ram_file), "%s/qemuXXXXXX",
135 tmpdir);
136 phys_ram_fd = mkstemp(phys_ram_file);
137 if (phys_ram_fd < 0) {
138 fprintf(stderr,
139 "warning: could not create temporary file in '%s'.\n"
140 "Use QEMU_TMPDIR to select a directory in a tmpfs filesystem.\n"
141 "Using '/tmp' as fallback.\n",
142 tmpdir);
143 snprintf(phys_ram_file, sizeof(phys_ram_file), "%s/qemuXXXXXX",
144 "/tmp");
145 phys_ram_fd = mkstemp(phys_ram_file);
146 if (phys_ram_fd < 0) {
147 fprintf(stderr, "Could not create temporary memory file '%s'\n",
148 phys_ram_file);
149 exit(1);
150 }
151 }
152 unlink(phys_ram_file);
153 }
154 size = (size + 4095) & ~4095;
155 ftruncate(phys_ram_fd, phys_ram_size + size);
156 ptr = mmap(NULL,
157 size,
158 PROT_WRITE | PROT_READ, MAP_SHARED,
159 phys_ram_fd, phys_ram_size);
160 if (ptr == MAP_FAILED) {
161 fprintf(stderr, "Could not map physical memory\n");
162 exit(1);
163 }
164 phys_ram_size += size;
165 return ptr;
166 }
~~~
175 /* alloc shared memory pages */
176 void *qemu_vmalloc(size_t size)
177 {
178 #if defined(USE_KQEMU)
179 if (kqemu_allowed)
180 return kqemu_vmalloc(size);
181 #endif
182 #ifdef _BSD
183 return valloc(size);
184 #else
185 return memalign(4096, size);
186 #endif
187 }
- 1
4GBもメモリ積んでるPC無いからそんなん知らんかった。