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Re: [Qemu-devel] [PATCH] Save memory allocation in the elf loader
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] Save memory allocation in the elf loader |
Date: |
Tue, 19 Feb 2013 16:51:50 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
Il 19/02/2013 15:41, Fabien Chouteau ha scritto:
> The current elf loader uses too much memory. For example, I have a
> executable with a bss section of 400 MB and I set the ram size to 512
> MB. Qemu uses about 780MB of RAM (which is fine), but there's a peak at
> 1.6 GB during initialization (this is not fine).
>
> This patch fixes two things:
> 1) do not allocate each elf program twice.
> 2) do not allocate memory for areas that are only zeros.
>
> For this we need a new field in Rom: "datasize" which is the size of the
> allocated data. If datasize is less than romsize, it means that the area
> from datasize to romsize is filled with zeros.
You haven't CCed the only two people that likely would review your patch. :)
Paolo
> Signed-off-by: Fabien Chouteau <address@hidden>
> ---
> hw/elf_ops.h | 19 ++++++++-------
> hw/loader.c | 75
> ++++++++++++++++++++++++++++++++++++++++++++++++----------
> hw/loader.h | 2 ++
> 3 files changed, 75 insertions(+), 21 deletions(-)
>
> diff --git a/hw/elf_ops.h b/hw/elf_ops.h
> index 531a425..acc701e 100644
> --- a/hw/elf_ops.h
> +++ b/hw/elf_ops.h
> @@ -197,7 +197,7 @@ static int glue(load_elf, SZ)(const char *name, int fd,
> struct elfhdr ehdr;
> struct elf_phdr *phdr = NULL, *ph;
> int size, i, total_size;
> - elf_word mem_size;
> + elf_word mem_size, file_size;
> uint64_t addr, low = (uint64_t)-1, high = 0;
> uint8_t *data = NULL;
> char label[128];
> @@ -252,14 +252,16 @@ static int glue(load_elf, SZ)(const char *name, int fd,
> for(i = 0; i < ehdr.e_phnum; i++) {
> ph = &phdr[i];
> if (ph->p_type == PT_LOAD) {
> - mem_size = ph->p_memsz;
> - /* XXX: avoid allocating */
> - data = g_malloc0(mem_size);
> + mem_size = ph->p_memsz; /* Size of the ROM */
> + file_size = ph->p_filesz; /* Size of the allocated data */
> + data = g_malloc0(file_size);
> if (ph->p_filesz > 0) {
> - if (lseek(fd, ph->p_offset, SEEK_SET) < 0)
> + if (lseek(fd, ph->p_offset, SEEK_SET) < 0) {
> goto fail;
> - if (read(fd, data, ph->p_filesz) != ph->p_filesz)
> + }
> + if (read(fd, data, file_size) != file_size) {
> goto fail;
> + }
> }
> /* address_offset is hack for kernel images that are
> linked at the wrong physical address. */
> @@ -281,7 +283,9 @@ static int glue(load_elf, SZ)(const char *name, int fd,
> }
>
> snprintf(label, sizeof(label), "phdr #%d: %s", i, name);
> - rom_add_blob_fixed(label, data, mem_size, addr);
> +
> + /* rom_add_elf_program() seize the ownership of 'data' */
> + rom_add_elf_program(label, data, file_size, mem_size, addr);
>
> total_size += mem_size;
> if (addr < low)
> @@ -289,7 +293,6 @@ static int glue(load_elf, SZ)(const char *name, int fd,
> if ((addr + mem_size) > high)
> high = addr + mem_size;
>
> - g_free(data);
> data = NULL;
> }
> }
> diff --git a/hw/loader.c b/hw/loader.c
> index 995edc3..bd2b52d 100644
> --- a/hw/loader.c
> +++ b/hw/loader.c
> @@ -533,7 +533,14 @@ typedef struct Rom Rom;
> struct Rom {
> char *name;
> char *path;
> +
> + /* datasize is the amount of memory allocated in "data". If datasize is
> less
> + * than romsize, it means that the area from datasize to romsize is
> filled
> + * with zeros.
> + */
> size_t romsize;
> + size_t datasize;
> +
> uint8_t *data;
> int isrom;
> char *fw_dir;
> @@ -589,14 +596,15 @@ int rom_add_file(const char *file, const char *fw_dir,
> rom->fw_dir = g_strdup(fw_dir);
> rom->fw_file = g_strdup(file);
> }
> - rom->addr = addr;
> - rom->romsize = lseek(fd, 0, SEEK_END);
> - rom->data = g_malloc0(rom->romsize);
> + rom->addr = addr;
> + rom->romsize = lseek(fd, 0, SEEK_END);
> + rom->datasize = rom->romsize;
> + rom->data = g_malloc0(rom->datasize);
> lseek(fd, 0, SEEK_SET);
> - rc = read(fd, rom->data, rom->romsize);
> - if (rc != rom->romsize) {
> + rc = read(fd, rom->data, rom->datasize);
> + if (rc != rom->datasize) {
> fprintf(stderr, "rom: file %-20s: read error: rc=%d (expected
> %zd)\n",
> - rom->name, rc, rom->romsize);
> + rom->name, rc, rom->datasize);
> goto err;
> }
> close(fd);
> @@ -637,16 +645,37 @@ int rom_add_blob(const char *name, const void *blob,
> size_t len,
> {
> Rom *rom;
>
> - rom = g_malloc0(sizeof(*rom));
> - rom->name = g_strdup(name);
> - rom->addr = addr;
> - rom->romsize = len;
> - rom->data = g_malloc0(rom->romsize);
> + rom = g_malloc0(sizeof(*rom));
> + rom->name = g_strdup(name);
> + rom->addr = addr;
> + rom->romsize = len;
> + rom->datasize = len;
> + rom->data = g_malloc0(rom->datasize);
> memcpy(rom->data, blob, len);
> rom_insert(rom);
> return 0;
> }
>
> +/* This function is specific for elf program because we don't need to
> allocate
> + * all the rom. We just allocate the first part and the rest is just zeros.
> This
> + * is why romsize and datasize are different. Also, this function seize the
> + * memory ownership of "data", so we don't have to allocate and copy the
> buffer.
> + */
> +int rom_add_elf_program(const char *name, void *data, size_t datasize,
> + size_t romsize, hwaddr addr)
> +{
> + Rom *rom;
> +
> + rom = g_malloc0(sizeof(*rom));
> + rom->name = g_strdup(name);
> + rom->addr = addr;
> + rom->datasize = datasize;
> + rom->romsize = romsize;
> + rom->data = data;
> + rom_insert(rom);
> + return 0;
> +}
> +
> int rom_add_vga(const char *file)
> {
> return rom_add_file(file, "vgaroms", 0, -1);
> @@ -668,7 +697,7 @@ static void rom_reset(void *unused)
> if (rom->data == NULL) {
> continue;
> }
> - cpu_physical_memory_write_rom(rom->addr, rom->data, rom->romsize);
> + cpu_physical_memory_write_rom(rom->addr, rom->data, rom->datasize);
> if (rom->isrom) {
> /* rom needs to be written only once */
> g_free(rom->data);
> @@ -756,13 +785,33 @@ int rom_copy(uint8_t *dest, hwaddr addr, size_t size)
>
> d = dest + (rom->addr - addr);
> s = rom->data;
> - l = rom->romsize;
> + l = rom->datasize;
>
> if ((d + l) > (dest + size)) {
> l = dest - d;
> }
>
> memcpy(d, s, l);
> +
> + if (rom->romsize > rom->datasize) {
> + /* If datasize is less than romsize, it means that we didn't
> + * allocate all the ROM because the trailing data are only zeros.
> + */
> +
> + d += l;
> + l = rom->romsize - rom->datasize;
> +
> + if ((d + l) > (dest + size)) {
> + /* Rom size doesn't fit in the destination area. Adjust to
> avoid
> + * overflow.
> + */
> + l = dest - d;
> + }
> +
> + if (l > 0) {
> + memset(d, 0x0, l);
> + }
> + }
> }
>
> return (d + l) - dest;
> diff --git a/hw/loader.h b/hw/loader.h
> index 5e61c95..0958f06 100644
> --- a/hw/loader.h
> +++ b/hw/loader.h
> @@ -27,6 +27,8 @@ int rom_add_file(const char *file, const char *fw_dir,
> hwaddr addr, int32_t bootindex);
> int rom_add_blob(const char *name, const void *blob, size_t len,
> hwaddr addr);
> +int rom_add_elf_program(const char *name, void *data, size_t datasize,
> + size_t romsize, hwaddr addr);
> int rom_load_all(void);
> void rom_set_fw(void *f);
> int rom_copy(uint8_t *dest, hwaddr addr, size_t size);
>