jemalloc存储块(region、run、chunk)

jemalloc中按存储单元的块大小分，有region、run、chunk三种存储块。

最小的单元是region，它的大小是8字节~14KB，1个或多个相同大小的region组成一个run。

run的大小必须是页(4kB)的整数倍，相同大小region对应的run的大小总是相同的，多个run组成一个chunk。

chunk的大小固定是2M（或4M，可配置）。

相关代码：

arena_bin_info_t    arena_bin_info[NBINS];

static void
bin_info_init(void)
{
    arena_bin_info_t *bin_info;

#define    BIN_INFO_INIT_bin_yes(index, size)                \
    bin_info = &arena_bin_info[index];                    bin_info->reg_size = size;                        bin_info_run_size_calc(bin_info);                    bitmap_info_init(&bin_info->bitmap_info, bin_info->nregs);
#define    BIN_INFO_INIT_bin_no(index, size)
#define    SC(index, lg_grp, lg_delta, ndelta, bin, lg_delta_lookup)    \
    BIN_INFO_INIT_bin_##bin(index, (ZU(1)<<lg_grp) + (ZU(ndelta)<<lg_delta))
    SIZE_CLASSES
#undef BIN_INFO_INIT_bin_yes
#undef BIN_INFO_INIT_bin_no
#undef SC
}

gdb中打印arena_bin_info：

(gdb) p je_arena_bin_info
$353 = {{
    reg_size = 8,
    redzone_size = 0,
    reg_interval = 8,
    run_size = 4096,
    nregs = 512,
    bitmap_info = {
      nbits = 512,
      ngroups = 8
    },
    reg0_offset = 0
  }, {
    reg_size = 16,
    redzone_size = 0,
    reg_interval = 16,
    run_size = 4096,
    nregs = 256,
    bitmap_info = {
      nbits = 256,
      ngroups = 4
    },
    reg0_offset = 0
  }, {
    reg_size = 32,
    redzone_size = 0,
    reg_interval = 32,
    run_size = 4096,
    nregs = 128,
    bitmap_info = {
      nbits = 128,
      ngroups = 2
    },
    reg0_offset = 0
  }, {
     ...
  }, {
    reg_size = 12288,
    redzone_size = 0,
    reg_interval = 12288,
    run_size = 12288,
    nregs = 1,
    bitmap_info = {
      nbits = 1,
      ngroups = 1
    },
    reg0_offset = 0
  }, {
    reg_size = 14336,
    redzone_size = 0,
    reg_interval = 14336,
    run_size = 28672,
    nregs = 2,
    bitmap_info = {
      nbits = 2,
      ngroups = 1
    },
    reg0_offset = 0
  }}

region、run、chunk之间的位置关系如下：