前言
对服务端程序来说, 内存泄漏是经常会面临的问题. 使用erlang的情况下, 不用程序员手动管理内存. 如果不写c driver, 一般的内存问题还是很容易定位的. 这篇blog对常见的内存泄漏类型, 排查手段做个小结.
内存泄漏类型
process泄漏
如果没有etop
iex(xxxx@xxxx.)1> :erlang.system_info(:process_count)
5369可以通过process_count来获取erlang vm中已分配的process数量. 若process数量和业务实际需要不吻合, 则需要排查.
消息堆积
iex(xxxx@xxxx.)5> spawn fn -> :etop.start([sort: :msg_q]) end
#PID<0.6255.1>
========================================================================================
'xxxx@xxxx.' 03:04:46
Load: cpu 0 Memory: total 147234 binary 2839
procs 5371 processes 59008 code 42641
runq 0 atom 1722 ets 8239
Pid Name or Initial Func Time Reds Memory MsgQ Current Function
----------------------------------------------------------------------------------------
<7796.0.0> init '-' 339058 29540 0 init:loop/1
<7796.1.0> erts_code_purger '-' 479850 285160 0 erts_code_purger:wai
<7796.2.0> erts_literal_area_co '-' 337591 2688 0 erts_literal_area_co
<7796.3.0> erts_dirty_process_s '-' 37924 2688 0 erts_dirty_process_s一般消息堆积都会伴随着memory增长, 不管是sort by msg_q 或 memory, 都很容易发现问题.
如果没有etop
iex(xxxx@xxxx.)8> Enum.map(:erlang.processes(), fn proc -> {:erlang.process_info(proc, :message_queue_len), proc} end) |> Enum.sort(fn({{_, a}, _}, {{_, b}, _}) -> a > b end) |> List.first
{{:message_queue_len, 0}, #PID<0.32638.0>}ets表泄漏
找出占用最多内存的ets表
iex(7)> :ets.all() |> Enum.map(fn ets_name -> {:ets.info(ets_name, :memory), ets_name} end) |> Enum.sort(fn a, b -> a > b end)
[
{18002942, :test},
{41940, #Reference<0.3983585142.1897791489.87703>},
...
]整体内存分析
:erlang.memory 可以一眼看出是否ets表存在泄漏
值得注意的是, 大于64bit的binary, 会在:erlang.memory的binary项体现. 不会计入ets项中.
65bit
iex(1)> :ets.new(:test, [:public, :named_table])
:test
iex(2)> :erlang.memory
[
total: 23688632,
processes: 4940400,
processes_used: 4939456,
system: 18748232,
atom: 463465,
atom_used: 442288,
binary: 27872,
code: 8462310,
ets: 589664
]
iex(3)> for num <- 1..1000000 do
...(3)> :ets.insert(:test, {num, :crypto.strong_rand_bytes(65)})
...(3)> end
[true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, ...]
iex(4)> :erlang.memory
[
total: 284511736,
processes: 33626760,
processes_used: 33625816,
system: 250884976,
atom: 463465,
atom_used: 446381,
binary: 112090520,
code: 8553627,
ets: 120619384
]64bit
iex(1)> :ets.new(:test, [:public, :named_table])
:test
iex(2)> :erlang.memory
[
total: 23569856,
processes: 4778728,
processes_used: 4777784,
system: 18791128,
atom: 463465,
atom_used: 442288,
binary: 70736,
code: 8462310,
ets: 589680
]
iex(3)> for num <- 1..1000000 do
...(3)> :ets.insert(:test, {num, :crypto.strong_rand_bytes(64)})
...(3)> end
[true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, true, true,
true, true, true, true, true, true, true, true, true, true, true, ...]
iex(4)> :erlang.memory
[
total: 204325192,
processes: 33373520,
processes_used: 33372576,
system: 170951672,
atom: 463465,
atom_used: 447944,
binary: 39168,
code: 8653586,
ets: 152623976
]数据过大
首先, 应该能估算出业务大致的内存占用. 可以通过process_info, 找出可疑的进程.
iex(11)> :erlang.process_info(:ets.info(:test, :owner), :memory)
{:memory, 28693220}通过:sys.get_state可以发现一些逻辑错误造成的, list/map无限增长的bug.
iex(xxxxx@xxxxx.)13> :sys.get_state(:erlang.list_to_pid('<0.2362.0>'))
{:state, {:local, :prometheus_sup}, :one_for_one, {[], %{}}, :undefined, 5, 1,
[], 0, :prometheus_sup, []}内存估算
https://github.com/okeuday/erlang_term
http://erlang.org/doc/efficiency_guide/advanced.html#id68923
一些源码的阅读记录
elixir数据类型
- integer
- float
- boolean
- atom
- string
- list
- tuple
Map MapSet, func, nil, ets?
#if ET_DEBUG
ERTS_GLB_INLINE unsigned tag_val_def(Wterm x, const char *file, unsigned line)
#else
ERTS_GLB_INLINE unsigned tag_val_def(Wterm x)
#define file __FILE__
#define line __LINE__
#endif
{
static char *msg = "tag_val_def error";
switch (x & _TAG_PRIMARY_MASK) {
case TAG_PRIMARY_LIST:
ET_ASSERT(_list_precond(x),file,line);
return LIST_DEF;
case TAG_PRIMARY_BOXED: {
Eterm hdr = *boxed_val(x);
ET_ASSERT(is_header(hdr),file,line);
switch ((hdr & _TAG_HEADER_MASK) >> _TAG_PRIMARY_SIZE) {
case (_TAG_HEADER_ARITYVAL >> _TAG_PRIMARY_SIZE): return TUPLE_DEF;
case (_TAG_HEADER_POS_BIG >> _TAG_PRIMARY_SIZE): return BIG_DEF;
case (_TAG_HEADER_NEG_BIG >> _TAG_PRIMARY_SIZE): return BIG_DEF;
case (_TAG_HEADER_REF >> _TAG_PRIMARY_SIZE): return REF_DEF;
case (_TAG_HEADER_FLOAT >> _TAG_PRIMARY_SIZE): return FLOAT_DEF;
case (_TAG_HEADER_EXPORT >> _TAG_PRIMARY_SIZE): return EXPORT_DEF;
case (_TAG_HEADER_FUN >> _TAG_PRIMARY_SIZE): return FUN_DEF;
case (_TAG_HEADER_EXTERNAL_PID >> _TAG_PRIMARY_SIZE): return EXTERNAL_PID_DEF;
case (_TAG_HEADER_EXTERNAL_PORT >> _TAG_PRIMARY_SIZE): return EXTERNAL_PORT_DEF;
case (_TAG_HEADER_EXTERNAL_REF >> _TAG_PRIMARY_SIZE): return EXTERNAL_REF_DEF;
case (_TAG_HEADER_MAP >> _TAG_PRIMARY_SIZE): return MAP_DEF;
case (_TAG_HEADER_REFC_BIN >> _TAG_PRIMARY_SIZE): return BINARY_DEF;
case (_TAG_HEADER_HEAP_BIN >> _TAG_PRIMARY_SIZE): return BINARY_DEF;
case (_TAG_HEADER_SUB_BIN >> _TAG_PRIMARY_SIZE): return BINARY_DEF;
case (_TAG_HEADER_BIN_MATCHSTATE >> _TAG_PRIMARY_SIZE): return MATCHSTATE_DEF;
}
break;
}
case TAG_PRIMARY_IMMED1: {
switch ((x & _TAG_IMMED1_MASK) >> _TAG_PRIMARY_SIZE) {
case (_TAG_IMMED1_PID >> _TAG_PRIMARY_SIZE): return PID_DEF;
case (_TAG_IMMED1_PORT >> _TAG_PRIMARY_SIZE): return PORT_DEF;
case (_TAG_IMMED1_IMMED2 >> _TAG_PRIMARY_SIZE): {
switch ((x & _TAG_IMMED2_MASK) >> _TAG_IMMED1_SIZE) {
case (_TAG_IMMED2_ATOM >> _TAG_IMMED1_SIZE): return ATOM_DEF;
case (_TAG_IMMED2_NIL >> _TAG_IMMED1_SIZE): return NIL_DEF;
}
break;
}
case (_TAG_IMMED1_SMALL >> _TAG_PRIMARY_SIZE): return SMALL_DEF;
}
break;
}
}
erl_assert_error(msg, __FUNCTION__, file, line);
#undef file
#undef line
}
#endifinteger
small integer
可以看到, erlang区分了大小整数, 小整数根据64/32系统不同, 使用了 N-4 bit字节. 最低位为0xF, 即0b1111
#define is_integer(x) (is_small(x) || is_big(x))
/* fixnum ("small") access methods */
#if defined(ARCH_64)
#define SMALL_BITS (64-4)
#define SMALL_DIGITS (17)
#else
#define SMALL_BITS (28)
#define SMALL_DIGITS (8)
#endif
#define MAX_SMALL ((SWORD_CONSTANT(1) << (SMALL_BITS-1))-1)
#define MIN_SMALL (-(SWORD_CONSTANT(1) << (SMALL_BITS-1)))
#define _TAG_IMMED1_SMALL ((0x3 << _TAG_PRIMARY_SIZE) | TAG_PRIMARY_IMMED1)
#define make_small(x) (((Uint)(x) << _TAG_IMMED1_SIZE) + _TAG_IMMED1_SMALL)
#define is_small(x) (((x) & _TAG_IMMED1_MASK) == _TAG_IMMED1_SMALL)尤其是make_small宏.
#define make_small(x) (((Uint)(x) << _TAG_IMMED1_SIZE) + _TAG_IMMED1_SMALL)故, 小整形占用64/32 bit空间.
big integer
最低位是否为0, boxed?
#define make_big(x) make_boxed((x))
#define make_boxed(x) _ET_APPLY(make_boxed,(x))
#define TAG_PRIMARY_BOXED 0x2
#define _unchecked_make_boxed(x) ((Uint)(x) + TAG_PRIMARY_BOXED)
#define _TAG_PRIMARY_MASK 0x3
#define _is_not_boxed(x) ((x) & (_TAG_PRIMARY_MASK-TAG_PRIMARY_BOXED))atom
#define make_atom(x) ((Eterm)(((x) << _TAG_IMMED2_SIZE) + _TAG_IMMED2_ATOM))
#define is_atom(x) (((x) & _TAG_IMMED2_MASK) == _TAG_IMMED2_ATOM)nil
一个固定uint值.
#define NIL ((~((Uint) 0) << _TAG_IMMED2_SIZE) | _TAG_IMMED2_NIL)ets
map
flat_map
若size小于MAP_SMALL_MAP_LIMIT(32), 大部分的map都属于flat_map.
erts_produce_heap(factory, 3 + 1 + (2 * n), 0);
ERTS_GLB_INLINE Eterm *1 =
erts_produce_heap(ErtsHeapFactory* factory, Uint need, Uint xtra)
{
Eterm* res;
ASSERT((unsigned int)factory->mode > (unsigned int)FACTORY_CLOSED);
if (factory->hp + need > factory->hp_end) {
erts_reserve_heap__(factory, need, xtra);
}
res = factory->hp;
factory->hp += need;
return res;
}即分配4+2*n wordsize byte内存.
iex(1)> :erlang.system_info(:wordsize)
8
iex(2)> :erts_debug.flat_size(%{})
4
iex(3)> :erlang_term.byte_size(%{})
# 这是因为erlang term本身指针有8字节. 加对上的32字节, 共40字节.
40
iex(4)> :erts_debug.flat_size(%{1 => 1})
6
iex(5)> :erlang_term.byte_size(%{1 => 1})
56
iex(6)> :erts_debug.flat_size(%{1 => 1, 2 => 2})
8