一：背景
1. 讲故事
上个月有位朋友找到我，说他的程序存在内存溢出情况，寻求如何解决。
要解决还得通过 windbg 分析啦。
二：Windbg 分析
1. 为什么会内存溢出
大家都知道内存溢出对应着 .NET 中的 OutOfMemoryException 异常，这种异常有可能是托管代码手工抛出的，也有可能是CLR层面抛出的，言外之意就是可以通过两种方式排查。
- 托管线程是否挂载着异常？
0:000> !t
ThreadCount: 23
UnstartedThread: 0
BackgroundThread: 5
PendingThread: 0
DeadThread: 17
Hosted Runtime: no
Lock
ID OSID ThreadOBJ State GC Mode GC Alloc Context Domain Count Apt Exception
0 1 362c 00fac868 26020 Preemptive 7ED701A0:00000000 00fa6b60 0 STA
5 2 2d70 00fbeba0 2b220 Preemptive 7EBA7AC0:00000000 00fa6b60 0 MTA (Finalizer)
7 3 3264 061c8890 102a220 Preemptive 00000000:00000000 00fa6b60 0 MTA (Threadpool Worker)
17 15 3f98 19682b90 202b220 Preemptive 7EBB0830:00000000 00fa6b60 0 MTA
XXXX 16 0 2845fb00 35820 Preemptive 00000000:00000000 00fa6b60 0 Ukn
18 14 a7c 2842b1c8 202b220 Preemptive 00000000:00000000 00fa6b60 0 MTA
XXXX 6 0 2c9b3778 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 18 0 288a1318 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 23 0 288a22f0 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 10 0 2ccf3550 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 21 0 288a1860 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 12 0 288a1da8 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 11 0 2c993640 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 8 0 2ccf3a98 35820 Preemptive 00000000:00000000 00fa6b60 0 Ukn
XXXX 9 0 2ccf2030 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 7 0 2c9aed88 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 26 0 28898308 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 25 0 2c492c68 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 4 0 2c993b88 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 20 0 2c9af2d0 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 17 0 2c9afd60 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
XXXX 24 0 2c9b1280 1039820 Preemptive 00000000:00000000 00fa6b60 0 Ukn (Threadpool Worker)
23 22 2658 2c9b02a8 1029220 Preemptive 7ED5BFF8:00000000 00fa6b60 0 MTA (Threadpool Worker)
从输出信息看，这些线程并没有挂载任何托管异常，我去。。。
- 是否在 CLR 上抛出
这主要是看 托管堆(heap) 上的内存分配或者gc回收造成的内存不足，可以用 !ao 命令。
0:000> !ao
There was no managed OOM due to allocations on the GC heap
从输出信息看也没有任何异常，尴尬了???。。。 尼玛，那到底是因为什么呢？
2. 探索溢出原因
出现这种尴尬情况，我只能怀疑生成这个dump的时候并没有get到那个点，或者是我的知识边界有限，不过天无绝人之路，不在那个 点 也肯定在那个 点 附近，对吧，接下来用 !address -summary 看一下内存使用的归类信息。
0:000> !address -summary
--- Usage Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
<unknown> 1520 4c185000 ( 1.189 GB) 65.57% 59.45%
Image 4306 1f140000 ( 497.250 MB) 26.78% 24.28%
Free 1133 bf17000 ( 191.090 MB) 9.33%
Heap 617 7626000 ( 118.148 MB) 6.36% 5.77%
Stack 72 1740000 ( 23.250 MB) 1.25% 1.14%
Other 34 7b000 ( 492.000 kB) 0.03% 0.02%
TEB 24 30000 ( 192.000 kB) 0.01% 0.01%
PEB 1 3000 ( 12.000 kB) 0.00% 0.00%
--- Type Summary (for busy) ------ RgnCount ----------- Total Size -------- %ofBusy %ofTotal
MEM_MAPPED 549 34b60000 ( 843.375 MB) 45.42% 41.18%
MEM_PRIVATE 1718 20424000 ( 516.141 MB) 27.80% 25.20%
MEM_IMAGE 4307 1f155000 ( 497.332 MB) 26.78% 24.28%
--- State Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
MEM_COMMIT 4904 66ddd000 ( 1.607 GB) 88.64% 80.37%
MEM_RESERVE 1670 d2fc000 ( 210.984 MB) 11.36% 10.30%
MEM_FREE 1133 bf17000 ( 191.090 MB) 9.33%
--- Protect Summary (for commit) - RgnCount ----------- Total Size -------- %ofBusy %ofTotal
PAGE_READONLY 2272 382cf000 ( 898.809 MB) 48.41% 43.89%
PAGE_READWRITE 1572 1eead000 ( 494.676 MB) 26.64% 24.15%
PAGE_EXECUTE_READ 218 dd59000 ( 221.348 MB) 11.92% 10.81%
PAGE_WRITECOPY 449 133e000 ( 19.242 MB) 1.04% 0.94%
PAGE_EXECUTE_READWRITE 188 ab4000 ( 10.703 MB) 0.58% 0.52%
PAGE_NOACCESS 156 9c000 ( 624.000 kB) 0.03% 0.03%
PAGE_READWRITE | PAGE_GUARD 48 78000 ( 480.000 kB) 0.03% 0.02%
PAGE_READWRITE | PAGE_WRITECOMBINE 1 2000 ( 8.000 kB) 0.00% 0.00%
--- Largest Region by Usage ----------- Base Address -------- Region Size ----------
<unknown> 1d200000 a001000 ( 160.004 MB)
Image fed1000 36e4000 ( 54.891 MB)
Free 33dfe000 1082000 ( 16.508 MB)
Heap 3da84000 a1b000 ( 10.105 MB)
Stack 1a10000 fd000 (1012.000 kB)
Other 7fa40000 33000 ( 204.000 kB)
TEB a4c000 3000 ( 12.000 kB)
PEB a3d000 3000 ( 12.000 kB)
从上面的 MEM_COMMIT=1.607 GB 80.37% 信息看，当前内存占用 1.6G，占比 80.37%，可以看出它受到了一个 2G内存 的限制，而且从 !t 输出中的内存地址看，当前是 32bit 程序，所以这是一个经典的: 64系统跑着32位程序被2G内存限制 的问题。
3. 如何突破 2G 限制
要寻找答案，还得看最权威的 MSDN:
https://docs.microsoft.com/en-us/windows/win32/memory/memory-limits-for-windows-releases?redirectedfrom=MSDN
破局 还得设置程序的 IMAGE_FILE_LARGE_ADDRESS_AWARE 标记。
关于具体怎么设置，我找了三种方法。
- 使用 LargeAddressAware 安装包
参见 github：
https://github.com/KirillOsenkov/LargeAddressAware
- 使用 editbin
可以在 vs 的生成事件中输入 editbin /largeaddressaware $(TargetPath)。
- 使用代码方式
这种可以直接给生成好的 exe 增加 LargeAddressAware 标记，除了标记，还能检测，??
using System;
using System.IO;
namespace PEFile
{
public class LargeAddressAware
{
public static bool IsLargeAddressAware(string filePath)
{
bool isLargeAddressAware = false;
PrepareStream(filePath, (stream, binaryReader) => isLargeAddressAware = (binaryReader.ReadInt16() & 0x20) != 0);
return isLargeAddressAware;
}
public static void SetLargeAddressAware(string filePath)
{
PrepareStream(filePath, (stream, binaryReader) =>
{
var value = binaryReader.ReadInt16();
if ((value & 0x20) == 0)
{
value = (short)(value | 0x20);
stream.Position -= 2;
var binaryWriter = new BinaryWriter(stream);
binaryWriter.Write(value);
binaryWriter.Flush();
}
});
}
private static void PrepareStream(string filePath, Action<Stream, BinaryReader> action)
{
using (var stream = new FileStream(filePath, FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
{
if (stream.Length < 0x3C)
{
return;
}
var binaryReader = new BinaryReader(stream);
// MZ header
if (binaryReader.ReadInt16() != 0x5A4D)
{
return;
}
stream.Position = 0x3C;
var peHeaderLocation = binaryReader.ReadInt32();
stream.Position = peHeaderLocation;
// PE header
if (binaryReader.ReadInt32() != 0x4550)
{
return;
}
stream.Position += 0x12;
action(stream, binaryReader);
}
}
}
}
更多办法参考：
https://stackoverflow.com/questions/639540/how-much-memory-can-a-32-bit-process-access-on-a-64-bit-operating-system
三：总结
总的来说，2G 内存限制 是一个 32bit 程序所必须面对的问题，知道了就好解决了，最后有一个问题要解释下，为什么 commit 内存高达 1.6G，这是因为医疗类的软件，大多是 FastReport + DevExpress 这些重量级的经典搭配以及大量的图片资源占用了太多 native memory。
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