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关于.net:记一次-NET-某电商定向爬虫-内存碎片化分析

一:背景

1. 讲故事

上个月有位敌人 wx 找到我,说他的程序存在内存透露问题,寻求如何解决?如下图所示:

从截图中能够看出,这位敌人对 windbg 的操作还是有些相熟的,可能不足肯定的实操教训,所以用了几个命令之后就不晓得怎么排查上来了。

既然找到我,那就以我的集体教训在他的 dump 上持续剖析寻找罪魁祸首,闲话不多说,上 windbg 谈话。

二:Windbg 剖析

1. 真的存在内存透露吗?

追这个系列的敌人应该晓得,我无数次的用 !address -summary!eeheap -gc 这两个命令来判断以后的内存透露是属于托管层还是非托管层。


0:000> !address -summary

--- Usage Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
Free                                    358     7dfc`67f60000 (125.986 TB)           98.43%
<unknown>                              1087      203`88b6e000 (2.014 TB)  99.99%    1.57%
Image                                  1532        0`09f11000 (159.066 MB)   0.01%    0.00%
Heap                                    249        0`03453000 (52.324 MB)   0.00%    0.00%
Stack                                    66        0`01fc0000 (31.750 MB)   0.00%    0.00%
Other                                    10        0`001d1000 (1.816 MB)   0.00%    0.00%
TEB                                      22        0`0002c000 (176.000 kB)   0.00%    0.00%
PEB                                       1        0`00001000 (4.000 kB)   0.00%    0.00%

--- Type Summary (for busy) ------ RgnCount ----------- Total Size -------- %ofBusy %ofTotal
MEM_MAPPED                              183      200`00d06000 (2.000 TB)  99.30%    1.56%
MEM_PRIVATE                            1252        3`8d479000 (14.207 GB)   0.69%    0.01%
MEM_IMAGE                              1532        0`09f11000 (159.066 MB)   0.01%    0.00%

--- State Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
MEM_FREE                                358     7dfc`67f60000 (125.986 TB)           98.43%
MEM_RESERVE                             749      200`28a9b000 (2.001 TB)  99.33%    1.56%
MEM_COMMIT                             2218        3`6f5f5000 (13.740 GB)   0.67%    0.01%

0:000> !eeheap -gc
Number of GC Heaps: 1
generation 0 starts at 0x00000026DA8DA928
generation 1 starts at 0x00000026DA7FC348
generation 2 starts at 0x00000024C4691000
ephemeral segment allocation context: none
         segment             begin         allocated              size
00000024C4690000  00000024C4691000  00000024D468FF28  0xfffef28(268431144)
00000024EECF0000  00000024EECF1000  00000024FECF0000  0xffff000(268431360)
000000248D6F0000  000000248D6F1000  000000249D6EFEF8  0xfffeef8(268431096)
...
00000026D66D0000  00000026D66D1000  00000026DBA3CA30  0x536ba30(87472688)
Large object heap starts at 0x00000024D4691000
         segment             begin         allocated              size
00000024D4690000  00000024D4691000  00000024DC67C318  0x7feb318(134132504)
00000024E60F0000  00000024E60F1000  00000024EE0637C8  0x7f727c8(133638088)
0000002482140000  0000002482141000  000000248A08F338  0x7f4e338(133489464)
00000024A6770000  00000024A6771000  00000024AE76F6C0  0x7ffe6c0(134211264)
...
000000278E6D0000  000000278E6D1000  000000279635F2D0  0x7c8e2d0(130605776)
00000029233E0000  00000029233E1000  000000292AF672F8  0x7b862f8(129524472)
000000292B3E0000  000000292B3E1000  0000002931A5ED60  0x667dd60(107470176)
000000299B3E0000  000000299B3E1000  00000029A20095B0  0x6c285b0(113411504)
000000281E6D0000  000000281E6D1000  0000002825CD3F58  0x7602f58(123744088)
00000028266D0000  00000028266D1000  000000282D5CAD50  0x6ef9d50(116366672)
000000282E6D0000  000000282E6D1000  0000002833CA0880  0x55cf880(89979008)
00000029A33E0000  00000029A33E1000  00000029A684D300  0x346c300(54969088)
Total Size:              Size: 0x353f96d88 (14293757320) bytes.
------------------------------
GC Heap Size:    Size: 0x353f96d88 (14293757320) bytes.

从输入看,以后过程占用 MEM_COMMIT=13.7G,托管堆内存占用 14293757320 = 13.3G,很显著这属于简略模式的 托管内存透露 ,依据教训,托管堆上可能有什么大对象,这里用 !dumpheap -stat 命令。


0:000> !dumpheap -stat
Statistics:
              MT    Count    TotalSize Class Name
00007ff9ed6ea268  3956842     94964208 System.Collections.Generic.Dictionary`2+KeyCollection[[System.String, System.Private.CoreLib],[Serilog.Events.LogEventPropertyValue, Serilog]]
00007ff9ed5e6d28  3842435    166405016 Serilog.Parsing.MessageTemplateToken[]
00007ff9ed5e5e28  3842434    184436832 Serilog.Events.MessageTemplate
00007ff9ecccf090  4011012    203304420 System.Int32[]
00007ff9ed647078  3956849    253238336 Serilog.Events.LogEvent
00007ff9ed6e7b48  3956849    284893128 System.Collections.Generic.Dictionary`2[[System.String, System.Private.CoreLib],[Serilog.Events.LogEventPropertyValue, Serilog]]
00007ff9ed5e74e8  9259598    296307136 Serilog.Parsing.TextToken
00007ff9ed6471b0 12551808    301243392 Serilog.Events.ScalarValue
00007ff9ed6e8308  3956849    729078048 System.Collections.Generic.Dictionary`2+Entry[[System.String, System.Private.CoreLib],[Serilog.Events.LogEventPropertyValue, Serilog]][]
00007ff9eccb1e18 16546412   3987811940 System.String
00000024c3b8faf0    82904   7382993568      Free

我去,托管堆最大的对象竟然是 Free,大略占用 7.3G, 这就🐂👃了,不按套路出牌哈,为了更好的了解,先来简要解释下 free 对象。

2. 简略解释 free

其实简而言之,free 对象是被 gc 标记成已回收的闲暇块但并未提交给操作系统开释的对象,那怎么去证实呢?能够先到托管堆上找一个 free 块。


0:000> !dumpheap -type Free
         Address               MT     Size
00000024c4691000 00000024c3b8faf0       24 Free
00000024c46a2448 00000024c3b8faf0       24 Free
00000024c46b26d8 00000024c3b8faf0       40 Free
00000024c47e4418 00000024c3b8faf0       40 Free
00000024c4925680 00000024c3b8faf0       40 Free
00000024c49284a8 00000024c3b8faf0       64 Free
00000024c4947a90 00000024c3b8faf0      192 Free
00000024c4951f70 00000024c3b8faf0       48 Free         
000000249d6ea3a8 00000024c3b8faf0      640 Free
  1. 用 !do 命令查看是否标记为 free 块

0:000> !do 000000249d6ea3a8
Free Object
Size:        640(0x280) bytes
  1. 用 dc 看一下这个 free 块的内容,是否有 gc 回收的痕迹。

0:000> dc 000000249d6ea3a8 000000249d6ea3a8+0x280
00000024`9d6ea3a8  c3b8faf0 00000024 00000268 00000000  ....$...h.......
00000024`9d6ea3b8  9d6ea6d0 00000024 00000000 00000000  ..n.$...........
00000024`9d6ea3c8  ed3ae2b8 00007ff9 9d6ea3a8 00000024  ..:.......n.$...
00000024`9d6ea3d8  00000000 00000000 edcc9118 00007ff9  ................
00000024`9d6ea3e8  00000000 00000000 00000000 00000000  ................
00000024`9d6ea3f8  00000000 00000000 00000000 00000000  ................
00000024`9d6ea408  eeb07a50 00007ff9 9d6ea3c8 00000024  Pz........n.$...
00000024`9d6ea418  00000000 00000000 ef292ee8 00007ff9  ..........).....
00000024`9d6ea428  9d6ea408 00000024 00000000 00000000  ..n.$...........
...
00000024`9d6ea4a8  eeb0a158 00007ff9 9d6ea420 00000024  X....... .n.$...
00000024`9d6ea4b8  00000000 00000000 00000000 00000000  ................
00000024`9d6ea4c8  ef293818 00007ff9 9d6ea4a8 00000024  .8).......n.$...
00000024`9d6ea4d8  00000000 00000000 ee8357e0 00007ff9  .........W......
...
00000024`9d6ea508  eed37b40 00007ff9 00000000 00000000  @{..............
00000024`9d6ea518  00000000 00000000 00000000 00000000  ................
00000024`9d6ea528  c4699b48 00000024 00000000 00000000  H.i.$...........
00000024`9d6ea538  00000000 07000440 00000001 00000000  ....@...........
00000024`9d6ea548  00000000 00000000 00000000 00000000  ................
00000024`9d6ea558  00000000 00000000 ef2af6e0 00007ff9  ..........*.....
00000024`9d6ea568  00000000 00000000 00000000 00000000  ................
00000024`9d6ea578  00000000 00000000 c4699b48 00000024  ........H.i.$...
00000024`9d6ea588  00000000 00000000 00000000 07000400  ................
...
00000024`9d6ea628  ef2afd08                             ..*.

能够看到,这个 free 块生前是有一些残留的内容字符,好了,对 free 块有根本理解后,接下来咱们持续探索下。

3. 到底是什么阻止了 free 块的合并?

依照失常逻辑,大多 free 块会在 gc 回收完之后合并内存时,那些被清空后的 segment 会被操作系统开释的,但这个 dump 并没有,也就阐明这里有什么货色阻止了 free 块的合并,那到底是什么呢?有教训的敌人会说,能够察看下 gc 的句柄表,命令为 !gchandles -stat


0:000> !gchandles -stat
Statistics:
              MT    Count    TotalSize Class Name
...
00007ff9ed15c0f0     1008        72576 System.Reflection.Emit.DynamicResolver
00007ff9ecbf6618       38       409344 System.Object[]
Total 1784 objects

Handles:
    Strong Handles:       233
    Pinned Handles:       16
    Async Pinned Handles: 18
    Ref Count Handles:    1
    Weak Long Handles:    1327
    Weak Short Handles:   144
    Dependent Handles:    45

从输入看,这里并没有什么可疑的中央,那怎么办呢?实操教训多的话,这里还是有一些教训值得分享的,比方察看 free 在 heap 上的布局特色,往往就有重大发现。

4. 查看 free 块的布局特色

为了简化输入后果,我把范畴限定到 heap 上某一个 segment 上,比方这里的:00000029233E0000 000000292AF672F8,所以命令就是 !dumpheap 00000029233E0000 000000292AF672F8


0:000> !dumpheap 00000029233E0000  000000292AF672F8
         Address               MT     Size
00000029233e1000 00000024c3b8faf0  8291896 Free
0000002923bc9638 00007ff9eccb1e18   108448     
0000002923be3dd8 00000024c3b8faf0 29931248 Free
000000292586f4c8 00007ff9eccb1e18   301328     
00000029258b8dd8 00000024c3b8faf0 41384784 Free
0000002928030928 00007ff9eccb1e18   301328     
000000292807a238 00000024c3b8faf0  2542664 Free
00000029282e6e80 00007ff9eccb1e18   108448     
0000002928301620 00000024c3b8faf0 29915032 Free
0000002929f88db8 00007ff9eccb1e18   301328     
0000002929fd26c8 00000024c3b8faf0  2746688 Free
000000292a271008 00007ff9eccb1e18   291304     
000000292a2b81f0 00000024c3b8faf0  1019600 Free
000000292a3b10c0 00007ff9eccb1e18   108448     
000000292a3cb860 00000024c3b8faf0 10601048 Free
000000292ade7ab8 00007ff9eccb1e18   301328     
000000292ae313c8 00000024c3b8faf0   280808 Free
000000292ae75cb0 00007ff9eccb1e18   280854     
000000292aeba5c8 00000024c3b8faf0   416584 Free
000000292af20110 00007ff9eccb1e18   291304     

Statistics:
              MT    Count    TotalSize Class Name
00007ff9eccb1e18       10      2394118 System.String
00000024c3b8faf0       10    127130352      Free
Total 20 objects

真是一看吓一跳,free 和 object 呈交替状,这就是为什么 free 块不能被合并的真正起因,说实话这种教科书式的 内存碎片化 dump,真是可遇不可求,接下来就抽几个 free 之间的 object 对象,看看到底是被什么援用着导致 gc 回收不掉。

5. 寻找 object 的援用链

要想查看 object 到底被谁援用着,能够用 !gcroot 命令,这里我抽二个看看。


0:000> !gcroot 0000002923bc9638
Thread 1878:
    00000024C39BE4B0 00007FFA4C0B3522 System.Threading.Tasks.Task.SpinThenBlockingWait(Int32, System.Threading.CancellationToken) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2922]
        rbp+10: 00000024c39be520
            ->  00000024C48AD6E0 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions+<RunAsync>d__4, Microsoft.Extensions.Hosting.Abstractions]]
            ->  00000024C48AD200 Microsoft.Extensions.Hosting.Internal.Host
            ->  00000024C48AC538 Microsoft.Extensions.Logging.Logger`1[[Microsoft.Extensions.Hosting.Internal.Host, Microsoft.Extensions.Hosting]]
            ->  00000024C48AC658 Microsoft.Extensions.Logging.Logger
            ->  00000024C48AC680 Microsoft.Extensions.Logging.LoggerInformation[]
            ->  00000024C48AC6E0 Serilog.Extensions.Logging.SerilogLogger
            ->  00000024C48AC808 Serilog.Core.Logger
            ->  00000024C48AC760 Serilog.Core.Logger
            ->  00000024C47AD468 Serilog.Core.Logger
            ->  00000024C47ABF08 Serilog.Core.Sinks.SafeAggregateSink
            ->  00000024C47ABF20 Serilog.Core.ILogEventSink[]
            ->  00000024C479C548 Serilog.Sinks.Grafana.Loki.LokiSink
            ->  00000024C479C778 Serilog.Sinks.Grafana.Loki.Infrastructure.BoundedQueue`1[[Serilog.Events.LogEvent, Serilog]]
            ->  00000024C479C7B8 System.Collections.Generic.Queue`1[[Serilog.Events.LogEvent, Serilog]]
            ->  00000026E8C1A800 Serilog.Events.LogEvent[]
            ->  00000026148D3308 Serilog.Events.LogEvent
            ->  00000026148D4EF0 Serilog.Events.MessageTemplate
            ->  0000002923BC9638 System.String

Found 1 unique roots (run '!gcroot -all' to see all roots).

0:000> !gcroot 000000292586f4c8
Thread 1878:
    00000024C39BE4B0 00007FFA4C0B3522 System.Threading.Tasks.Task.SpinThenBlockingWait(Int32, System.Threading.CancellationToken) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2922]
        rbp+10: 00000024c39be520
            ->  00000024C48AD6E0 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions+<RunAsync>d__4, Microsoft.Extensions.Hosting.Abstractions]]
            ->  00000024C48AD200 Microsoft.Extensions.Hosting.Internal.Host
            ->  00000024C48AC538 Microsoft.Extensions.Logging.Logger`1[[Microsoft.Extensions.Hosting.Internal.Host, Microsoft.Extensions.Hosting]]
            ->  00000024C48AC658 Microsoft.Extensions.Logging.Logger
            ->  00000024C48AC680 Microsoft.Extensions.Logging.LoggerInformation[]
            ->  00000024C48AC6E0 Serilog.Extensions.Logging.SerilogLogger
            ->  00000024C48AC808 Serilog.Core.Logger
            ->  00000024C48AC760 Serilog.Core.Logger
            ->  00000024C47AD468 Serilog.Core.Logger
            ->  00000024C47ABF08 Serilog.Core.Sinks.SafeAggregateSink
            ->  00000024C47ABF20 Serilog.Core.ILogEventSink[]
            ->  00000024C479C548 Serilog.Sinks.Grafana.Loki.LokiSink
            ->  00000024C479C778 Serilog.Sinks.Grafana.Loki.Infrastructure.BoundedQueue`1[[Serilog.Events.LogEvent, Serilog]]
            ->  00000024C479C7B8 System.Collections.Generic.Queue`1[[Serilog.Events.LogEvent, Serilog]]
            ->  00000026E8C1A800 Serilog.Events.LogEvent[]
            ->  0000002614BB7AC8 Serilog.Events.LogEvent
            ->  0000002616D3CC40 Serilog.Events.MessageTemplate
            ->  000000292586F4C8 System.String

Found 1 unique roots (run '!gcroot -all' to see all roots).

从援用链看,这些 object 都是通过 Serilog 日志组件发送给 Grafana.Loki,通过对援用链对象的追踪,我发现 System.Collections.Generic.Queue 有重大问题,截图如下:

对,这个 queue 竟然有 395w 的积压,到底积压了什么货色,能够用 !wdo 看一下 string 内容。

看样子这是一个失败重试,剖析到这里思路大略就清晰了,就是 Grafana.Loki 或者 Serilog 组件出了什么问题,导致日志发送不到 Loki 中或者发送速度过慢,而后一直的积压所致,接下来把剖析到的这些信息和敌人做了一个沟通,截图如下:

三:总结

本次内存碎片化的次要起因在于 Serilog 对接 Loki 的过程中产生的 395w 的 queue 积压所致,但我也只能剖析到这里了,至于为什么有积压,这个还得敌人进一步调试剖析,我置信这个问题很快就能失去解决💪💪💪

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