{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"現代高級編程語言管理內存的方式分爲兩種：自動和手動，像C、C++ 等編程語言使用手動管理內存的方式，工程師編寫代碼過程中需要主動申請或者釋放內存；而 PHP、Java 和 Go 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main\n\ntype smallStruct struct {\n a, b int64\n c, d float64\n}\n\nfunc main() {\n smallAllocation()\n}\n\n//go:noinline\nfunc smallAllocation() *smallStruct {\n return 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去獲取。"},{"type":"codeinline","content":[{"type":"text","text":"mcentral"}]},{"type":"text","text":"被所有的工作線程共同享有，存在多個"},{"type":"codeinline","content":[{"type":"text","text":"goroutine"}]},{"type":"text","text":"競爭的情況，因此從"},{"type":"codeinline","content":[{"type":"text","text":"mcentral"}]},{"type":"text","text":"獲取資源時需要加鎖。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"mcentral"}]},{"type":"text","text":"的定義如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":""},"content":[{"type":"text","text":"//runtime/mcentral.go\n\ntype mcentral struct {\n // 互斥鎖\n lock mutex \n \n // 規格\n sizeclass int32 \n \n // 尚有空閒object的mspan鏈表\n nonempty mSpanList \n \n // 沒有空閒object的mspan鏈表，或者是已被mcache取走的msapn鏈表\n empty mSpanList \n \n // 已累計分配的對象個數\n nmalloc 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的內存。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ac/acf45ff994e25f720e5695c0116eb02c.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果 "},{"type":"codeinline","content":[{"type":"text","text":"arena"}]},{"type":"text","text":" 區域沒有足夠的空間，會調用 "},{"type":"link","attrs":{"href":"https://github.com/golang/go/blob/6dd11bcb35cba37f5994c1b9aaaf7d2dc13fd7cf/src/runtime/malloc.go#L617","title":""},"content":[{"type":"text","text":"runtime.mheap.sysAlloc"}]},{"type":"text","text":" 從操作系統中申請更多的內存。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"大於32KB內存塊的分配策略"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go沒法使用工作線程的本地緩存"},{"type":"codeinline","content":[{"type":"text","text":"mcache"}]},{"type":"text","text":"和全局中心緩存"},{"type":"codeinline","content":[{"type":"text","text":"mcentral"}]},{"type":"text","text":"上管理超過32KB的內存分配，所以對於那些超過32KB的內存申請，會直接從堆上("},{"type":"codeinline","content":[{"type":"text","text":"mheap"}]},{"type":"text","text":")上分配對應的數量的內存頁（每頁大小是8KB）給程序。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5a/5a1bddc841eb177b0a6c280b76279f79.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"總結"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們把內存分配管理涉及的所有概念串起來，可以勾畫出Go內存管理的一個全局視圖："}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5f/5f19bbede074d83d2d28295cfb9500ab.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go語言的內存分配非常複雜，這個文章從一個比較粗的角度來看Go的內存分配，並沒有深入細節。一般而言，瞭解它的原理，到這個程度也就可以了（應付面試）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"總結起來關於Go內存分配管理的策略有如下幾點："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go在程序啓動時，會向操作系統申請一大塊內存，由"},{"type":"codeinline","content":[{"type":"text","text":"mheap"}]},{"type":"text","text":"結構全局管理。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go內存管理的基本單元是"},{"type":"codeinline","content":[{"type":"text","text":"mspan"}]},{"type":"text","text":"，每種"},{"type":"codeinline","content":[{"type":"text","text":"mspan"}]},{"type":"text","text":"可以分配特定大小的"},{"type":"codeinline","content":[{"type":"text","text":"object"}]},{"type":"text","text":"。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"mcache"}]},{"type":"text","text":", 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Memory Management and Allocation"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://juejin.im/post/6844903795739082760#heading-7","title":""},"content":[{"type":"text","text":"圖解Go語言內存分配"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://draveness.me/golang/docs/part3-runtime/ch07-memory/golang-memory-allocator/","title":""},"content":[{"type":"text","text":"內存分配器"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"感謝你閱讀我的文章，微信搜索公衆號「網管叨bi叨」第一時間獲取更多原創圖解Go語言原理的文章。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}
白話Go語言內存管理--內存分配原理
{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"現代高級編程語言管理內存的方式分爲兩種：自動和手動，像C、C++ 等編程語言使用手動管理內存的方式，工程師編寫代碼過程中需要主動申請或者釋放內存；而 PHP、Java 和 Go 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main\n\ntype smallStruct struct {\n a, b int64\n c, d float64\n}\n\nfunc main() {\n smallAllocation()\n}\n\n//go:noinline\nfunc smallAllocation() *smallStruct {\n return &smallStruct{}\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數上面的註釋"},{"type":"codeinline","content":[{"type":"text","text":"//go:noinline"}]},{"type":"text","text":"將禁止"},{"type":"codeinline","content":[{"type":"text","text":"Go"}]},{"type":"text","text":"對該函數進行內聯，這樣"},{"type":"codeinline","content":[{"type":"text","text":"main"}]},{"type":"text","text":"函數就會使用"},{"type":"codeinline","content":[{"type":"text","text":"smallAllocation"}]},{"type":"text","text":"函數返回的指針變量，因爲被多個函數使用，返回的這個變量將被分配到堆上。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"關於內聯的概念之前的文章有說過："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"內聯是一種手動或編譯器優化，用於將簡短函數的調用替換爲函數體本身。這麼做的原因是它可以消除函數調用本身的開銷，也使得編譯器能更高效地執行其他的優化策略。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以如果上面的例子不干預編譯器的話，編譯器通過內聯將"},{"type":"codeinline","content":[{"type":"text","text":"smallAllocation"}]},{"type":"text","text":"函數體裏的內容直接放到"},{"type":"codeinline","content":[{"type":"text","text":"main"}]},{"type":"text","text":"函數裏，這樣就不會產生"},{"type":"codeinline","content":[{"type":"text","text":"smallAllocation"}]},{"type":"text","text":"這個函數的調用了，所有的變量都是"},{"type":"codeinline","content":[{"type":"text","text":"main"}]},{"type":"text","text":"函數內這個範圍使用的，也就不在需要將變量往堆上分配了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"繼續說上面那個例子，通過逃逸分析命令 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main.go"},{"type":"text","text":"，可以顯示該程序的彙編代碼，也可以明確地向我們展示內存的分配："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"shell"},"content":[{"type":"text","text":"0x001d 00029 (main.go:10) LEAQ type.\"\".smallStruct(SB), AX\n0x0024 00036 (main.go:10) PCDATA $2, $0\n0x0024 00036 (main.go:10) MOVQ AX, (SP)\n0x0028 00040 (main.go:10) CALL 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從操作系統中申請更多的內存。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"大於32KB內存塊的分配策略"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go沒法使用工作線程的本地緩存"},{"type":"codeinline","content":[{"type":"text","text":"mcache"}]},{"type":"text","text":"和全局中心緩存"},{"type":"codeinline","content":[{"type":"text","text":"mcentral"}]},{"type":"text","text":"上管理超過32KB的內存分配，所以對於那些超過32KB的內存申請，會直接從堆上("},{"type":"codeinline","content":[{"type":"text","text":"mheap"}]},{"type":"text","text":")上分配對應的數量的內存頁（每頁大小是8KB）給程序。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5a/5a1bddc841eb177b0a6c280b76279f79.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"總結"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們把內存分配管理涉及的所有概念串起來，可以勾畫出Go內存管理的一個全局視圖："}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5f/5f19bbede074d83d2d28295cfb9500ab.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go語言的內存分配非常複雜，這個文章從一個比較粗的角度來看Go的內存分配，並沒有深入細節。一般而言，瞭解它的原理，到這個程度也就可以了（應付面試）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"總結起來關於Go內存分配管理的策略有如下幾點："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go在程序啓動時，會向操作系統申請一大塊內存，由"},{"type":"codeinline","content":[{"type":"text","text":"mheap"}]},{"type":"text","text":"結構全局管理。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go內存管理的基本單元是"},{"type":"codeinline","content":[{"type":"text","text":"mspan"}]},{"type":"text","text":"，每種"},{"type":"codeinline","content":[{"type":"text","text":"mspan"}]},{"type":"text","text":"可以分配特定大小的"},{"type":"codeinline","content":[{"type":"text","text":"object"}]},{"type":"text","text":"。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"mcache"}]},{"type":"text","text":", 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Memory Management and Allocation"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://juejin.im/post/6844903795739082760#heading-7","title":""},"content":[{"type":"text","text":"圖解Go語言內存分配"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://draveness.me/golang/docs/part3-runtime/ch07-memory/golang-memory-allocator/","title":""},"content":[{"type":"text","text":"內存分配器"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"感謝你閱讀我的文章，微信搜索公衆號「網管叨bi叨」第一時間獲取更多原創圖解Go語言原理的文章。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}
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