| 1 | \chapter{Allocator}
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| 2 |
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| 3 | \noindent
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| 4 | ====================
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| 5 |
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| 6 | Writing Points:
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| 7 | \begin{itemize}
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| 8 | \item
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| 9 | Objective of uHeapLmmm.
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| 10 | \item
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| 11 | Design philosophy.
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| 12 | \item
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| 13 | Background and previous design of uHeapLmmm.
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| 14 | \item
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| 15 | Distributed design of uHeapLmmm.
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| 16 |
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| 17 | ----- SHOULD WE GIVE IMPLEMENTATION DETAILS HERE? -----
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| 18 |
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| 19 | \PAB{Maybe. There might be an Implementation chapter.}
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| 20 | \item
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| 21 | figure.
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| 22 | \item
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| 23 | Advantages of distributed design.
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| 24 | \end{itemize}
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| 25 |
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| 26 | The new features added to uHeapLmmm (incl. @malloc_size@ routine)
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| 27 | \CFA alloc interface with examples.
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| 28 | \begin{itemize}
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| 29 | \item
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| 30 | Why did we need it?
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| 31 | \item
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| 32 | The added benefits.
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| 33 | \end{itemize}
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| 34 |
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| 35 |
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| 36 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 37 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 38 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% uHeapLmmm Design
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| 39 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 40 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 41 |
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| 42 | \section{Objective of uHeapLmmm}
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| 43 | UHeapLmmm is a lightweight memory allocator. The objective behind uHeapLmmm is to design a minimal concurrent memory allocator that has new features and also fulfills GNU C Library requirements (FIX ME: cite requirements).
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| 44 |
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| 45 | \subsection{Design philosophy}
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| 46 |
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| 47 |
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| 48 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 49 |
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| 50 | \section{Background and previous design of uHeapLmmm}
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| 51 |
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| 52 |
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| 53 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 54 |
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| 55 | \section{Distributed design of uHeapLmmm}
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| 56 |
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| 57 |
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| 58 | \subsection{Advantages of distributed design}
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| 59 |
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| 60 |
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| 61 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 62 |
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| 63 | \section{Added Features}
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| 64 |
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| 65 |
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| 66 | \subsection{Methods}
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| 67 | Why did we need it?
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| 68 | The added benefits.
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| 69 |
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| 70 |
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| 71 | \subsection{Alloc Interface}
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| 72 | Why did we need it?
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| 73 | The added benefits.
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| 74 |
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| 75 |
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| 76 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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| 77 | % Following is added by Peter
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| 78 |
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| 79 | \noindent
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| 80 | ====================
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| 81 |
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| 82 | \newpage
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| 83 | \paragraph{Design 1: Decentralized}
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| 84 | Fixed number of heaps: shard the heap into N heaps each with a bump-area allocated from the @sbrk@ area.
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| 85 | Kernel threads (KT) are assigned to the N heaps.
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| 86 | When KTs $\le$ N, the heaps are uncontented.
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| 87 | When KTs $>$ N, the heaps are contented.
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| 88 | By adjusting N, this approach reduces storage at the cost of speed due to contention.
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| 89 | In all cases, a thread acquires/releases a lock, contented or uncontented.
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| 90 | \begin{cquote}
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| 91 | \centering
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| 92 | \input{AllocDS1}
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| 93 | \end{cquote}
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| 94 | Problems: need to know when a KT is created and destroyed to know when to create/delete the KT's heap.
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| 95 | On KT deletion, its heap freed-storage needs to be distributed somewhere.
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| 96 |
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| 97 | \paragraph{Design 2: Centralized}
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| 98 |
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| 99 | One heap, but lower bucket sizes are N-shared across KTs.
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| 100 | This design leverages the fact that 95\% of allocation requests are less than 512 bytes and there are only 3--5 different request sizes.
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| 101 | When KTs $\le$ N, the important bucket sizes are uncontented.
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| 102 | When KTs $>$ N, the free buckets are contented.
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| 103 | Therefore, threads are only contending for a small number of buckets, which are distributed among them to reduce contention.
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| 104 | \begin{cquote}
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| 105 | \centering
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| 106 | \input{AllocDS2}
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| 107 | \end{cquote}
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| 108 | Problems: need to know when a kernel thread (KT) is created and destroyed to know when to assign a shared bucket-number.
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| 109 | When no thread is assigned a bucket number, its free storage is unavailable.
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| 110 | It is possible to use sharing and stealing techniques to share/find unused storage, when a free list is unused or empty.
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