| 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 | ----- SHOULD WE GIVE PERFORMANCE AND USABILITY COMPARISON OF DIFFERENT INTERFACES THAT WE TRIED? ----- |
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| 36 | |
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| 37 | \PAB{Often Performance is its own chapter. I added one for now.} |
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| 38 | |
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| 39 | Performance evaluation using u-benchmark suite. |
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| 40 | |
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| 41 | \noindent |
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| 42 | ==================== |
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| 43 | |
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| 44 | \newpage |
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| 45 | \paragraph{Design 1: Decentralized} |
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| 46 | Fixed number of heaps: shard the heap into N heaps each with a bump-area allocated from the @sbrk@ area. |
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| 47 | Kernel threads (KT) are assigned to the N heaps. |
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| 48 | When KTs $\le$ N, the heaps are uncontented. |
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| 49 | When KTs $>$ N, the heaps are contented. |
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| 50 | By adjusting N, this approach reduces storage at the cost of speed due to contention. |
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| 51 | In all cases, a thread acquires/releases a lock, contented or uncontented. |
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| 52 | \begin{cquote} |
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| 53 | \centering |
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| 54 | \input{AllocDS1} |
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| 55 | \end{cquote} |
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| 56 | 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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| 57 | On KT deletion, its heap freed-storage needs to be distributed somewhere. |
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| 58 | |
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| 59 | \paragraph{Design 2: Centralized} |
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| 60 | |
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| 61 | One heap, but lower bucket sizes are N-shared across KTs. |
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| 62 | 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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| 63 | When KTs $\le$ N, the important bucket sizes are uncontented. |
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| 64 | When KTs $>$ N, the free buckets are contented. |
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| 65 | Therefore, threads are only contending for a small number of buckets, which are distributed among them to reduce contention. |
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| 66 | \begin{cquote} |
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| 67 | \centering |
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| 68 | \input{AllocDS2} |
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| 69 | \end{cquote} |
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| 70 | 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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| 71 | When no thread is assigned a bucket number, its free storage is unavailable. |
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| 72 | 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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