| 1 | \chapter{Allocator} |
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| 2 | |
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| 3 | ==================== |
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| 4 | |
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| 5 | Writing Points: |
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| 6 | |
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| 7 | Objective of uHeapLmmm. |
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| 8 | Design philosophy. |
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| 9 | Background and previous design of uHeapLmmm. |
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| 10 | |
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| 11 | Distributed design of uHeapLmmm. |
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| 12 | ----- SHOULD WE GIVE IMPLEMENTATION DETAILS HERE? ----- |
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| 13 | > figure. |
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| 14 | > Advantages of distributed design. |
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| 15 | |
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| 16 | The new features added to uHeapLmmm (incl. malloc_size routine) |
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| 17 | CFA alloc interface with examples. |
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| 18 | > Why did we need it? |
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| 19 | > The added benefits. |
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| 20 | ----- SHOULD WE GIVE PERFORMANCE AND USABILITY COMPARISON OF DIFFERENT INTERFACES THAT WE TRIED? ----- |
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| 21 | |
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| 22 | Performance evaluation using u-benchmark suite. |
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| 23 | |
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| 24 | ==================== |
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| 25 | |
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| 26 | \newpage |
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| 27 | \paragraph{Design 1: Decentralized} |
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| 28 | Fixed number of heaps: shard the heap into N heaps each with a bump-area allocated from the sbrk area. |
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| 29 | Kernel threads (KT) are assigned to the N heaps. |
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| 30 | When KTs $\le$ N, the heaps are uncontented. |
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| 31 | When KTs $>$ N, the heaps are contented. |
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| 32 | By adjusting N, this approach reduces storage at the cost of speed due to contention. |
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| 33 | In all cases, a thread acquires/releases a lock, contented or uncontented. |
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| 34 | \begin{cquote} |
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| 35 | \centering |
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| 36 | \input{AllocDS1} |
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| 37 | \end{cquote} |
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| 38 | 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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| 39 | On KT deletion, its heap freed-storage needs to be distributed somewhere. |
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| 40 | |
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| 41 | \paragraph{Design 2: Centralized} |
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| 42 | |
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| 43 | One heap, but lower bucket sizes are N-shared across KTs. |
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| 44 | 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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| 45 | When KTs $\le$ N, the important bucket sizes are uncontented. |
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| 46 | When KTs $>$ N, the free buckets are contented. |
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| 47 | Therefore, threads are only contending for a small number of buckets, which are distributed among them to reduce contention. |
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| 48 | \begin{cquote} |
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| 49 | \centering |
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| 50 | \input{AllocDS2} |
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| 51 | \end{cquote} |
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| 52 | 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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| 53 | When no thread is assigned a bucket number, its free storage is unavailable. |
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| 54 | 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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