External Fragmentation

External Fragmentation - External Fragmentation External...

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External Fragmentation External Fragmentation is the waste of memory in the free list due to small non- contiguous blocks that cannot satisfy a large request. 64 16 40 0x110 0x4000 0x8000 p = malloc(100); 100 bytes object + 8 bytes header = 108 bytes total The allocation cannot be satisfied even though the free list has more than 108 bytes. The allocator will need to get more memory from the OS.
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External Fragmentation The external fragmentation can be measured as: Ext. Fragmentation%=100*(1- size_largest_block/total_mem_in_free_list) 64 16 40 0x110 0x4000 0x8000 Ext. Fragmentation%=100(1-64/120)=47% If there is only one block in the list ext fragmentation=0%
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Segregated Free Lists It is another data structure for memory allocation. There are multiple free lists for different sizes. Size 8 16 32 6 4 128 256 >=512
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Segregated Free Lists Very often the fixed sizes are powers of two.
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This note was uploaded on 01/30/2012 for the course CS 354 taught by Professor Staff during the Fall '08 term at Purdue.

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External Fragmentation - External Fragmentation External...

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