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kmemcheckkmemcheckPosted Nov 29, 2007 13:19 UTC (Thu) by dw (subscriber, #12017)Parent article: kmemcheck
Doubling the size of every allocation seems pretty wasteful, couldn't a bitmap be used instead, with byte or even word-level granularity? new_size = (size + (size/8))
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kmemcheck Posted Nov 29, 2007 14:44 UTC (Thu) by nix (subscriber, #2304) [Link] A bitmap definitely can be used instead. (This is how valgrind's memcheck tool implements uninitialized checks, although using JIT simulation rather than page faulting to detect accesses.)
kmemcheck Posted Nov 29, 2007 15:20 UTC (Thu) by jreiser (subscriber, #11027) [Link] On a 32-bit machine it is tempting to use 8 bits (an entire byte) to track access to 32 bits (one word) of memory. This gives speed while still saving some space.
kmemcheck Posted Nov 29, 2007 18:16 UTC (Thu) by felixfix (subscriber, #242) [Link] The code to map bits would be slower; maybe he did not like the tradeoff.
kmemcheck Posted Nov 29, 2007 18:41 UTC (Thu) by lysse (guest, #3190) [Link] When there's already a page fault happening on every memory access, I have some doubts of the significance of such additional overhead.
kmemcheck Posted Nov 29, 2007 18:52 UTC (Thu) by felixfix (subscriber, #242) [Link] Well, hmmmm, I guess I was thinking just enough to stick my foot in my mouth :-)
kmemcheck Posted Nov 29, 2007 19:06 UTC (Thu) by nix (subscriber, #2304) [Link] Also the extra memory accesses will tend to blow the cache more if you use more memory to track the uninit state.
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