Date: Mon, 30 Jul 2018 15:14:14 -0400 From: Christopher Friedt <chrisfriedt@...il.com> To: musl@...ts.openwall.com Subject: Re: malloc implementation survey: omalloc On Mon, Jul 30, 2018, 11:09 AM Christopher Friedt, <chrisfriedt@...il.com> wrote: > otential for fragmentation. Otherwise though, the meta-information is > intrinsic within the pointer, which obliviates the need for external > storage. > I should clarify. The meta-info in my buddy allocator is only intrinsic if the size of ram, and offset are constant. Additionally, there is a bitmap of constant size in .data. Of course, in userspace, there would need to be 1 void*, 1 size_t, and a bitmap per PoT chunk of memory to manage. For a 4096-byte page, on a 32-bit system, that would be 4 + 4 + 256 = 304 bytes of overhead. C  The size of the bitmap (in bits) is given directly by the geometric series: F(n) = sum(k, n-1) r^k = (1-r^n)/(1-r) r is 2. If 2^U is the memory size, and 2^L is the smallest granularity of allocation, then n = U - L + 1, and the number of bits in the bitmap is F( n ). E.g. 64 bytes of memory, min 8-byte allocation, then F( 4 ) = 15 bits (2 bytes) are needed for the bitmap. Content of type "text/html" skipped
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