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Diffstat (limited to 'documentation/euler/heap.txt')
| -rw-r--r-- | documentation/euler/heap.txt | 32 |
1 files changed, 0 insertions, 32 deletions
diff --git a/documentation/euler/heap.txt b/documentation/euler/heap.txt deleted file mode 100644 index de1deec..0000000 --- a/documentation/euler/heap.txt +++ /dev/null @@ -1,32 +0,0 @@ -this file documents dynamic memory allocation and deallocation in userspace. -the unused areas of a process's usable mapped memory are divided into "chunks" -with a start and a length, satisfying the following properties: - a) the length of a chunk is a positive power of 2 - b) the start of a chunk is a multiple of its length - c) let s be a power of 2 and k be an integer. there are never two chunks with - length s and starts s * (2 * k) and s * (2 * k + 1). if ever an operation - would result in two such chunks, they are combined into one chunk with - length 2 * s and start 2 * s * k. - -a "chunk info page" is divided into 512 64-bit integers describing up to 255 -chunks and a pointer to another chunk info page. for each n from 0 to 254: - if the (2 * n)'th integer (where the first integer is the 0th one) is 0: - the (2 * n + 1)'th integer is unused. - if the (2 * n)'th integer is not 0: - the (2 * n)'th integer describes the length of a chunk - the (2 * n + 1)'th integer describes the start of the same chunk -the 510th integer is a pointer to the next chunk info page, and the 511th -integer is never used. - -when a program calls new or malloc with needed size s, we find a free chunk of -length at least s + 8. we then remove that chunk from the list of free chunks, -and add back in whatever is left after the first s + 8 bytes, if anything. -in the first 8 bytes of the original chunk, we store the value s + 8. the -remainder of the orginal chunk is returned to the program. - -during that process, if there isn't a chunk with the needed size, one or more -new pages are requested from the kernel to create such a chunk. - -when a program calls delete or free with pointer ptr, we read the integer in -the 8 bytes starting at ptr - 8 into a variable s. we then add the region -starting at ptr - 8 with length s to the free memory. |