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/* |
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======================================================================= |
| 3 |
Cache for out-of-core octree. |
| 4 |
|
| 5 |
Uses an LRU page replacement scheme. Page table nodes are stored in |
| 6 |
order of reference in a doubly linked list, with the most recently used |
| 7 |
(MRU) page at the head, and the least recently used (LRU) at the tail. |
| 8 |
|
| 9 |
Nodes are referenced by the page's base address via a hashtable for |
| 10 |
constant time access (in the absence of hash collisions). Hash |
| 11 |
collisions can be limited by adjusting the hashtable load factor |
| 12 |
OOC_CACHE_LOAD; this is the fraction of the number of pages that will |
| 13 |
actually be cached. |
| 14 |
|
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Roland Schregle (roland.schregle@{hslu.ch, gmail.com}) |
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(c) Lucerne University of Applied Sciences and Arts, |
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supported by the Swiss National Science Foundation (SNSF, #147053) |
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======================================================================= |
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|
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$Id: ooccache.c,v 1.12 2015/11/16 13:33:13 taschreg Exp taschreg $ |
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*/ |
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|
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|
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#include <stdlib.h> |
| 25 |
#include <unistd.h> |
| 26 |
#include "ooccache.h" |
| 27 |
|
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|
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|
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static OOC_CacheIdx OOC_PrevPrime (OOC_CacheIdx n) |
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/* Return largest prime number <= n */ |
| 32 |
{ |
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OOC_CacheIdx n2 = n + 1, i; |
| 34 |
|
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do { |
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n2--; |
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for (i = 2; n2 % i && i <= n2 >> 1; i++); |
| 38 |
} while (!(n2 % i)); |
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|
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return n2; |
| 41 |
} |
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|
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|
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|
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int OOC_CacheInit (OOC_Cache *cache, unsigned numPages, |
| 46 |
unsigned recPerPage, unsigned recSize) |
| 47 |
{ |
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OOC_CacheIdx i; |
| 49 |
|
| 50 |
if (!cache) |
| 51 |
return -1; |
| 52 |
|
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/* Clamp number of pages if necessary */ |
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if (numPages < OOC_CACHE_MINPAGES) { |
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numPages = OOC_CACHE_MINPAGES; |
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fputs("OOC_CacheInit: clamping num pages to min\n", stderr); |
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} |
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|
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if (numPages >= OOC_CACHEIDX_NULL) { |
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numPages = OOC_CACHEIDX_NULL - 1; |
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fputs("OOC_CacheInit: clamping num pages to max\n", stderr); |
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} |
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|
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/* Round numPages to next prime to reduce hash clustering & collisions */ |
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numPages = OOC_PrevPrime(numPages); |
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|
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cache -> recPerPage = recPerPage; |
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cache -> numPages = numPages; |
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cache -> recSize = recSize; |
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cache -> pageSize = (unsigned long)cache -> recPerPage * |
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cache -> recSize; |
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cache -> pageCnt = 0; |
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cache -> numHits = cache -> numReads = cache -> numColl = |
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cache -> numRept = 0; |
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cache -> mru = cache -> lru = OOC_CACHEIDX_NULL; |
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cache -> lastKey = 0; |
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cache -> lastPage = NULL; |
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|
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/* Allocate & init hashtable */ |
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if (!(cache -> pageTable = calloc(numPages, sizeof(OOC_CacheNode)))) { |
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perror("OOC_InitCache: failed pagetable allocation"); |
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return -1; |
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} |
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|
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for (i = 0; i < numPages; i++) { |
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cache -> pageTable [i].data = NULL; |
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cache -> pageTable [i].key = 0; |
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cache -> pageTable [i].prev = cache -> pageTable [i].next = |
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OOC_CACHEIDX_NULL; |
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} |
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|
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#ifdef OOC_CACHE_STATS |
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fprintf(stderr, |
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"OOC_InitCache: caching %d pages @ %d records (%.2f Mb)\n", |
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cache -> numPages, cache -> recPerPage, |
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(float)cache -> numPages * cache -> pageSize / (1L << 20)); |
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#endif |
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|
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return 0; |
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} |
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|
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|
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|
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static OOC_CacheIdx OOC_CacheFind (OOC_Cache *cache, OOC_CacheKey key) |
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/* Return index to pagetable node for given key; collisions are resolved |
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* via the probe sequence defined by OOC_CACHE_NEXT() */ |
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{ |
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OOC_CacheIdx idx = OOC_CACHE_HASH(key, cache -> numPages); |
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OOC_CacheNode *page = cache -> pageTable + idx; |
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|
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/* Find matching pagetable node starting from idx and stop at the first |
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* empty node; a full table would result in an infinite loop! */ |
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while (page -> data && page -> key != key) { |
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idx = OOC_CACHE_NEXT(idx, cache -> numPages); |
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page = cache -> pageTable + idx; |
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cache -> numColl++; |
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} |
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|
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return idx; |
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} |
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|
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|
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|
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static void OOC_CacheUnlink (OOC_Cache *cache, OOC_CacheIdx pageIdx) |
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/* Unlink page from history chain, updating LRU in cache if necessary */ |
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{ |
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OOC_CacheNode *page = cache -> pageTable + pageIdx; |
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|
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/* Unlink prev/next index */ |
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if (page -> prev != OOC_CACHEIDX_NULL) |
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cache -> pageTable [page -> prev].next = page -> next; |
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|
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if (page -> next != OOC_CACHEIDX_NULL) |
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cache -> pageTable [page -> next].prev = page -> prev; |
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|
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/* Update LRU index */ |
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if (pageIdx == cache -> lru) |
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cache -> lru = page -> prev; |
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} |
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|
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|
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|
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static void OOC_CacheRelink (OOC_Cache *cache, OOC_CacheIdx pageIdx) |
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/* Update history chain with new page index */ |
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{ |
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OOC_CacheNode *page = cache -> pageTable + pageIdx; |
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|
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if (page -> prev != OOC_CACHEIDX_NULL) |
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cache -> pageTable [page -> prev].next = pageIdx; |
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|
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if (page -> next != OOC_CACHEIDX_NULL) |
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cache -> pageTable [page -> next].prev = pageIdx; |
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} |
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|
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|
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|
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static void OOC_CacheSetMRU (OOC_Cache *cache, OOC_CacheIdx pageIdx) |
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/* Set page as most recently used and move to head of history chain */ |
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{ |
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OOC_CacheNode *page = cache -> pageTable + pageIdx; |
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|
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OOC_CacheUnlink(cache, pageIdx); |
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page -> prev = OOC_CACHEIDX_NULL; |
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page -> next = cache -> mru; |
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cache -> pageTable [cache -> mru].prev = pageIdx; |
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cache -> mru = pageIdx; |
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} |
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|
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|
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|
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static void *OOC_CacheDelete (OOC_Cache *cache, OOC_CacheIdx pageIdx) |
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/* Delete cache node at pageIdx and tidy up fragmentation in pagetable to |
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* minimise collisions. Returns pointer to deleted node's page data |
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* |
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* !!! Note cache -> pageCnt is NOT decremented as this is immediately |
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* !!! followed by a call to OOC_CacheNew() in OOC_CacheData() */ |
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{ |
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OOC_CacheNode *page = cache -> pageTable + pageIdx, *nextPage; |
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OOC_CacheIdx nextIdx; |
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void *delData = page -> data, *nextData; |
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|
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/* Unlink page from history chain */ |
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OOC_CacheUnlink(cache, pageIdx); |
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|
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/* Free pagetable node */ |
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page -> data = NULL; |
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|
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nextIdx = OOC_CACHE_NEXT(pageIdx, cache -> numPages); |
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nextPage = cache -> pageTable + nextIdx; |
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|
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/* Close gaps in probe sequence until empty node found */ |
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while ((nextData = nextPage -> data)) { |
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/* Mark next node as free and reprobe for its key */ |
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nextPage -> data = NULL; |
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pageIdx = OOC_CacheFind(cache, nextPage -> key); |
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page = cache -> pageTable + pageIdx; |
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|
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/* Set page data pointer & reactivate page */ |
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page -> data = nextData; |
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|
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if (pageIdx != nextIdx) { |
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/* Next page maps to freed node; relocate to close gap and update |
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* history chain and LRU/MRU if necessary */ |
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page -> key = nextPage -> key; /* memcpy() faster ? */ |
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page -> prev = nextPage -> prev; |
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page -> next = nextPage -> next; |
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OOC_CacheRelink(cache, pageIdx); |
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|
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if (cache -> lru == nextIdx) |
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cache -> lru = pageIdx; |
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|
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if (cache -> mru == nextIdx) |
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cache -> mru = pageIdx; |
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} |
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|
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nextIdx = OOC_CACHE_NEXT(nextIdx, cache -> numPages); |
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nextPage = cache -> pageTable + nextIdx; |
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} |
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|
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return delData; |
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} |
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|
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|
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|
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static OOC_CacheNode *OOC_CacheNew (OOC_Cache *cache, OOC_CacheIdx pageIdx, |
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OOC_CacheKey pageKey, void *pageData) |
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/* Init new pagetable node with given index, key and data. Returns pointer |
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* to new node */ |
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{ |
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OOC_CacheNode *page = cache -> pageTable + pageIdx; |
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|
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page -> prev = page -> next = OOC_CACHEIDX_NULL; |
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page -> key = pageKey; |
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page -> data = pageData; |
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|
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return page; |
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} |
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|
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|
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|
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#ifdef OOC_CACHE_CHECK |
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static int OOC_CacheCheck (OOC_Cache *cache) |
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/* Run sanity checks on hashtable and page list */ |
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{ |
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OOC_CacheIdx i, pageCnt = 0; |
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OOC_CacheNode *page; |
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|
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/* Check pagetable mapping */ |
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for (i = 0, page = cache->pageTable; i < cache->numPages; i++, page++) |
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if (page -> data) { |
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/* Check hash func maps page key to this node */ |
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if (OOC_CacheFind(cache, page -> key) != i) { |
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fputs("OOC_CacheCheck: hashing inconsistency\n", stderr); |
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return -1; |
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} |
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|
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pageCnt++; |
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} |
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|
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if (pageCnt != cache -> pageCnt) { |
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fputs("OOC_CacheCheck: pagetable count inconsistency\n", stderr); |
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return -1; |
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} |
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|
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if (cache -> mru == OOC_CACHEIDX_NULL || |
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cache -> lru == OOC_CACHEIDX_NULL) { |
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fputs("OOC_CacheCheck: undefined MRU/LRU\n", stderr); |
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return -1; |
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} |
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|
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pageCnt = 0; |
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i = cache -> mru; |
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|
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/* Check page history */ |
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while (i != OOC_CACHEIDX_NULL) { |
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/* Check link to previous page (should be none for MRU) */ |
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page = cache -> pageTable + i; |
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|
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if (i == cache -> mru) |
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if (page -> prev != OOC_CACHEIDX_NULL) { |
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fputs("OOC_CacheCheck: MRU inconsistency\n", stderr); |
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return -1; |
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} |
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else; |
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else if (page -> prev == OOC_CACHEIDX_NULL || |
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cache -> pageTable [page -> prev].next != i) { |
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fputs("OOC_CacheCheck: prev page inconsistency\n", stderr); |
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return -1; |
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} |
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|
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/* Check link to next page node (should be none for LRU) */ |
| 292 |
if (i == cache -> lru) |
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if (page -> next != OOC_CACHEIDX_NULL) { |
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fputs("OOC_CacheCheck: LRU inconsistency\n", stderr); |
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return -1; |
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} |
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else; |
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else if (page -> next != OOC_CACHEIDX_NULL && |
| 299 |
cache -> pageTable [page -> next].prev != i) { |
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fputs("OOC_CacheCheck: next page inconsistency\n", stderr); |
| 301 |
return -1; |
| 302 |
} |
| 303 |
|
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/* Check LRU is at tail of page history */ |
| 305 |
if (page -> next == OOC_CACHEIDX_NULL && i != cache -> lru) { |
| 306 |
fputs("OOC_CacheCheck: page history tail not LRU\n", stderr); |
| 307 |
return -1; |
| 308 |
} |
| 309 |
|
| 310 |
i = page -> next; |
| 311 |
pageCnt++; |
| 312 |
} |
| 313 |
|
| 314 |
if (pageCnt != cache -> pageCnt) { |
| 315 |
fputs("OOC_CacheCheck: page history count inconsistency\n", stderr); |
| 316 |
return -1; |
| 317 |
} |
| 318 |
|
| 319 |
return 0; |
| 320 |
} |
| 321 |
#endif |
| 322 |
|
| 323 |
|
| 324 |
|
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void *OOC_CacheData (OOC_Cache *cache, FILE *file, unsigned long recIdx) |
| 326 |
{ |
| 327 |
const OOC_CacheKey pageKey = recIdx / cache -> recPerPage; |
| 328 |
OOC_CacheNode *page = NULL; |
| 329 |
|
| 330 |
/* We assume locality of reference, and that it's likely the same page |
| 331 |
* will therefore be accessed sequentially; in this case we just reuse |
| 332 |
* the pagetable index */ |
| 333 |
if (pageKey != cache -> lastKey || !cache -> pageCnt) { |
| 334 |
OOC_CacheIdx pageIdx = OOC_CacheFind(cache, pageKey); |
| 335 |
void *pageData; |
| 336 |
|
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page = cache -> pageTable + pageIdx; |
| 338 |
|
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if (!page -> data) { |
| 340 |
/* Page not cached; insert in pagetable */ |
| 341 |
const unsigned long filePos = cache -> pageSize * pageKey; |
| 342 |
|
| 343 |
if (cache -> pageCnt < OOC_CACHE_LOAD * cache -> numPages) { |
| 344 |
/* Cache not fully loaded; allocate new page data */ |
| 345 |
if (!(pageData = calloc(cache -> recPerPage, cache -> recSize))) { |
| 346 |
perror("OOC_CacheData: failed page allocation"); |
| 347 |
return NULL; |
| 348 |
} |
| 349 |
|
| 350 |
/* Init LRU and MRU if necessary */ |
| 351 |
if (cache -> mru == OOC_CACHEIDX_NULL || |
| 352 |
cache -> lru == OOC_CACHEIDX_NULL) |
| 353 |
cache -> mru = cache -> lru = pageIdx; |
| 354 |
|
| 355 |
cache -> pageCnt++; |
| 356 |
} |
| 357 |
else { |
| 358 |
/* Cache fully loaded; adding more entries would aggravate |
| 359 |
* hash collisions, so evict LRU page. We reuse its |
| 360 |
* allocated page data and then overwrite it. */ |
| 361 |
pageData = OOC_CacheDelete(cache, cache -> lru); |
| 362 |
|
| 363 |
/* Update page index as it may have moved forward in probe |
| 364 |
* sequence after deletion */ |
| 365 |
pageIdx = OOC_CacheFind(cache, pageKey); |
| 366 |
} |
| 367 |
|
| 368 |
/* Init new pagetable node, will be linked in history below */ |
| 369 |
page = OOC_CacheNew(cache, pageIdx, pageKey, pageData); |
| 370 |
|
| 371 |
/* Load page data from file; the last page may be truncated */ |
| 372 |
if (!pread(fileno(file), page -> data, cache -> pageSize, filePos)) { |
| 373 |
fputs("OOC_CacheData: failed seek/read from data stream", stderr); |
| 374 |
return NULL; |
| 375 |
} |
| 376 |
} |
| 377 |
else |
| 378 |
/* Page in cache */ |
| 379 |
cache -> numHits++; |
| 380 |
|
| 381 |
if (cache -> mru != pageIdx) |
| 382 |
/* Cached page is now most recently used; unlink and move to front |
| 383 |
* of history chain and update MRU */ |
| 384 |
OOC_CacheSetMRU(cache, pageIdx); |
| 385 |
|
| 386 |
/* Update last page to detect repeat accesses */ |
| 387 |
cache -> lastKey = pageKey; |
| 388 |
cache -> lastPage = page; |
| 389 |
} |
| 390 |
else { |
| 391 |
/* Repeated page, skip hashing and just reuse last page */ |
| 392 |
page = cache -> lastPage; |
| 393 |
cache -> numHits++; |
| 394 |
cache -> numRept++; |
| 395 |
} |
| 396 |
|
| 397 |
cache -> numReads++; |
| 398 |
|
| 399 |
#ifdef OOC_CACHE_CHECK |
| 400 |
if (OOC_CacheCheck(cache)) |
| 401 |
return NULL; |
| 402 |
#endif |
| 403 |
|
| 404 |
/* Return pointer to record within cached page */ |
| 405 |
return page -> data + (recIdx % cache -> recPerPage) * cache -> recSize; |
| 406 |
} |
| 407 |
|
| 408 |
|
| 409 |
|
| 410 |
void OOC_DeleteCache (OOC_Cache *cache) |
| 411 |
{ |
| 412 |
OOC_CacheIdx i; |
| 413 |
|
| 414 |
for (i = 0; i < cache -> numPages; i++) |
| 415 |
if (cache -> pageTable [i].data) |
| 416 |
free(cache -> pageTable [i].data); |
| 417 |
|
| 418 |
free(cache -> pageTable); |
| 419 |
cache -> pageTable = NULL; |
| 420 |
cache -> pageCnt = 0; |
| 421 |
cache -> mru = cache -> lru = OOC_CACHEIDX_NULL; |
| 422 |
} |
