src/cmd/venti/dcache.c - plan9 - Git at Google

 #include "stdinc.h"
 #include "dat.h"
 #include "fns.h"

 typedef struct DCache	DCache;

 enum
 {
 	HashLog		= 9,
 	HashSize	= 1<<HashLog,
 	HashMask	= HashSize - 1,
 };

 struct DCache
 {
 	QLock		lock;
 	Rendez		full;
 	DBlock		*free;			/* list of available lumps */
 	u32int		now;			/* ticks for usage timestamps */
 	int		size;			/* max. size of any block; allocated to each block */
 	DBlock		**heads;		/* hash table for finding address */
 	int		nheap;			/* number of available victims */
 	DBlock		**heap;			/* heap for locating victims */
 	int		nblocks;		/* number of blocks allocated */
 	DBlock		*blocks;		/* array of block descriptors */
 	u8int		*mem;			/* memory for all block descriptors */
 };

 static DCache	dcache;

 static int	downheap(int i, DBlock *b);
 static int	upheap(int i, DBlock *b);
 static DBlock	*bumpdblock(void);
 static void	delheap(DBlock *db);
 static void	fixheap(int i, DBlock *b);

 void
 initdcache(u32int mem)
 {
 	DBlock *b, *last;
 	u32int nblocks, blocksize;
 	int i;

 	if(mem < maxblocksize * 2)
 		sysfatal("need at least %d bytes for the disk cache", maxblocksize * 2);
 	if(maxblocksize == 0)
 		sysfatal("no max. block size given for disk cache");
 	blocksize = maxblocksize;
 	nblocks = mem / blocksize;
 	if(0)
 		fprint(2, "initialize disk cache with %d blocks of %d bytes\n", nblocks, blocksize);
 	dcache.full.l = &dcache.lock;
 	dcache.nblocks = nblocks;
 	dcache.size = blocksize;
 	dcache.heads = MKNZ(DBlock*, HashSize);
 	dcache.heap = MKNZ(DBlock*, nblocks);
 	dcache.blocks = MKNZ(DBlock, nblocks);
 	dcache.mem = MKNZ(u8int, nblocks * blocksize);

 	last = nil;
 	for(i = 0; i < nblocks; i++){
 		b = &dcache.blocks[i];
 		b->data = &dcache.mem[i * blocksize];
 		b->heap = TWID32;
 		b->next = last;
 		last = b;
 	}
 	dcache.free = last;
 	dcache.nheap = 0;
 }

 static u32int
 pbhash(u64int addr)
 {
 	u32int h;

 #define hashit(c)	((((c) * 0x6b43a9b5) >> (32 - HashLog)) & HashMask)
 	h = (addr >> 32) ^ addr;
 	return hashit(h);
 }

 DBlock*
 getdblock(Part *part, u64int addr, int read)
 {
 	DBlock *b;
 	u32int h, size;

 	size = part->blocksize;
 	if(size > dcache.size){
 		seterr(EAdmin, "block size %d too big for cache", size);
 		return nil;
 	}
 	h = pbhash(addr);

 	/*
 	 * look for the block in the cache
 	 */
 //checkdcache();
 	qlock(&dcache.lock);
 again:
 	for(b = dcache.heads[h]; b != nil; b = b->next){
 		if(b->part == part && b->addr == addr){
 			qlock(&stats.lock);
 			stats.pchit++;
 			qunlock(&stats.lock);
 			goto found;
 		}
 	}
 	qlock(&stats.lock);
 	stats.pcmiss++;
 	qunlock(&stats.lock);

 	/*
 	 * missed: locate the block with the oldest second to last use.
 	 * remove it from the heap, and fix up the heap.
 	 */
 	b = bumpdblock();
 	if(b == nil){
 		logerr(EAdmin, "all disk cache blocks in use");
 		rsleep(&dcache.full);
 		goto again;
 	}

 	/*
 	 * the new block has no last use, so assume it happens sometime in the middle
 ZZZ this is not reasonable
 	 */
 	b->used = (b->used2 + dcache.now) / 2;

 	/*
 	 * rechain the block on the correct hash chain
 	 */
 	b->next = dcache.heads[h];
 	dcache.heads[h] = b;
 	if(b->next != nil)
 		b->next->prev = b;
 	b->prev = nil;

 	b->addr = addr;
 	b->part = part;
 	b->size = 0;

 found:
 	b->ref++;
 	b->used2 = b->used;
 	b->used = dcache.now++;
 	if(b->heap != TWID32)
 		fixheap(b->heap, b);

 	qunlock(&dcache.lock);
 //checkdcache();

 	qlock(&b->lock);
 	if(b->size != size){
 		if(b->size < size){
 			if(!read)
 				memset(&b->data[b->size], 0, size - b->size);
 			else{
 				if(readpart(part, addr + b->size, &b->data[b->size], size - b->size) < 0){
 					putdblock(b);
 					return nil;
 				}
 				qlock(&stats.lock);
 				stats.pcreads++;
 				stats.pcbreads += size - b->size;
 				qunlock(&stats.lock);
 			}
 		}
 		b->size = size;
 	}

 	return b;
 }

 void
 putdblock(DBlock *b)
 {
 	if(b == nil)
 		return;

 	qunlock(&b->lock);
 //checkdcache();
 	qlock(&dcache.lock);
 	if(--b->ref == 0){
 		if(b->heap == TWID32)
 			upheap(dcache.nheap++, b);
 		rwakeup(&dcache.full);
 	}

 	qunlock(&dcache.lock);
 //checkdcache();
 }

 /*
  * remove some block from use and update the free list and counters
  */
 static DBlock*
 bumpdblock(void)
 {
 	DBlock *b;
 	ulong h;

 	b = dcache.free;
 	if(b != nil){
 		dcache.free = b->next;
 		return b;
 	}

 	/*
 	 * remove blocks until we find one that is unused
 	 * referenced blocks are left in the heap even though
 	 * they can't be scavenged; this is simple a speed optimization
 	 */
 	for(;;){
 		if(dcache.nheap == 0)
 			return nil;
 		b = dcache.heap[0];
 		delheap(b);
 		if(!b->ref)
 			break;
 	}

 	/*
 	 * unchain the block
 	 */
 	if(b->prev == nil){
 		h = pbhash(b->addr);
 		if(dcache.heads[h] != b)
 			sysfatal("bad hash chains in disk cache");
 		dcache.heads[h] = b->next;
 	}else
 		b->prev->next = b->next;
 	if(b->next != nil)
 		b->next->prev = b->prev;

 	return b;
 }

 /*
  * delete an arbitrary block from the heap
  */
 static void
 delheap(DBlock *db)
 {
 	fixheap(db->heap, dcache.heap[--dcache.nheap]);
 	db->heap = TWID32;
 }

 /*
  * push an element up or down to it's correct new location
  */
 static void
 fixheap(int i, DBlock *b)
 {
 	if(upheap(i, b) == i)
 		downheap(i, b);
 }

 static int
 upheap(int i, DBlock *b)
 {
 	DBlock *bb;
 	u32int now;
 	int p;

 	now = dcache.now;
 	for(; i != 0; i = p){
 		p = (i - 1) >> 1;
 		bb = dcache.heap[p];
 		if(b->used2 - now >= bb->used2 - now)
 			break;
 		dcache.heap[i] = bb;
 		bb->heap = i;
 	}

 	dcache.heap[i] = b;
 	b->heap = i;
 	return i;
 }

 static int
 downheap(int i, DBlock *b)
 {
 	DBlock *bb;
 	u32int now;
 	int k;

 	now = dcache.now;
 	for(; ; i = k){
 		k = (i << 1) + 1;
 		if(k >= dcache.nheap)
 			break;
 		if(k + 1 < dcache.nheap && dcache.heap[k]->used2 - now > dcache.heap[k + 1]->used2 - now)
 			k++;
 		bb = dcache.heap[k];
 		if(b->used2 - now <= bb->used2 - now)
 			break;
 		dcache.heap[i] = bb;
 		bb->heap = i;
 	}

 	dcache.heap[i] = b;
 	b->heap = i;
 	return i;
 }

 static void
 findblock(DBlock *bb)
 {
 	DBlock *b, *last;
 	int h;

 	last = nil;
 	h = pbhash(bb->addr);
 	for(b = dcache.heads[h]; b != nil; b = b->next){
 		if(last != b->prev)
 			sysfatal("bad prev link");
 		if(b == bb)
 			return;
 		last = b;
 	}
 	sysfatal("block missing from hash table");
 }

 void
 checkdcache(void)
 {
 	DBlock *b;
 	u32int size, now;
 	int i, k, refed, nfree;

 	qlock(&dcache.lock);
 	size = dcache.size;
 	now = dcache.now;
 	for(i = 0; i < dcache.nheap; i++){
 		if(dcache.heap[i]->heap != i)
 			sysfatal("dc: mis-heaped at %d: %d", i, dcache.heap[i]->heap);
 		if(i > 0 && dcache.heap[(i - 1) >> 1]->used2 - now > dcache.heap[i]->used2 - now)
 			sysfatal("dc: bad heap ordering");
 		k = (i << 1) + 1;
 		if(k < dcache.nheap && dcache.heap[i]->used2 - now > dcache.heap[k]->used2 - now)
 			sysfatal("dc: bad heap ordering");
 		k++;
 		if(k < dcache.nheap && dcache.heap[i]->used2 - now > dcache.heap[k]->used2 - now)
 			sysfatal("dc: bad heap ordering");
 	}

 	refed = 0;
 	for(i = 0; i < dcache.nblocks; i++){
 		b = &dcache.blocks[i];
 		if(b->data != &dcache.mem[i * size])
 			sysfatal("dc: mis-blocked at %d", i);
 		if(b->ref && b->heap == TWID32)
 			refed++;
 		if(b->addr)
 			findblock(b);
 		if(b->heap != TWID32
 		&& dcache.heap[b->heap] != b)
 			sysfatal("dc: spurious heap value");
 	}

 	nfree = 0;
 	for(b = dcache.free; b != nil; b = b->next){
 		if(b->addr != 0 || b->heap != TWID32)
 			sysfatal("dc: bad free list");
 		nfree++;
 	}

 	if(dcache.nheap + nfree + refed != dcache.nblocks)
 		sysfatal("dc: missing blocks: %d %d %d", dcache.nheap, refed, dcache.nblocks);
 	qunlock(&dcache.lock);
 }
	#include "stdinc.h"
	#include "dat.h"
	#include "fns.h"

	typedef struct DCache DCache;

	enum
	{
	HashLog = 9,
	HashSize = 1<<HashLog,
	HashMask = HashSize - 1,
	};

	struct DCache
	{
	QLock lock;
	Rendez full;
	DBlock free; / list of available lumps */
	u32int now; /* ticks for usage timestamps */
	int size; /* max. size of any block; allocated to each block */
	DBlock *heads; / hash table for finding address */
	int nheap; /* number of available victims */
	DBlock *heap; / heap for locating victims */
	int nblocks; /* number of blocks allocated */
	DBlock blocks; / array of block descriptors */
	u8int mem; / memory for all block descriptors */
	};

	static DCache dcache;

	static int downheap(int i, DBlock *b);
	static int upheap(int i, DBlock *b);
	static DBlock *bumpdblock(void);
	static void delheap(DBlock *db);
	static void fixheap(int i, DBlock *b);

	void
	initdcache(u32int mem)
	{
	DBlock b, last;
	u32int nblocks, blocksize;
	int i;

	if(mem < maxblocksize * 2)
	sysfatal("need at least %d bytes for the disk cache", maxblocksize * 2);
	if(maxblocksize == 0)
	sysfatal("no max. block size given for disk cache");
	blocksize = maxblocksize;
	nblocks = mem / blocksize;
	if(0)
	fprint(2, "initialize disk cache with %d blocks of %d bytes\n", nblocks, blocksize);
	dcache.full.l = &dcache.lock;
	dcache.nblocks = nblocks;
	dcache.size = blocksize;
	dcache.heads = MKNZ(DBlock*, HashSize);
	dcache.heap = MKNZ(DBlock*, nblocks);
	dcache.blocks = MKNZ(DBlock, nblocks);
	dcache.mem = MKNZ(u8int, nblocks * blocksize);

	last = nil;
	for(i = 0; i < nblocks; i++){
	b = &dcache.blocks[i];
	b->data = &dcache.mem[i * blocksize];
	b->heap = TWID32;
	b->next = last;
	last = b;
	}
	dcache.free = last;
	dcache.nheap = 0;
	}

	static u32int
	pbhash(u64int addr)
	{
	u32int h;

	#define hashit(c) ((((c) * 0x6b43a9b5) >> (32 - HashLog)) & HashMask)
	h = (addr >> 32) ^ addr;
	return hashit(h);
	}

	DBlock*
	getdblock(Part *part, u64int addr, int read)
	{
	DBlock *b;
	u32int h, size;

	size = part->blocksize;
	if(size > dcache.size){
	seterr(EAdmin, "block size %d too big for cache", size);
	return nil;
	}
	h = pbhash(addr);

	/*
	* look for the block in the cache
	*/
	//checkdcache();
	qlock(&dcache.lock);
	again:
	for(b = dcache.heads[h]; b != nil; b = b->next){
	if(b->part == part && b->addr == addr){
	qlock(&stats.lock);
	stats.pchit++;
	qunlock(&stats.lock);
	goto found;
	}
	}
	qlock(&stats.lock);
	stats.pcmiss++;
	qunlock(&stats.lock);

	/*
	* missed: locate the block with the oldest second to last use.
	* remove it from the heap, and fix up the heap.
	*/
	b = bumpdblock();
	if(b == nil){
	logerr(EAdmin, "all disk cache blocks in use");
	rsleep(&dcache.full);
	goto again;
	}

	/*
	* the new block has no last use, so assume it happens sometime in the middle
	ZZZ this is not reasonable
	*/
	b->used = (b->used2 + dcache.now) / 2;

	/*
	* rechain the block on the correct hash chain
	*/
	b->next = dcache.heads[h];
	dcache.heads[h] = b;
	if(b->next != nil)
	b->next->prev = b;
	b->prev = nil;

	b->addr = addr;
	b->part = part;
	b->size = 0;

	found:
	b->ref++;
	b->used2 = b->used;
	b->used = dcache.now++;
	if(b->heap != TWID32)
	fixheap(b->heap, b);

	qunlock(&dcache.lock);
	//checkdcache();

	qlock(&b->lock);
	if(b->size != size){
	if(b->size < size){
	if(!read)
	memset(&b->data[b->size], 0, size - b->size);
	else{
	if(readpart(part, addr + b->size, &b->data[b->size], size - b->size) < 0){
	putdblock(b);
	return nil;
	}
	qlock(&stats.lock);
	stats.pcreads++;
	stats.pcbreads += size - b->size;
	qunlock(&stats.lock);
	}
	}
	b->size = size;
	}

	return b;
	}

	void
	putdblock(DBlock *b)
	{
	if(b == nil)
	return;

	qunlock(&b->lock);
	//checkdcache();
	qlock(&dcache.lock);
	if(--b->ref == 0){
	if(b->heap == TWID32)
	upheap(dcache.nheap++, b);
	rwakeup(&dcache.full);
	}

	qunlock(&dcache.lock);
	//checkdcache();
	}

	/*
	* remove some block from use and update the free list and counters
	*/
	static DBlock*
	bumpdblock(void)
	{
	DBlock *b;
	ulong h;

	b = dcache.free;
	if(b != nil){
	dcache.free = b->next;
	return b;
	}

	/*
	* remove blocks until we find one that is unused
	* referenced blocks are left in the heap even though
	* they can't be scavenged; this is simple a speed optimization
	*/
	for(;;){
	if(dcache.nheap == 0)
	return nil;
	b = dcache.heap[0];
	delheap(b);
	if(!b->ref)
	break;
	}

	/*
	* unchain the block
	*/
	if(b->prev == nil){
	h = pbhash(b->addr);
	if(dcache.heads[h] != b)
	sysfatal("bad hash chains in disk cache");
	dcache.heads[h] = b->next;
	}else
	b->prev->next = b->next;
	if(b->next != nil)
	b->next->prev = b->prev;

	return b;
	}

	/*
	* delete an arbitrary block from the heap
	*/
	static void
	delheap(DBlock *db)
	{
	fixheap(db->heap, dcache.heap[--dcache.nheap]);
	db->heap = TWID32;
	}

	/*
	* push an element up or down to it's correct new location
	*/
	static void
	fixheap(int i, DBlock *b)
	{
	if(upheap(i, b) == i)
	downheap(i, b);
	}

	static int
	upheap(int i, DBlock *b)
	{
	DBlock *bb;
	u32int now;
	int p;

	now = dcache.now;
	for(; i != 0; i = p){
	p = (i - 1) >> 1;
	bb = dcache.heap[p];
	if(b->used2 - now >= bb->used2 - now)
	break;
	dcache.heap[i] = bb;
	bb->heap = i;
	}

	dcache.heap[i] = b;
	b->heap = i;
	return i;
	}

	static int
	downheap(int i, DBlock *b)
	{
	DBlock *bb;
	u32int now;
	int k;

	now = dcache.now;
	for(; ; i = k){
	k = (i << 1) + 1;
	if(k >= dcache.nheap)
	break;
	if(k + 1 < dcache.nheap && dcache.heap[k]->used2 - now > dcache.heap[k + 1]->used2 - now)
	k++;
	bb = dcache.heap[k];
	if(b->used2 - now <= bb->used2 - now)
	break;
	dcache.heap[i] = bb;
	bb->heap = i;
	}

	dcache.heap[i] = b;
	b->heap = i;
	return i;
	}

	static void
	findblock(DBlock *bb)
	{
	DBlock b, last;
	int h;

	last = nil;
	h = pbhash(bb->addr);
	for(b = dcache.heads[h]; b != nil; b = b->next){
	if(last != b->prev)
	sysfatal("bad prev link");
	if(b == bb)
	return;
	last = b;
	}
	sysfatal("block missing from hash table");
	}

	void
	checkdcache(void)
	{
	DBlock *b;
	u32int size, now;
	int i, k, refed, nfree;

	qlock(&dcache.lock);
	size = dcache.size;
	now = dcache.now;
	for(i = 0; i < dcache.nheap; i++){
	if(dcache.heap[i]->heap != i)
	sysfatal("dc: mis-heaped at %d: %d", i, dcache.heap[i]->heap);
	if(i > 0 && dcache.heap[(i - 1) >> 1]->used2 - now > dcache.heap[i]->used2 - now)
	sysfatal("dc: bad heap ordering");
	k = (i << 1) + 1;
	if(k < dcache.nheap && dcache.heap[i]->used2 - now > dcache.heap[k]->used2 - now)
	sysfatal("dc: bad heap ordering");
	k++;
	if(k < dcache.nheap && dcache.heap[i]->used2 - now > dcache.heap[k]->used2 - now)
	sysfatal("dc: bad heap ordering");
	}

	refed = 0;
	for(i = 0; i < dcache.nblocks; i++){
	b = &dcache.blocks[i];
	if(b->data != &dcache.mem[i * size])
	sysfatal("dc: mis-blocked at %d", i);
	if(b->ref && b->heap == TWID32)
	refed++;
	if(b->addr)
	findblock(b);
	if(b->heap != TWID32
	&& dcache.heap[b->heap] != b)
	sysfatal("dc: spurious heap value");
	}

	nfree = 0;
	for(b = dcache.free; b != nil; b = b->next){
	if(b->addr != 0 \|\| b->heap != TWID32)
	sysfatal("dc: bad free list");
	nfree++;
	}

	if(dcache.nheap + nfree + refed != dcache.nblocks)
	sysfatal("dc: missing blocks: %d %d %d", dcache.nheap, refed, dcache.nblocks);
	qunlock(&dcache.lock);
	}