Initial stab at Venti.

src/cmd/venti/dcache.c

@@ -0,0 +1,372 @@
+#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);
+}