ref: b54c61c6174251736e0a6bf30fc1631eca79210c
dir: /sys/src/libventi/cache.c/
/*
* Memory-only VtBlock cache.
*
* The cached Venti blocks are in the hash chains.
* The cached local blocks are only in the blocks array.
* The free blocks are in the heap, which is supposed to
* be indexed by second-to-last use but actually
* appears to be last use.
*/
#include <u.h>
#include <libc.h>
#include <venti.h>
int vtcachenread;
int vtcachencopy;
int vtcachenwrite;
int vttracelevel;
enum {
BioLocal = 1,
BioVenti,
BioReading,
BioWriting,
BioEmpty,
BioVentiError
};
enum {
BadHeap = ~0
};
struct VtCache
{
QLock lk;
VtConn *z;
u32int blocksize;
u32int now; /* ticks for usage time stamps */
VtBlock **hash; /* hash table for finding addresses */
int nhash;
VtBlock **heap; /* heap for finding victims */
int nheap;
VtBlock *block; /* all allocated blocks */
int nblock;
uchar *mem; /* memory for all blocks and data */
int (*write)(VtConn*, uchar[VtScoreSize], uint, uchar*, int);
};
static void cachecheck(VtCache*);
VtCache*
vtcachealloc(VtConn *z, int blocksize, ulong nblock)
{
uchar *p;
VtCache *c;
int i;
VtBlock *b;
c = vtmallocz(sizeof(VtCache));
c->z = z;
c->blocksize = (blocksize + 127) & ~127;
c->nblock = nblock;
c->nhash = nblock;
c->hash = vtmallocz(nblock*sizeof(VtBlock*));
c->heap = vtmallocz(nblock*sizeof(VtBlock*));
c->block = vtmallocz(nblock*sizeof(VtBlock));
c->mem = vtmallocz(nblock*c->blocksize);
c->write = vtwrite;
p = c->mem;
for(i=0; i<nblock; i++){
b = &c->block[i];
b->addr = NilBlock;
b->c = c;
b->data = p;
b->heap = i;
c->heap[i] = b;
p += c->blocksize;
}
c->nheap = nblock;
cachecheck(c);
return c;
}
/*
* BUG This is here so that vbackup can override it and do some
* pipelining of writes. Arguably vtwrite or vtwritepacket or the
* cache itself should be providing this functionality.
*/
void
vtcachesetwrite(VtCache *c, int (*write)(VtConn*, uchar[VtScoreSize], uint, uchar*, int))
{
if(write == nil)
write = vtwrite;
c->write = write;
}
void
vtcachefree(VtCache *c)
{
int i;
qlock(&c->lk);
cachecheck(c);
for(i=0; i<c->nblock; i++)
assert(c->block[i].ref == 0);
vtfree(c->hash);
vtfree(c->heap);
vtfree(c->block);
vtfree(c->mem);
vtfree(c);
}
static void
vtcachedump(VtCache *c)
{
int i;
VtBlock *b;
for(i=0; i<c->nblock; i++){
b = &c->block[i];
print("cache block %d: type %d score %V iostate %d addr %d ref %d nlock %d\n",
i, b->type, b->score, b->iostate, b->addr, b->ref, b->nlock);
}
}
static void
cachecheck(VtCache *c)
{
u32int size, now;
int i, k, refed;
VtBlock *b;
size = c->blocksize;
now = c->now;
for(i = 0; i < c->nheap; i++){
if(c->heap[i]->heap != i)
sysfatal("mis-heaped at %d: %d", i, c->heap[i]->heap);
if(i > 0 && c->heap[(i - 1) >> 1]->used - now > c->heap[i]->used - now)
sysfatal("bad heap ordering");
k = (i << 1) + 1;
if(k < c->nheap && c->heap[i]->used - now > c->heap[k]->used - now)
sysfatal("bad heap ordering");
k++;
if(k < c->nheap && c->heap[i]->used - now > c->heap[k]->used - now)
sysfatal("bad heap ordering");
}
refed = 0;
for(i = 0; i < c->nblock; i++){
b = &c->block[i];
if(b->data != &c->mem[i * size])
sysfatal("mis-blocked at %d", i);
if(b->ref && b->heap == BadHeap)
refed++;
else if(b->addr != NilBlock)
refed++;
}
assert(c->nheap + refed == c->nblock);
refed = 0;
for(i = 0; i < c->nblock; i++){
b = &c->block[i];
if(b->ref){
refed++;
}
}
}
static int
upheap(int i, VtBlock *b)
{
VtBlock *bb;
u32int now;
int p;
VtCache *c;
c = b->c;
now = c->now;
for(; i != 0; i = p){
p = (i - 1) >> 1;
bb = c->heap[p];
if(b->used - now >= bb->used - now)
break;
c->heap[i] = bb;
bb->heap = i;
}
c->heap[i] = b;
b->heap = i;
return i;
}
static int
downheap(int i, VtBlock *b)
{
VtBlock *bb;
u32int now;
int k;
VtCache *c;
c = b->c;
now = c->now;
for(; ; i = k){
k = (i << 1) + 1;
if(k >= c->nheap)
break;
if(k + 1 < c->nheap && c->heap[k]->used - now > c->heap[k + 1]->used - now)
k++;
bb = c->heap[k];
if(b->used - now <= bb->used - now)
break;
c->heap[i] = bb;
bb->heap = i;
}
c->heap[i] = b;
b->heap = i;
return i;
}
/*
* Delete a block from the heap.
* Called with c->lk held.
*/
static void
heapdel(VtBlock *b)
{
int i, si;
VtCache *c;
c = b->c;
si = b->heap;
if(si == BadHeap)
return;
b->heap = BadHeap;
c->nheap--;
if(si == c->nheap)
return;
b = c->heap[c->nheap];
i = upheap(si, b);
if(i == si)
downheap(i, b);
}
/*
* Insert a block into the heap.
* Called with c->lk held.
*/
static void
heapins(VtBlock *b)
{
assert(b->heap == BadHeap);
upheap(b->c->nheap++, b);
}
/*
* locate the vtBlock with the oldest second to last use.
* remove it from the heap, and fix up the heap.
*/
/* called with c->lk held */
static VtBlock*
vtcachebumpblock(VtCache *c)
{
VtBlock *b;
/*
* locate the vtBlock with the oldest second to last use.
* remove it from the heap, and fix up the heap.
*/
if(c->nheap == 0){
vtcachedump(c);
fprint(2, "vtcachebumpblock: no free blocks in vtCache");
abort();
}
b = c->heap[0];
heapdel(b);
assert(b->heap == BadHeap);
assert(b->ref == 0);
/*
* unchain the vtBlock from hash chain if any
*/
if(b->prev){
*(b->prev) = b->next;
if(b->next)
b->next->prev = b->prev;
b->prev = nil;
}
if(0)fprint(2, "droping %x:%V\n", b->addr, b->score);
/* set vtBlock to a reasonable state */
b->ref = 1;
b->iostate = BioEmpty;
return b;
}
/*
* fetch a local block from the memory cache.
* if it's not there, load it, bumping some other Block.
* if we're out of free blocks, we're screwed.
*/
VtBlock*
vtcachelocal(VtCache *c, u32int addr, int type)
{
VtBlock *b;
if(addr == 0)
sysfatal("vtcachelocal: asked for nonexistent block 0");
if(addr > c->nblock)
sysfatal("vtcachelocal: asked for block #%ud; only %d blocks",
addr, c->nblock);
b = &c->block[addr-1];
if(b->addr == NilBlock || b->iostate != BioLocal)
sysfatal("vtcachelocal: block is not local");
if(b->type != type)
sysfatal("vtcachelocal: block has wrong type %d != %d", b->type, type);
qlock(&c->lk);
b->ref++;
qunlock(&c->lk);
qlock(&b->lk);
b->nlock = 1;
b->pc = getcallerpc(&c);
return b;
}
VtBlock*
vtcacheallocblock(VtCache *c, int type)
{
VtBlock *b;
qlock(&c->lk);
b = vtcachebumpblock(c);
b->iostate = BioLocal;
b->type = type;
b->addr = (b - c->block)+1;
vtzeroextend(type, b->data, 0, c->blocksize);
vtlocaltoglobal(b->addr, b->score);
qunlock(&c->lk);
qlock(&b->lk);
b->nlock = 1;
b->pc = getcallerpc(&c);
return b;
}
/*
* fetch a global (Venti) block from the memory cache.
* if it's not there, load it, bumping some other block.
*/
VtBlock*
vtcacheglobal(VtCache *c, uchar score[VtScoreSize], int type)
{
VtBlock *b;
ulong h;
int n;
u32int addr;
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d from %p\n", score, type, getcallerpc(&c));
addr = vtglobaltolocal(score);
if(addr != NilBlock){
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => local\n", score, type);
b = vtcachelocal(c, addr, type);
if(b)
b->pc = getcallerpc(&c);
return b;
}
h = (u32int)(score[0]|(score[1]<<8)|(score[2]<<16)|(score[3]<<24)) % c->nhash;
/*
* look for the block in the cache
*/
qlock(&c->lk);
for(b = c->hash[h]; b != nil; b = b->next){
if(b->addr != NilBlock || memcmp(b->score, score, VtScoreSize) != 0 || b->type != type)
continue;
heapdel(b);
b->ref++;
qunlock(&c->lk);
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => found in cache %p; locking\n", score, type, b);
qlock(&b->lk);
b->nlock = 1;
if(b->iostate == BioVentiError){
if(chattyventi)
fprint(2, "cached read error for %V\n", score);
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => cache read error\n", score, type);
vtblockput(b);
werrstr("venti i/o error");
return nil;
}
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => found in cache; returning\n", score, type);
b->pc = getcallerpc(&c);
return b;
}
/*
* not found
*/
b = vtcachebumpblock(c);
b->addr = NilBlock;
b->type = type;
memmove(b->score, score, VtScoreSize);
/* chain onto correct hash */
b->next = c->hash[h];
c->hash[h] = b;
if(b->next != nil)
b->next->prev = &b->next;
b->prev = &c->hash[h];
/*
* Lock b before unlocking c, so that others wait while we read.
*
* You might think there is a race between this qlock(b) before qunlock(c)
* and the qlock(c) while holding a qlock(b) in vtblockwrite. However,
* the block here can never be the block in a vtblockwrite, so we're safe.
* We're certainly living on the edge.
*/
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => bumped; locking %p\n", score, type, b);
qlock(&b->lk);
b->nlock = 1;
qunlock(&c->lk);
vtcachenread++;
n = vtread(c->z, score, type, b->data, c->blocksize);
if(n < 0){
if(chattyventi)
fprint(2, "read %V: %r\n", score);
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => bumped; read error\n", score, type);
b->iostate = BioVentiError;
vtblockput(b);
return nil;
}
vtzeroextend(type, b->data, n, c->blocksize);
b->iostate = BioVenti;
b->nlock = 1;
if(vttracelevel)
fprint(2, "vtcacheglobal %V %d => loaded into cache; returning\n", score, type);
b->pc = getcallerpc(&b);
return b;
}
/*
* The thread that has locked b may refer to it by
* multiple names. Nlock counts the number of
* references the locking thread holds. It will call
* vtblockput once per reference.
*/
void
vtblockduplock(VtBlock *b)
{
assert(b->nlock > 0);
b->nlock++;
}
/*
* we're done with the block.
* unlock it. can't use it after calling this.
*/
void
vtblockput(VtBlock* b)
{
VtCache *c;
if(b == nil)
return;
if(0)fprint(2, "vtblockput: %d: %x %d %d\n", getpid(), b->addr, c->nheap, b->iostate);
if(vttracelevel)
fprint(2, "vtblockput %p from %p\n", b, getcallerpc(&b));
if(--b->nlock > 0)
return;
/*
* b->nlock should probably stay at zero while
* the vtBlock is unlocked, but diskThread and vtSleep
* conspire to assume that they can just qlock(&b->lk); vtblockput(b),
* so we have to keep b->nlock set to 1 even
* when the vtBlock is unlocked.
*/
assert(b->nlock == 0);
b->nlock = 1;
qunlock(&b->lk);
c = b->c;
qlock(&c->lk);
if(--b->ref > 0){
qunlock(&c->lk);
return;
}
assert(b->ref == 0);
switch(b->iostate){
case BioVenti:
/*if(b->addr != NilBlock) print("blockput %d\n", b->addr); */
b->used = c->now++;
/* fall through */
case BioVentiError:
heapins(b);
break;
case BioLocal:
break;
}
qunlock(&c->lk);
}
int
vtblockwrite(VtBlock *b)
{
uchar score[VtScoreSize];
VtCache *c;
uint h;
int n;
if(b->iostate != BioLocal){
werrstr("vtblockwrite: not a local block");
return -1;
}
c = b->c;
n = vtzerotruncate(b->type, b->data, c->blocksize);
vtcachenwrite++;
if(c->write(c->z, score, b->type, b->data, n) < 0)
return -1;
memmove(b->score, score, VtScoreSize);
qlock(&c->lk);
b->addr = NilBlock; /* now on venti */
b->iostate = BioVenti;
h = (u32int)(score[0]|(score[1]<<8)|(score[2]<<16)|(score[3]<<24)) % c->nhash;
b->next = c->hash[h];
c->hash[h] = b;
if(b->next != nil)
b->next->prev = &b->next;
b->prev = &c->hash[h];
qunlock(&c->lk);
return 0;
}
uint
vtcacheblocksize(VtCache *c)
{
return c->blocksize;
}
VtBlock*
vtblockcopy(VtBlock *b)
{
VtBlock *bb;
vtcachencopy++;
bb = vtcacheallocblock(b->c, b->type);
if(bb == nil){
vtblockput(b);
return nil;
}
memmove(bb->data, b->data, b->c->blocksize);
vtblockput(b);
bb->pc = getcallerpc(&b);
return bb;
}
void
vtlocaltoglobal(u32int addr, uchar score[VtScoreSize])
{
memset(score, 0, 16);
score[16] = addr>>24;
score[17] = addr>>16;
score[18] = addr>>8;
score[19] = addr;
}
u32int
vtglobaltolocal(uchar score[VtScoreSize])
{
static uchar zero[16];
if(memcmp(score, zero, 16) != 0)
return NilBlock;
return (score[16]<<24)|(score[17]<<16)|(score[18]<<8)|score[19];
}