ref: 333ae58f37c2c8f79f7d7078283a30e42c4d7a27
dir: /cache.c/
#include "stdinc.h"
#include "dat.h"
#include "fns.h"
#include "error.h"
#include "9.h" /* for cacheFlush */
typedef struct FreeList FreeList;
typedef struct BAddr BAddr;
enum {
BadHeap = ~0,
};
/*
* Store data to the memory cache in c->size blocks
* with the block zero extended to fill it out. When writing to
* Venti, the block will be zero truncated. The walker will also check
* that the block fits within psize or dsize as the case may be.
*/
struct Cache
{
QLock lk;
int ref;
int mode;
Disk *disk;
int size; /* block size */
int ndmap; /* size of per-block dirty pointer map used in blockWrite */
VtConn *z;
u32int now; /* ticks for usage timestamps */
Block **heads; /* hash table for finding address */
int nheap; /* number of available victims */
Block **heap; /* heap for locating victims */
long nblocks; /* number of blocks allocated */
Block *blocks; /* array of block descriptors */
u8int *mem; /* memory for all block data & blists */
BList *blfree;
Rendez blrend;
int ndirty; /* number of dirty blocks in the cache */
int maxdirty; /* max number of dirty blocks */
u32int vers;
long hashSize;
FreeList *fl;
Rendez die; /* daemon threads should die when QLock != nil */
Rendez flush;
Rendez flushwait;
Rendez heapwait;
BAddr *baddr;
int bw, br, be;
int nflush;
Periodic *sync;
/* unlink daemon */
BList *uhead;
BList *utail;
Rendez unlink;
/* block counts */
int nused;
int ndisk;
};
struct BList {
int part;
u32int addr;
uchar type;
u32int tag;
u32int epoch;
u32int vers;
int recurse; /* for block unlink */
/* for roll back */
int index; /* -1 indicates not valid */
union {
uchar score[VtScoreSize];
uchar entry[VtEntrySize];
} old;
BList *next;
};
struct BAddr {
int part;
u32int addr;
u32int vers;
};
struct FreeList {
QLock lk;
u32int last; /* last block allocated */
u32int end; /* end of data partition */
u32int nused; /* number of used blocks */
u32int epochLow; /* low epoch when last updated nused */
};
static FreeList *flAlloc(u32int end);
static void flFree(FreeList *fl);
static Block *cacheBumpBlock(Cache *c);
static void heapDel(Block*);
static void heapIns(Block*);
static void cacheCheck(Cache*);
static void unlinkThread(void *a);
static void flushThread(void *a);
static void unlinkBody(Cache *c);
static int cacheFlushBlock(Cache *c);
static void cacheSync(void*);
static BList *blistAlloc(Block*);
static void blistFree(Cache*, BList*);
static void doRemoveLink(Cache*, BList*);
/*
* Mapping from local block type to Venti type
*/
int vtType[BtMax] = {
VtDataType, /* BtData | 0 */
VtDataType+1, /* BtData | 1 */
VtDataType+2, /* BtData | 2 */
VtDataType+3, /* BtData | 3 */
VtDataType+4, /* BtData | 4 */
VtDataType+5, /* BtData | 5 */
VtDataType+6, /* BtData | 6 */
VtDataType+7, /* BtData | 7 */
VtDirType, /* BtDir | 0 */
VtDirType+1, /* BtDir | 1 */
VtDirType+2, /* BtDir | 2 */
VtDirType+3, /* BtDir | 3 */
VtDirType+4, /* BtDir | 4 */
VtDirType+5, /* BtDir | 5 */
VtDirType+6, /* BtDir | 6 */
VtDirType+7, /* BtDir | 7 */
};
/*
* Allocate the memory cache.
*/
Cache *
cacheAlloc(Disk *disk, VtConn *z, ulong nblocks, int mode)
{
int i;
Cache *c;
Block *b;
BList *bl;
u8int *p;
int nbl;
c = vtmallocz(sizeof(Cache));
/* reasonable number of BList elements */
nbl = nblocks * 4;
c->ref = 1;
c->disk = disk;
c->z = z;
c->size = diskBlockSize(disk);
bwatchSetBlockSize(c->size);
/* round c->size up to be a nice multiple */
c->size = (c->size + 127) & ~127;
c->ndmap = (c->size/20 + 7) / 8;
c->nblocks = nblocks;
c->hashSize = nblocks;
c->heads = vtmallocz(c->hashSize*sizeof(Block*));
c->heap = vtmallocz(nblocks*sizeof(Block*));
c->blocks = vtmallocz(nblocks*sizeof(Block));
c->mem = vtmallocz(nblocks * (c->size + c->ndmap) + nbl * sizeof(BList));
c->baddr = vtmallocz(nblocks * sizeof(BAddr));
c->mode = mode;
c->vers++;
p = c->mem;
for(i = 0; i < nblocks; i++){
b = &c->blocks[i];
b->c = c;
b->data = p;
b->heap = i;
b->ioready.l = &b->lk;
c->heap[i] = b;
p += c->size;
}
c->nheap = nblocks;
for(i = 0; i < nbl; i++){
bl = (BList*)p;
bl->next = c->blfree;
c->blfree = bl;
p += sizeof(BList);
}
/* separate loop to keep blocks and blists reasonably aligned */
for(i = 0; i < nblocks; i++){
b = &c->blocks[i];
b->dmap = p;
p += c->ndmap;
}
c->blrend.l = &c->lk;
c->maxdirty = nblocks*(DirtyPercentage*0.01);
c->fl = flAlloc(diskSize(disk, PartData));
c->unlink.l = &c->lk;
c->flush.l = &c->lk;
c->flushwait.l = &c->lk;
c->heapwait.l = &c->lk;
c->sync = periodicAlloc(cacheSync, c, 30*1000);
if(mode == OReadWrite){
c->ref += 2;
proccreate(unlinkThread, c, STACK);
proccreate(flushThread, c, STACK);
}
cacheCheck(c);
return c;
}
/*
* Free the whole memory cache, flushing all dirty blocks to the disk.
*/
void
cacheFree(Cache *c)
{
int i;
/* kill off daemon threads */
qlock(&c->lk);
c->die.l = &c->lk;
periodicKill(c->sync);
rwakeup(&c->flush);
rwakeup(&c->unlink);
while(c->ref > 1)
rsleep(&c->die);
/* flush everything out */
do {
unlinkBody(c);
qunlock(&c->lk);
while(cacheFlushBlock(c))
;
diskFlush(c->disk);
qlock(&c->lk);
} while(c->uhead || c->ndirty);
qunlock(&c->lk);
cacheCheck(c);
for(i = 0; i < c->nblocks; i++){
assert(c->blocks[i].ref == 0);
}
flFree(c->fl);
vtfree(c->baddr);
vtfree(c->heads);
vtfree(c->blocks);
vtfree(c->mem);
diskFree(c->disk);
/* don't close vtSession */
vtfree(c);
}
static void
cacheDump(Cache *c)
{
int i;
Block *b;
for(i = 0; i < c->nblocks; i++){
b = &c->blocks[i];
fprint(2, "%d. p=%d a=%ud %V t=%d ref=%d state=%s io=%s pc=%#p\n",
i, b->part, b->addr, b->score, b->l.type, b->ref,
bsStr(b->l.state), bioStr(b->iostate), b->pc);
}
}
static void
cacheCheck(Cache *c)
{
u32int size, now;
int i, k, refed;
static uchar zero[VtScoreSize];
Block *b;
size = c->size;
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->nblocks; i++){
b = &c->blocks[i];
if(b->data != &c->mem[i * size])
sysfatal("mis-blocked at %d", i);
if(b->ref && b->heap == BadHeap){
refed++;
}
}
if(c->nheap + refed != c->nblocks){
fprint(2, "%s: cacheCheck: nheap %d refed %d nblocks %ld\n", argv0, c->nheap, refed, c->nblocks);
cacheDump(c);
}
assert(c->nheap + refed == c->nblocks);
refed = 0;
for(i = 0; i < c->nblocks; i++){
b = &c->blocks[i];
if(b->ref){
if(1)fprint(2, "%s: p=%d a=%ud %V ref=%d %L\n", argv0, b->part, b->addr, b->score, b->ref, &b->l);
refed++;
}
}
if(refed > 0)fprint(2, "%s: cacheCheck: in used %d\n", argv0, refed);
}
/*
* locate the block with the oldest second to last use.
* remove it from the heap, and fix up the heap.
*/
/* called with c->lk held */
static Block *
cacheBumpBlock(Cache *c)
{
int printed;
Block *b;
/*
* locate the block with the oldest second to last use.
* remove it from the heap, and fix up the heap.
*/
printed = 0;
if(c->nheap == 0){
while(c->nheap == 0){
rwakeup(&c->flush);
rsleep(&c->heapwait);
if(c->nheap == 0){
printed = 1;
fprint(2, "%s: entire cache is busy, %d dirty "
"-- waking flush thread\n",
argv0, c->ndirty);
}
}
if(printed)
fprint(2, "%s: cache is okay again, %d dirty\n",
argv0, c->ndirty);
}
b = c->heap[0];
heapDel(b);
assert(b->heap == BadHeap);
assert(b->ref == 0);
assert(b->iostate != BioDirty && b->iostate != BioReading && b->iostate != BioWriting);
assert(b->prior == nil);
assert(b->uhead == nil);
/*
* unchain the block from hash chain
*/
if(b->prev){
*(b->prev) = b->next;
if(b->next)
b->next->prev = b->prev;
b->prev = nil;
}
if(0)fprint(2, "%s: dropping %d:%x:%V\n", argv0, b->part, b->addr, b->score);
/* set block to a reasonable state */
b->ref = 1;
b->part = PartError;
memset(&b->l, 0, sizeof(b->l));
b->iostate = BioEmpty;
return b;
}
/*
* look for a particular version of the block in the memory cache.
*/
static Block *
_cacheLocalLookup(Cache *c, int part, u32int addr, u32int vers,
int waitlock, int *lockfailure)
{
Block *b;
ulong h;
h = addr % c->hashSize;
if(lockfailure)
*lockfailure = 0;
/*
* look for the block in the cache
*/
qlock(&c->lk);
for(b = c->heads[h]; b != nil; b = b->next){
if(b->part == part && b->addr == addr)
break;
}
if(b == nil || b->vers != vers){
qunlock(&c->lk);
return nil;
}
if(!waitlock && !canqlock(&b->lk)){
*lockfailure = 1;
qunlock(&c->lk);
return nil;
}
heapDel(b);
b->ref++;
qunlock(&c->lk);
bwatchLock(b);
if(waitlock)
qlock(&b->lk);
b->nlock = 1;
for(;;){
switch(b->iostate){
default:
abort();
case BioEmpty:
case BioLabel:
case BioClean:
case BioDirty:
if(b->vers != vers){
blockPut(b);
return nil;
}
return b;
case BioReading:
case BioWriting:
rsleep(&b->ioready);
break;
case BioVentiError:
blockPut(b);
werrstr("venti i/o error block 0x%.8ux", addr);
return nil;
case BioReadError:
blockPut(b);
werrstr("error reading block 0x%.8ux", addr);
return nil;
}
}
/* NOT REACHED */
}
static Block*
cacheLocalLookup(Cache *c, int part, u32int addr, u32int vers)
{
return _cacheLocalLookup(c, part, addr, vers, Waitlock, 0);
}
/*
* fetch a local (on-disk) block from the memory cache.
* if it's not there, load it, bumping some other block.
*/
Block *
_cacheLocal(Cache *c, int part, u32int addr, int mode, u32int epoch)
{
Block *b;
ulong h;
assert(part != PartVenti);
h = addr % c->hashSize;
/*
* look for the block in the cache
*/
qlock(&c->lk);
for(b = c->heads[h]; b != nil; b = b->next){
if(b->part != part || b->addr != addr)
continue;
if(epoch && b->l.epoch != epoch){
fprint(2, "%s: _cacheLocal want epoch %ud got %ud\n", argv0, epoch, b->l.epoch);
qunlock(&c->lk);
werrstr(ELabelMismatch);
return nil;
}
heapDel(b);
b->ref++;
break;
}
if(b == nil){
b = cacheBumpBlock(c);
b->part = part;
b->addr = addr;
localToGlobal(addr, b->score);
/* chain onto correct hash */
b->next = c->heads[h];
c->heads[h] = b;
if(b->next != nil)
b->next->prev = &b->next;
b->prev = &c->heads[h];
}
qunlock(&c->lk);
/*
* BUG: what if the epoch changes right here?
* In the worst case, we could end up in some weird
* lock loop, because the block we want no longer exists,
* and instead we're trying to lock a block we have no
* business grabbing.
*
* For now, I'm not going to worry about it.
*/
if(0)fprint(2, "%s: cacheLocal: %d: %d %x\n", argv0, getpid(), b->part, b->addr);
bwatchLock(b);
qlock(&b->lk);
b->nlock = 1;
if(part == PartData && b->iostate == BioEmpty){
if(!readLabel(c, &b->l, addr)){
blockPut(b);
return nil;
}
blockSetIOState(b, BioLabel);
}
if(epoch && b->l.epoch != epoch){
blockPut(b);
fprint(2, "%s: _cacheLocal want epoch %ud got %ud\n", argv0, epoch, b->l.epoch);
werrstr(ELabelMismatch);
return nil;
}
b->pc = getcallerpc(&c);
for(;;){
switch(b->iostate){
default:
abort();
case BioLabel:
if(mode == OOverWrite)
/*
* leave iostate as BioLabel because data
* hasn't been read.
*/
return b;
/* fall through */
case BioEmpty:
diskRead(c->disk, b);
rsleep(&b->ioready);
break;
case BioClean:
case BioDirty:
return b;
case BioReading:
case BioWriting:
rsleep(&b->ioready);
break;
case BioReadError:
blockSetIOState(b, BioEmpty);
blockPut(b);
werrstr("error reading block 0x%.8ux", addr);
return nil;
}
}
/* NOT REACHED */
}
Block *
cacheLocal(Cache *c, int part, u32int addr, int mode)
{
return _cacheLocal(c, part, addr, mode, 0);
}
/*
* fetch a local (on-disk) block from the memory cache.
* if it's not there, load it, bumping some other block.
* check tag and type.
*/
Block *
cacheLocalData(Cache *c, u32int addr, int type, u32int tag, int mode, u32int epoch)
{
Block *b;
b = _cacheLocal(c, PartData, addr, mode, epoch);
if(b == nil)
return nil;
if(b->l.type != type || b->l.tag != tag){
fprint(2, "%s: cacheLocalData: addr=%d type got %d exp %d: tag got %ux exp %ux\n",
argv0, addr, b->l.type, type, b->l.tag, tag);
werrstr(ELabelMismatch);
blockPut(b);
return nil;
}
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.
* check tag and type if it's really a local block in disguise.
*/
Block *
cacheGlobal(Cache *c, uchar score[VtScoreSize], int type, u32int tag, int mode)
{
int n;
Block *b;
ulong h;
u32int addr;
addr = globalToLocal(score);
if(addr != NilBlock){
b = cacheLocalData(c, addr, type, tag, mode, 0);
if(b)
b->pc = getcallerpc(&c);
return b;
}
h = (u32int)(score[0]|(score[1]<<8)|(score[2]<<16)|(score[3]<<24)) % c->hashSize;
/*
* look for the block in the cache
*/
qlock(&c->lk);
for(b = c->heads[h]; b != nil; b = b->next){
if(b->part != PartVenti || memcmp(b->score, score, VtScoreSize) != 0 || b->l.type != type)
continue;
heapDel(b);
b->ref++;
break;
}
if(b == nil){
if(0)fprint(2, "%s: cacheGlobal %V %d\n", argv0, score, type);
b = cacheBumpBlock(c);
b->part = PartVenti;
b->addr = NilBlock;
b->l.type = type;
memmove(b->score, score, VtScoreSize);
/* chain onto correct hash */
b->next = c->heads[h];
c->heads[h] = b;
if(b->next != nil)
b->next->prev = &b->next;
b->prev = &c->heads[h];
}
qunlock(&c->lk);
bwatchLock(b);
qlock(&b->lk);
b->nlock = 1;
b->pc = getcallerpc(&c);
switch(b->iostate){
default:
abort();
case BioEmpty:
n = vtread(c->z, score, vtType[type], b->data, c->size);
if(n < 0 || vtsha1check(score, b->data, n) < 0){
blockSetIOState(b, BioVentiError);
blockPut(b);
werrstr(
"venti error reading block %V or wrong score: %r",
score);
return nil;
}
vtzeroextend(vtType[type], b->data, n, c->size);
blockSetIOState(b, BioClean);
return b;
case BioClean:
return b;
case BioVentiError:
blockPut(b);
werrstr("venti i/o error or wrong score, block %V", score);
return nil;
case BioReadError:
blockPut(b);
werrstr("error reading block %V", b->score);
return nil;
}
/* NOT REACHED */
}
/*
* allocate a new on-disk block and load it into the memory cache.
* BUG: if the disk is full, should we flush some of it to Venti?
*/
static u32int lastAlloc;
Block *
cacheAllocBlock(Cache *c, int type, u32int tag, u32int epoch, u32int epochLow)
{
FreeList *fl;
u32int addr;
Block *b;
int n, nwrap;
Label lab;
n = c->size / LabelSize;
fl = c->fl;
qlock(&fl->lk);
addr = fl->last;
nwrap = 0;
NotFound:
b = cacheLocal(c, PartLabel, addr/n, OReadOnly);
if(b == nil){
fprint(2, "%s: cacheAllocBlock: xxx %r\n", argv0);
qunlock(&fl->lk);
return nil;
}
for(;;){
if(++addr >= fl->end){
addr = 0;
if(++nwrap >= 2){
blockPut(b);
werrstr("disk is full");
/*
* try to avoid a continuous spew of console
* messages.
*/
if (fl->last != 0)
fprint(2, "%s: cacheAllocBlock: xxx1 %r\n",
argv0);
fl->last = 0;
qunlock(&fl->lk);
return nil;
}
}
if(addr%n == 0){
blockPut(b);
b = cacheLocal(c, PartLabel, addr/n, OReadOnly);
if(b == nil){
fl->last = addr;
fprint(2, "%s: cacheAllocBlock: xxx2 %r\n", argv0);
qunlock(&fl->lk);
return nil;
}
}
if(!labelUnpack(&lab, b->data, addr%n))
continue;
if(lab.state == BsFree)
goto Found;
if(lab.state&BsClosed)
if(lab.epochClose <= epochLow || lab.epoch==lab.epochClose)
goto Found;
}
Found:
blockPut(b);
b = cacheLocal(c, PartData, addr, OOverWrite);
if(b == nil){
fprint(2, "%s: cacheAllocBlock: xxx3 %r\n", argv0);
return nil;
}
if(!(b->iostate == BioLabel || b->iostate == BioClean)){
if(0)fprint(2, "%s: cacheAllocBlock addr %ud iostate %s label %L\n",
argv0, addr, bioStr(b->iostate), &lab);
blockPut(b);
goto NotFound;
}
fl->last = addr;
lab.type = type;
lab.tag = tag;
lab.state = BsAlloc;
lab.epoch = epoch;
lab.epochClose = ~(u32int)0;
if(!blockSetLabel(b, &lab, 1)){
fprint(2, "%s: cacheAllocBlock: xxx4 %r\n", argv0);
blockPut(b);
return nil;
}
vtzeroextend(vtType[type], b->data, 0, c->size);
if(0)diskWrite(c->disk, b);
if(0)fprint(2, "%s: fsAlloc %ud type=%d tag = %ux\n", argv0, addr, type, tag);
lastAlloc = addr;
fl->nused++;
qunlock(&fl->lk);
b->pc = getcallerpc(&c);
return b;
}
int
cacheDirty(Cache *c)
{
return c->ndirty;
}
void
cacheCountUsed(Cache *c, u32int epochLow, u32int *used, u32int *total, u32int *bsize)
{
int n;
u32int addr, nused;
Block *b;
Label lab;
FreeList *fl;
fl = c->fl;
n = c->size / LabelSize;
*bsize = c->size;
qlock(&fl->lk);
if(fl->epochLow == epochLow){
*used = fl->nused;
*total = fl->end;
qunlock(&fl->lk);
return;
}
b = nil;
nused = 0;
for(addr=0; addr<fl->end; addr++){
if(addr%n == 0){
blockPut(b);
b = cacheLocal(c, PartLabel, addr/n, OReadOnly);
if(b == nil){
fprint(2, "%s: flCountUsed: loading %ux: %r\n",
argv0, addr/n);
break;
}
}
if(!labelUnpack(&lab, b->data, addr%n))
continue;
if(lab.state == BsFree)
continue;
if(lab.state&BsClosed)
if(lab.epochClose <= epochLow || lab.epoch==lab.epochClose)
continue;
nused++;
}
blockPut(b);
if(addr == fl->end){
fl->nused = nused;
fl->epochLow = epochLow;
}
*used = nused;
*total = fl->end;
qunlock(&fl->lk);
return;
}
static FreeList *
flAlloc(u32int end)
{
FreeList *fl;
fl = vtmallocz(sizeof(*fl));
fl->last = 0;
fl->end = end;
return fl;
}
static void
flFree(FreeList *fl)
{
vtfree(fl);
}
u32int
cacheLocalSize(Cache *c, int part)
{
return diskSize(c->disk, part);
}
/*
* 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
* blockPut once per reference.
*/
void
blockDupLock(Block *b)
{
assert(b->nlock > 0);
b->nlock++;
}
/*
* we're done with the block.
* unlock it. can't use it after calling this.
*/
void
blockPut(Block* b)
{
Cache *c;
if(b == nil)
return;
if(0)fprint(2, "%s: blockPut: %d: %d %x %d %s\n", argv0, getpid(), b->part, b->addr, c->nheap, bioStr(b->iostate));
if(b->iostate == BioDirty)
bwatchDependency(b);
if(--b->nlock > 0)
return;
/*
* b->nlock should probably stay at zero while
* the block is unlocked, but diskThread and rsleep
* conspire to assume that they can just qlock(&b->lk); blockPut(b),
* so we have to keep b->nlock set to 1 even
* when the block is unlocked.
*/
assert(b->nlock == 0);
b->nlock = 1;
// b->pc = 0;
bwatchUnlock(b);
qunlock(&b->lk);
c = b->c;
qlock(&c->lk);
if(--b->ref > 0){
qunlock(&c->lk);
return;
}
assert(b->ref == 0);
switch(b->iostate){
default:
b->used = c->now++;
heapIns(b);
break;
case BioEmpty:
case BioLabel:
if(c->nheap == 0)
b->used = c->now++;
else
b->used = c->heap[0]->used;
heapIns(b);
break;
case BioDirty:
break;
}
qunlock(&c->lk);
}
/*
* set the label associated with a block.
*/
Block*
_blockSetLabel(Block *b, Label *l)
{
int lpb;
Block *bb;
u32int a;
Cache *c;
c = b->c;
assert(b->part == PartData);
assert(b->iostate == BioLabel || b->iostate == BioClean || b->iostate == BioDirty);
lpb = c->size / LabelSize;
a = b->addr / lpb;
bb = cacheLocal(c, PartLabel, a, OReadWrite);
if(bb == nil){
blockPut(b);
return nil;
}
b->l = *l;
labelPack(l, bb->data, b->addr%lpb);
blockDirty(bb);
return bb;
}
int
blockSetLabel(Block *b, Label *l, int allocating)
{
Block *lb;
Label oldl;
oldl = b->l;
lb = _blockSetLabel(b, l);
if(lb == nil)
return 0;
/*
* If we're allocating the block, make sure the label (bl)
* goes to disk before the data block (b) itself. This is to help
* the blocks that in turn depend on b.
*
* Suppose bx depends on (must be written out after) b.
* Once we write b we'll think it's safe to write bx.
* Bx can't get at b unless it has a valid label, though.
*
* Allocation is the only case in which having a current label
* is vital because:
*
* - l.type is set at allocation and never changes.
* - l.tag is set at allocation and never changes.
* - l.state is not checked when we load blocks.
* - the archiver cares deeply about l.state being
* BaActive vs. BaCopied, but that's handled
* by direct calls to _blockSetLabel.
*/
if(allocating)
blockDependency(b, lb, -1, nil, nil);
blockPut(lb);
return 1;
}
/*
* Record that bb must be written out before b.
* If index is given, we're about to overwrite the score/e
* at that index in the block. Save the old value so we
* can write a safer ``old'' version of the block if pressed.
*/
void
blockDependency(Block *b, Block *bb, int index, uchar *score, Entry *e)
{
BList *p;
if(bb->iostate == BioClean)
return;
/*
* Dependencies for blocks containing Entry structures
* or scores must always be explained. The problem with
* only explaining some of them is this. Suppose we have two
* dependencies for the same field, the first explained
* and the second not. We try to write the block when the first
* dependency is not written but the second is. We will roll back
* the first change even though the second trumps it.
*/
if(index == -1 && bb->part == PartData)
assert(b->l.type == BtData);
if(bb->iostate != BioDirty){
fprint(2, "%s: %d:%x:%d iostate is %d in blockDependency\n",
argv0, bb->part, bb->addr, bb->l.type, bb->iostate);
abort();
}
p = blistAlloc(bb);
if(p == nil)
return;
assert(bb->iostate == BioDirty);
if(0)fprint(2, "%s: %d:%x:%d depends on %d:%x:%d\n", argv0, b->part, b->addr, b->l.type, bb->part, bb->addr, bb->l.type);
p->part = bb->part;
p->addr = bb->addr;
p->type = bb->l.type;
p->vers = bb->vers;
p->index = index;
if(p->index >= 0){
/*
* This test would just be b->l.type==BtDir except
* we need to exclude the super block.
*/
if(b->l.type == BtDir && b->part == PartData)
entryPack(e, p->old.entry, 0);
else
memmove(p->old.score, score, VtScoreSize);
}
p->next = b->prior;
b->prior = p;
}
/*
* Mark an in-memory block as dirty. If there are too many
* dirty blocks, start writing some out to disk.
*
* If there were way too many dirty blocks, we used to
* try to do some flushing ourselves, but it's just too dangerous --
* it implies that the callers cannot have any of our priors locked,
* but this is hard to avoid in some cases.
*/
int
blockDirty(Block *b)
{
Cache *c;
c = b->c;
assert(b->part != PartVenti);
if(b->iostate == BioDirty)
return 1;
assert(b->iostate == BioClean || b->iostate == BioLabel);
qlock(&c->lk);
b->iostate = BioDirty;
c->ndirty++;
if(c->ndirty > (c->maxdirty>>1))
rwakeup(&c->flush);
qunlock(&c->lk);
return 1;
}
/*
* We've decided to write out b. Maybe b has some pointers to blocks
* that haven't yet been written to disk. If so, construct a slightly out-of-date
* copy of b that is safe to write out. (diskThread will make sure the block
* remains marked as dirty.)
*/
uchar *
blockRollback(Block *b, uchar *buf)
{
u32int addr;
BList *p;
Super super;
/* easy case */
if(b->prior == nil)
return b->data;
memmove(buf, b->data, b->c->size);
for(p=b->prior; p; p=p->next){
/*
* we know p->index >= 0 because blockWrite has vetted this block for us.
*/
assert(p->index >= 0);
assert(b->part == PartSuper || (b->part == PartData && b->l.type != BtData));
if(b->part == PartSuper){
assert(p->index == 0);
superUnpack(&super, buf);
addr = globalToLocal(p->old.score);
if(addr == NilBlock){
fprint(2, "%s: rolling back super block: "
"bad replacement addr %V\n",
argv0, p->old.score);
abort();
}
super.active = addr;
superPack(&super, buf);
continue;
}
if(b->l.type == BtDir)
memmove(buf+p->index*VtEntrySize, p->old.entry, VtEntrySize);
else
memmove(buf+p->index*VtScoreSize, p->old.score, VtScoreSize);
}
return buf;
}
/*
* Try to write block b.
* If b depends on other blocks:
*
* If the block has been written out, remove the dependency.
* If the dependency is replaced by a more recent dependency,
* throw it out.
* If we know how to write out an old version of b that doesn't
* depend on it, do that.
*
* Otherwise, bail.
*/
int
blockWrite(Block *b, int waitlock)
{
uchar *dmap;
Cache *c;
BList *p, **pp;
Block *bb;
int lockfail;
c = b->c;
if(b->iostate != BioDirty)
return 1;
dmap = b->dmap;
memset(dmap, 0, c->ndmap);
pp = &b->prior;
for(p=*pp; p; p=*pp){
if(p->index >= 0){
/* more recent dependency has succeeded; this one can go */
if(dmap[p->index/8] & (1<<(p->index%8)))
goto ignblock;
}
lockfail = 0;
bb = _cacheLocalLookup(c, p->part, p->addr, p->vers, waitlock,
&lockfail);
if(bb == nil){
if(lockfail)
return 0;
/* block not in cache => was written already */
dmap[p->index/8] |= 1<<(p->index%8);
goto ignblock;
}
/*
* same version of block is still in cache.
*
* the assertion is true because the block still has version p->vers,
* which means it hasn't been written out since we last saw it.
*/
if(bb->iostate != BioDirty){
fprint(2, "%s: %d:%x:%d iostate is %d in blockWrite\n",
argv0, bb->part, bb->addr, bb->l.type, bb->iostate);
/* probably BioWriting if it happens? */
if(bb->iostate == BioClean){
blockPut(bb);
goto ignblock;
}
}
blockPut(bb);
if(p->index < 0){
/*
* We don't know how to temporarily undo
* b's dependency on bb, so just don't write b yet.
*/
if(0) fprint(2, "%s: blockWrite skipping %d %x %d %d; need to write %d %x %d\n",
argv0, b->part, b->addr, b->vers, b->l.type, p->part, p->addr, bb->vers);
return 0;
}
/* keep walking down the list */
pp = &p->next;
continue;
ignblock:
*pp = p->next;
blistFree(c, p);
continue;
}
/*
* DiskWrite must never be called with a double-locked block.
* This call to diskWrite is okay because blockWrite is only called
* from the cache flush thread, which never double-locks a block.
*/
diskWrite(c->disk, b);
return 1;
}
/*
* Change the I/O state of block b.
* Just an assignment except for magic in
* switch statement (read comments there).
*/
void
blockSetIOState(Block *b, int iostate)
{
int dowakeup;
Cache *c;
BList *p, *q;
if(0) fprint(2, "%s: iostate part=%d addr=%x %s->%s\n", argv0, b->part, b->addr, bioStr(b->iostate), bioStr(iostate));
c = b->c;
dowakeup = 0;
switch(iostate){
default:
abort();
case BioEmpty:
assert(!b->uhead);
break;
case BioLabel:
assert(!b->uhead);
break;
case BioClean:
bwatchDependency(b);
/*
* If b->prior is set, it means a write just finished.
* The prior list isn't needed anymore.
*/
for(p=b->prior; p; p=q){
q = p->next;
blistFree(c, p);
}
b->prior = nil;
/*
* Freeing a block or just finished a write.
* Move the blocks from the per-block unlink
* queue to the cache unlink queue.
*/
if(b->iostate == BioDirty || b->iostate == BioWriting){
qlock(&c->lk);
c->ndirty--;
b->iostate = iostate; /* change here to keep in sync with ndirty */
b->vers = c->vers++;
if(b->uhead){
/* add unlink blocks to unlink queue */
if(c->uhead == nil){
c->uhead = b->uhead;
rwakeup(&c->unlink);
}else
c->utail->next = b->uhead;
c->utail = b->utail;
b->uhead = nil;
}
qunlock(&c->lk);
}
assert(!b->uhead);
dowakeup = 1;
break;
case BioDirty:
/*
* Wrote out an old version of the block (see blockRollback).
* Bump a version count, leave it dirty.
*/
if(b->iostate == BioWriting){
qlock(&c->lk);
b->vers = c->vers++;
qunlock(&c->lk);
dowakeup = 1;
}
break;
case BioReading:
case BioWriting:
/*
* Adding block to disk queue. Bump reference count.
* diskThread decs the count later by calling blockPut.
* This is here because we need to lock c->lk to
* manipulate the ref count.
*/
qlock(&c->lk);
b->ref++;
qunlock(&c->lk);
break;
case BioReadError:
case BioVentiError:
/*
* Oops.
*/
dowakeup = 1;
break;
}
b->iostate = iostate;
/*
* Now that the state has changed, we can wake the waiters.
*/
if(dowakeup)
rwakeupall(&b->ioready);
}
/*
* The active file system is a tree of blocks.
* When we add snapshots to the mix, the entire file system
* becomes a dag and thus requires a bit more care.
*
* The life of the file system is divided into epochs. A snapshot
* ends one epoch and begins the next. Each file system block
* is marked with the epoch in which it was created (b.epoch).
* When the block is unlinked from the file system (closed), it is marked
* with the epoch in which it was removed (b.epochClose).
* Once we have discarded or archived all snapshots up to
* b.epochClose, we can reclaim the block.
*
* If a block was created in a past epoch but is not yet closed,
* it is treated as copy-on-write. Of course, in order to insert the
* new pointer into the tree, the parent must be made writable,
* and so on up the tree. The recursion stops because the root
* block is always writable.
*
* If blocks are never closed, they will never be reused, and
* we will run out of disk space. But marking a block as closed
* requires some care about dependencies and write orderings.
*
* (1) If a block p points at a copy-on-write block b and we
* copy b to create bb, then p must be written out after bb and
* lbb (bb's label block).
*
* (2) We have to mark b as closed, but only after we switch
* the pointer, so lb must be written out after p. In fact, we
* can't even update the in-memory copy, or the cache might
* mistakenly give out b for reuse before p gets written.
*
* CacheAllocBlock's call to blockSetLabel records a "bb after lbb" dependency.
* The caller is expected to record a "p after bb" dependency
* to finish (1), and also expected to call blockRemoveLink
* to arrange for (2) to happen once p is written.
*
* Until (2) happens, some pieces of the code (e.g., the archiver)
* still need to know whether a block has been copied, so we
* set the BsCopied bit in the label and force that to disk *before*
* the copy gets written out.
*/
Block*
blockCopy(Block *b, u32int tag, u32int ehi, u32int elo)
{
Block *bb, *lb;
Label l;
if((b->l.state&BsClosed) || b->l.epoch >= ehi)
fprint(2, "%s: blockCopy %#ux %L but fs is [%ud,%ud]\n",
argv0, b->addr, &b->l, elo, ehi);
bb = cacheAllocBlock(b->c, b->l.type, tag, ehi, elo);
if(bb == nil){
blockPut(b);
return nil;
}
/*
* Update label so we know the block has been copied.
* (It will be marked closed once it has been unlinked from
* the tree.) This must follow cacheAllocBlock since we
* can't be holding onto lb when we call cacheAllocBlock.
*/
if((b->l.state&BsCopied)==0)
if(b->part == PartData){ /* not the superblock */
l = b->l;
l.state |= BsCopied;
lb = _blockSetLabel(b, &l);
if(lb == nil){
/* can't set label => can't copy block */
blockPut(b);
l.type = BtMax;
l.state = BsFree;
l.epoch = 0;
l.epochClose = 0;
l.tag = 0;
blockSetLabel(bb, &l, 0);
blockPut(bb);
return nil;
}
blockDependency(bb, lb, -1, nil, nil);
blockPut(lb);
}
memmove(bb->data, b->data, b->c->size);
blockDirty(bb);
blockPut(b);
return bb;
}
/*
* Block b once pointed at the block bb at addr/type/tag, but no longer does.
* If recurse is set, we are unlinking all of bb's children as well.
*
* We can't reclaim bb (or its kids) until the block b gets written to disk. We add
* the relevant information to b's list of unlinked blocks. Once b is written,
* the list will be queued for processing.
*
* If b depends on bb, it doesn't anymore, so we remove bb from the prior list.
*/
void
blockRemoveLink(Block *b, u32int addr, int type, u32int tag, int recurse)
{
BList *p, **pp, bl;
/* remove bb from prior list */
for(pp=&b->prior; (p=*pp)!=nil; ){
if(p->part == PartData && p->addr == addr){
*pp = p->next;
blistFree(b->c, p);
}else
pp = &p->next;
}
bl.part = PartData;
bl.addr = addr;
bl.type = type;
bl.tag = tag;
if(b->l.epoch == 0)
assert(b->part == PartSuper);
bl.epoch = b->l.epoch;
bl.next = nil;
bl.recurse = recurse;
if(b->part == PartSuper && b->iostate == BioClean)
p = nil;
else
p = blistAlloc(b);
if(p == nil){
/*
* b has already been written to disk.
*/
doRemoveLink(b->c, &bl);
return;
}
/* Uhead is only processed when the block goes from Dirty -> Clean */
assert(b->iostate == BioDirty);
*p = bl;
if(b->uhead == nil)
b->uhead = p;
else
b->utail->next = p;
b->utail = p;
}
/*
* Process removal of a single block and perhaps its children.
*/
static void
doRemoveLink(Cache *c, BList *p)
{
int i, n, recurse;
u32int a;
Block *b;
Label l;
BList bl;
recurse = (p->recurse && p->type != BtData && p->type != BtDir);
/*
* We're not really going to overwrite b, but if we're not
* going to look at its contents, there is no point in reading
* them from the disk.
*/
b = cacheLocalData(c, p->addr, p->type, p->tag, recurse ? OReadOnly : OOverWrite, 0);
if(b == nil)
return;
/*
* When we're unlinking from the superblock, close with the next epoch.
*/
if(p->epoch == 0)
p->epoch = b->l.epoch+1;
/* sanity check */
if(b->l.epoch > p->epoch){
fprint(2, "%s: doRemoveLink: strange epoch %ud > %ud\n",
argv0, b->l.epoch, p->epoch);
blockPut(b);
return;
}
if(recurse){
n = c->size / VtScoreSize;
for(i=0; i<n; i++){
a = globalToLocal(b->data + i*VtScoreSize);
if(a == NilBlock || !readLabel(c, &l, a))
continue;
if(l.state&BsClosed)
continue;
/*
* If stack space becomes an issue...
p->addr = a;
p->type = l.type;
p->tag = l.tag;
doRemoveLink(c, p);
*/
bl.part = PartData;
bl.addr = a;
bl.type = l.type;
bl.tag = l.tag;
bl.epoch = p->epoch;
bl.next = nil;
bl.recurse = 1;
/* give up the block lock - share with others */
blockPut(b);
doRemoveLink(c, &bl);
b = cacheLocalData(c, p->addr, p->type, p->tag, OReadOnly, 0);
if(b == nil){
fprint(2, "%s: warning: lost block in doRemoveLink\n",
argv0);
return;
}
}
}
l = b->l;
l.state |= BsClosed;
l.epochClose = p->epoch;
if(l.epochClose == l.epoch){
/* lock ordering: trying for c->fl->lk while holding b->lk can deadlock */
if(!canqlock(&c->fl->lk)){
blockPut(b);
qlock(&c->fl->lk);
b = cacheLocalData(c, p->addr, p->type, p->tag, OOverWrite, 0);
if(b == nil){
fprint(2, "%s: warning: lost block at end of doRemoveLink\n",
argv0);
qunlock(&c->fl->lk);
return;
}
}
if(l.epoch == c->fl->epochLow)
c->fl->nused--;
blockSetLabel(b, &l, 0);
qunlock(&c->fl->lk);
}else
blockSetLabel(b, &l, 0);
blockPut(b);
}
/*
* Allocate a BList so that we can record a dependency
* or queue a removal related to block b.
* If we can't find a BList, we write out b and return nil.
*/
static BList *
blistAlloc(Block *b)
{
Cache *c;
BList *p;
if(b->iostate != BioDirty){
/*
* should not happen anymore -
* blockDirty used to flush but no longer does.
*/
assert(b->iostate == BioClean);
fprint(2, "%s: blistAlloc: called on clean block\n", argv0);
return nil;
}
c = b->c;
qlock(&c->lk);
if(c->blfree == nil){
/*
* No free BLists. What are our options?
*/
/* Block has no priors? Just write it. */
if(b->prior == nil){
qunlock(&c->lk);
diskWriteAndWait(c->disk, b);
return nil;
}
/*
* Wake the flush thread, which will hopefully free up
* some BLists for us. We used to flush a block from
* our own prior list and reclaim that BList, but this is
* a no-no: some of the blocks on our prior list may
* be locked by our caller. Or maybe their label blocks
* are locked by our caller. In any event, it's too hard
* to make sure we can do I/O for ourselves. Instead,
* we assume the flush thread will find something.
* (The flush thread never blocks waiting for a block,
* so it can't deadlock like we can.)
*/
while(c->blfree == nil){
rwakeup(&c->flush);
rsleep(&c->blrend);
if(c->blfree == nil)
fprint(2, "%s: flushing for blists\n", argv0);
}
}
p = c->blfree;
c->blfree = p->next;
qunlock(&c->lk);
return p;
}
static void
blistFree(Cache *c, BList *bl)
{
qlock(&c->lk);
bl->next = c->blfree;
c->blfree = bl;
rwakeup(&c->blrend);
qunlock(&c->lk);
}
char*
bsStr(int state)
{
static char s[100];
if(state == BsFree)
return "Free";
if(state == BsBad)
return "Bad";
sprint(s, "%x", state);
if(!(state&BsAlloc))
strcat(s, ",Free"); /* should not happen */
if(state&BsCopied)
strcat(s, ",Copied");
if(state&BsVenti)
strcat(s, ",Venti");
if(state&BsClosed)
strcat(s, ",Closed");
return s;
}
char *
bioStr(int iostate)
{
switch(iostate){
default:
return "Unknown!!";
case BioEmpty:
return "Empty";
case BioLabel:
return "Label";
case BioClean:
return "Clean";
case BioDirty:
return "Dirty";
case BioReading:
return "Reading";
case BioWriting:
return "Writing";
case BioReadError:
return "ReadError";
case BioVentiError:
return "VentiError";
case BioMax:
return "Max";
}
}
static char *bttab[] = {
"BtData",
"BtData+1",
"BtData+2",
"BtData+3",
"BtData+4",
"BtData+5",
"BtData+6",
"BtData+7",
"BtDir",
"BtDir+1",
"BtDir+2",
"BtDir+3",
"BtDir+4",
"BtDir+5",
"BtDir+6",
"BtDir+7",
};
char*
btStr(int type)
{
if(type < nelem(bttab))
return bttab[type];
return "unknown";
}
int
labelFmt(Fmt *f)
{
Label *l;
l = va_arg(f->args, Label*);
return fmtprint(f, "%s,%s,e=%ud,%d,tag=%#ux",
btStr(l->type), bsStr(l->state), l->epoch, (int)l->epochClose, l->tag);
}
int
scoreFmt(Fmt *f)
{
uchar *v;
int i;
u32int addr;
v = va_arg(f->args, uchar*);
if(v == nil){
fmtprint(f, "*");
}else if((addr = globalToLocal(v)) != NilBlock)
fmtprint(f, "0x%.8ux", addr);
else{
for(i = 0; i < VtScoreSize; i++)
fmtprint(f, "%2.2ux", v[i]);
}
return 0;
}
static int
upHeap(int i, Block *b)
{
Block *bb;
u32int now;
int p;
Cache *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, Block *b)
{
Block *bb;
u32int now;
int k;
Cache *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(Block *b)
{
int i, si;
Cache *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(Block *b)
{
assert(b->heap == BadHeap);
upHeap(b->c->nheap++, b);
rwakeup(&b->c->heapwait);
}
/*
* Get just the label for a block.
*/
int
readLabel(Cache *c, Label *l, u32int addr)
{
int lpb;
Block *b;
u32int a;
lpb = c->size / LabelSize;
a = addr / lpb;
b = cacheLocal(c, PartLabel, a, OReadOnly);
if(b == nil){
blockPut(b);
return 0;
}
if(!labelUnpack(l, b->data, addr%lpb)){
blockPut(b);
return 0;
}
blockPut(b);
return 1;
}
/*
* Process unlink queue.
* Called with c->lk held.
*/
static void
unlinkBody(Cache *c)
{
BList *p;
while(c->uhead != nil){
p = c->uhead;
c->uhead = p->next;
qunlock(&c->lk);
doRemoveLink(c, p);
qlock(&c->lk);
p->next = c->blfree;
c->blfree = p;
}
}
/*
* Occasionally unlink the blocks on the cache unlink queue.
*/
static void
unlinkThread(void *a)
{
Cache *c = a;
threadsetname("unlink");
qlock(&c->lk);
for(;;){
while(c->uhead == nil && c->die.l == nil)
rsleep(&c->unlink);
if(c->die.l != nil)
break;
unlinkBody(c);
}
c->ref--;
rwakeup(&c->die);
qunlock(&c->lk);
}
static int
baddrCmp(void *a0, void *a1)
{
BAddr *b0, *b1;
b0 = a0;
b1 = a1;
if(b0->part < b1->part)
return -1;
if(b0->part > b1->part)
return 1;
if(b0->addr < b1->addr)
return -1;
if(b0->addr > b1->addr)
return 1;
return 0;
}
/*
* Scan the block list for dirty blocks; add them to the list c->baddr.
*/
static void
flushFill(Cache *c)
{
int i, ndirty;
BAddr *p;
Block *b;
qlock(&c->lk);
if(c->ndirty == 0){
qunlock(&c->lk);
return;
}
p = c->baddr;
ndirty = 0;
for(i=0; i<c->nblocks; i++){
b = c->blocks + i;
if(b->part == PartError)
continue;
if(b->iostate == BioDirty || b->iostate == BioWriting)
ndirty++;
if(b->iostate != BioDirty)
continue;
p->part = b->part;
p->addr = b->addr;
p->vers = b->vers;
p++;
}
if(ndirty != c->ndirty){
fprint(2, "%s: ndirty mismatch expected %d found %d\n",
argv0, c->ndirty, ndirty);
c->ndirty = ndirty;
}
qunlock(&c->lk);
c->bw = p - c->baddr;
qsort(c->baddr, c->bw, sizeof(BAddr), baddrCmp);
}
/*
* This is not thread safe, i.e. it can't be called from multiple threads.
*
* It's okay how we use it, because it only gets called in
* the flushThread. And cacheFree, but only after
* cacheFree has killed off the flushThread.
*/
static int
cacheFlushBlock(Cache *c)
{
Block *b;
BAddr *p;
int lockfail, nfail;
nfail = 0;
for(;;){
if(c->br == c->be){
if(c->bw == 0 || c->bw == c->be)
flushFill(c);
c->br = 0;
c->be = c->bw;
c->bw = 0;
c->nflush = 0;
}
if(c->br == c->be)
return 0;
p = c->baddr + c->br;
c->br++;
b = _cacheLocalLookup(c, p->part, p->addr, p->vers, Nowaitlock,
&lockfail);
if(b && blockWrite(b, Nowaitlock)){
c->nflush++;
blockPut(b);
return 1;
}
if(b)
blockPut(b);
/*
* Why didn't we write the block?
*/
/* Block already written out */
if(b == nil && !lockfail)
continue;
/* Failed to acquire lock; sleep if happens a lot. */
if(lockfail && ++nfail > 100){
sleep(500);
nfail = 0;
}
/* Requeue block. */
if(c->bw < c->be)
c->baddr[c->bw++] = *p;
}
}
/*
* Occasionally flush dirty blocks from memory to the disk.
*/
static void
flushThread(void *a)
{
Cache *c = a;
int i;
threadsetname("flush");
qlock(&c->lk);
while(c->die.l == nil){
rsleep(&c->flush);
qunlock(&c->lk);
for(i=0; i<FlushSize; i++)
if(!cacheFlushBlock(c)){
/*
* If i==0, could be someone is waking us repeatedly
* to flush the cache but there's no work to do.
* Pause a little.
*/
if(i==0){
// fprint(2, "%s: flushthread found "
// "nothing to flush - %d dirty\n",
// argv0, c->ndirty);
sleep(250);
}
break;
}
if(i==0 && c->ndirty){
/*
* All the blocks are being written right now -- there's nothing to do.
* We might be spinning with cacheFlush though -- he'll just keep
* kicking us until c->ndirty goes down. Probably we should sleep
* on something that the diskThread can kick, but for now we'll
* just pause for a little while waiting for disks to finish.
*/
sleep(100);
}
qlock(&c->lk);
rwakeupall(&c->flushwait);
}
c->ref--;
rwakeup(&c->die);
qunlock(&c->lk);
}
/*
* Flush the cache.
*/
void
cacheFlush(Cache *c, int wait)
{
qlock(&c->lk);
if(wait){
while(c->ndirty){
// consPrint("cacheFlush: %d dirty blocks, uhead %p\n",
// c->ndirty, c->uhead);
rwakeup(&c->flush);
rsleep(&c->flushwait);
}
// consPrint("cacheFlush: done (uhead %p)\n", c->ndirty, c->uhead);
}else if(c->ndirty)
rwakeup(&c->flush);
qunlock(&c->lk);
}
/*
* Kick the flushThread every 30 seconds.
*/
static void
cacheSync(void *v)
{
Cache *c;
c = v;
cacheFlush(c, 0);
}