#include "redis.h"
#include <fcntl.h>
#include <pthread.h>
#include <math.h>
#include <signal.h>
/* Virtual Memory is composed mainly of two subsystems:
* - Blocking Virutal Memory
* - Threaded Virtual Memory I/O
* The two parts are not fully decoupled, but functions are split among two
* different sections of the source code (delimited by comments) in order to
* make more clear what functionality is about the blocking VM and what about
* the threaded (not blocking) VM.
*
* Redis VM design:
*
* Redis VM is a blocking VM (one that blocks reading swapped values from
* disk into memory when a value swapped out is needed in memory) that is made
* unblocking by trying to examine the command argument vector in order to
* load in background values that will likely be needed in order to exec
* the command. The command is executed only once all the relevant keys
* are loaded into memory.
*
* This basically is almost as simple of a blocking VM, but almost as parallel
* as a fully non-blocking VM.
*/
/* =================== Virtual Memory - Blocking Side ====================== */
/* Create a VM pointer object. This kind of objects are used in place of
* values in the key -> value hash table, for swapped out objects. */
vmpointer *createVmPointer(int vtype) {
vmpointer *vp = zmalloc(sizeof(vmpointer));
vp->type = REDIS_VMPOINTER;
vp->storage = REDIS_VM_SWAPPED;
vp->vtype = vtype;
return vp;
}
void vmInit(void) {
off_t totsize;
int pipefds[2];
size_t stacksize;
struct flock fl;
if (server.vm_max_threads != 0)
zmalloc_enable_thread_safeness(); /* we need thread safe zmalloc() */
redisLog(REDIS_NOTICE,"Using '%s' as swap file",server.vm_swap_file);
/* Try to open the old swap file, otherwise create it */
if ((server.vm_fp = fopen(server.vm_swap_file,"r+b")) == NULL) {
server.vm_fp = fopen(server.vm_swap_file,"w+b");
}
if (server.vm_fp == NULL) {
redisLog(REDIS_WARNING,
"Can't open the swap file: %s. Exiting.",
strerror(errno));
exit(1);
}
server.vm_fd = fileno(server.vm_fp);
/* Lock the swap file for writing, this is useful in order to avoid
* another instance to use the same swap file for a config error. */
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = fl.l_len = 0;
if (fcntl(server.vm_fd,F_SETLK,&fl) == -1) {
redisLog(REDIS_WARNING,
"Can't lock the swap file at '%s': %s. Make sure it is not used by another Redis instance.", server.vm_swap_file, strerror(errno));
exit(1);
}
/* Initialize */
server.vm_next_page = 0;
server.vm_near_pages = 0;
server.vm_stats_used_pages = 0;
server.vm_stats_swapped_objects = 0;
server.vm_stats_swapouts = 0;
server.vm_stats_swapins = 0;
totsize = server.vm_pages*server.vm_page_size;
redisLog(REDIS_NOTICE,"Allocating %lld bytes of swap file",totsize);
if (ftruncate(server.vm_fd,totsize) == -1) {
redisLog(REDIS_WARNING,"Can't ftruncate swap file: %s. Exiting.",
strerror(errno));
exit(1);
} else {
redisLog(REDIS_NOTICE,"Swap file allocated with success");
}
server.vm_bitmap = zmalloc((server.vm_pages+7)/8);
redisLog(REDIS_VERBOSE,"Allocated %lld bytes page table for %lld pages",
(long long) (server.vm_pages+7)/8, server.vm_pages);
memset(server.vm_bitmap,0,(server.vm_pages+7)/8);
/* Initialize threaded I/O (used by Virtual Memory) */
server.io_newjobs = listCreate();
server.io_processing = listCreate();
server.io_processed = listCreate();
server.io_ready_clients = listCreate();
pthread_mutex_init(&server.io_mutex,NULL);
pthread_mutex_init(&server.obj_freelist_mutex,NULL);
pthread_mutex_init(&server.io_swapfile_mutex,NULL);
server.io_active_threads = 0;
if (pipe(pipefds) == -1) {
redisLog(REDIS_WARNING,"Unable to intialized VM: pipe(2): %s. Exiting."
,strerror(errno));
exit(1);
}
server.io_ready_pipe_read = pipefds[0];
server.io_ready_pipe_write = pipefds[1];
redisAssert(anetNonBlock(NULL,server.io_ready_pipe_read) != ANET_ERR);
/* LZF requires a lot of stack */
pthread_attr_init(&server.io_threads_attr);
pthread_attr_getstacksize(&server.io_threads_attr, &stacksize);
while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
pthread_attr_setstacksize(&server.io_threads_attr, stacksize);
/* Listen for events in the threaded I/O pipe */
if (aeCreateFileEvent(server.el, server.io_ready_pipe_read, AE_READABLE,
vmThreadedIOCompletedJob, NULL) == AE_ERR)
oom("creating file event");
}
/* Mark the page as used */
void vmMarkPageUsed(off_t page) {
off_t byte = page/8;
int bit = page&7;
redisAssert(vmFreePage(page) == 1);
server.vm_bitmap[byte] |= 1<<bit;
}
/* Mark N contiguous pages as used, with 'page' being the first. */
void vmMarkPagesUsed(off_t page, off_t count) {
off_t j;
for (j = 0; j < count; j++)
vmMarkPageUsed(page+j);
server.vm_stats_used_pages += count;
redisLog(REDIS_DEBUG,"Mark USED pages: %lld pages at %lld\n",
(long long)count, (long long)page);
}
/* Mark the page as free */
void vmMarkPageFree(off_t page) {
off_t byte = page/8;
int bit = page&7;
redisAssert(vmFreePage(page) == 0);
server.vm_bitmap[byte] &= ~(1<<bit);
}
/* Mark N contiguous pages as free, with 'page' being the first. */
void vmMarkPagesFree(off_t page, off_t count) {
off_t j;
for (j = 0; j < count; j++)
vmMarkPageFree(page+j);
server.vm_stats_used_pages -= count;
redisLog(REDIS_DEBUG,"Mark FREE pages: %lld pages at %lld\n",
(long long)count, (long long)page);
}
/* Test if the page is free */
int vmFreePage(off_t page) {
off_t byte = page/8;
int bit = page&7;
return (server.vm_bitmap[byte] & (1<<bit)) == 0;
}
/* Find N contiguous free pages storing the first page of the cluster in *first.
* Returns REDIS_OK if it was able to find N contiguous pages, otherwise
* REDIS_ERR is returned.
*
* This function uses a simple algorithm: we try to allocate
* REDIS_VM_MAX_NEAR_PAGES sequentially, when we reach this limit we start
* again from the start of the swap file searching for free spaces.
*
* If it looks pretty clear that there are no free pages near our offset
* we try to find less populated places doing a forward jump of
* REDIS_VM_MAX_RANDOM_JUMP, then we start scanning again a few pages
* without hurry, and then we jump again and so forth...
*
* This function can be improved using a free list to avoid to guess
* too much, since we could collect data about freed pages.
*
* note: I implemented this function just after watching an episode of
* Battlestar Galactica, where the hybrid was continuing to say "JUMP!"
*/
int vmFindContiguousPages(off_t *first, off_t n) {
off_t base, offset = 0, since_jump = 0, numfree = 0;
if (server.vm_near_pages == REDIS_VM_MAX_NEAR_PAGES) {
server.vm_near_pages = 0;
server.vm_next_page = 0;
}
server.vm_near_pages++; /* Yet another try for pages near to the old ones */
base = server.vm_next_page;
while(offset < server.vm_pages) {
off_t this = base+offset;
/* If we overflow, restart from page zero */
if (this >= server.vm_pages) {
this -= server.vm_pages;
if (this == 0) {
/* Just overflowed, what we found on tail is no longer
* interesting, as it's no longer contiguous. */
numfree = 0;
}
}
if (vmFreePage(this)) {
/* This is a free page */
numfree++;
/* Already got N free pages? Return to the caller, with success */
if (numfree == n) {
*first = this-(n-1);
server.vm_next_page = this+1;
redisLog(REDIS_DEBUG, "FOUND CONTIGUOUS PAGES: %lld pages at %lld\n", (long long) n, (long long) *first);
return REDIS_OK;
}
} else {
/* The current one is not a free page */
numfree = 0;
}
/* Fast-forward if the current page is not free and we already
* searched enough near this place. */
since_jump++;
if (!numfree && since_jump >= REDIS_VM_MAX_RANDOM_JUMP/4) {
offset += random() % REDIS_VM_MAX_RANDOM_JUMP;
since_jump = 0;
/* Note that even if we rewind after the jump, we are don't need
* to make sure numfree is set to zero as we only jump *if* it
* is set to zero. */
} else {
/* Otherwise just check the next page */
offset++;
}
}
return REDIS_ERR;
}
/* Write the specified object at the specified page of the swap file */
int vmWriteObjectOnSwap(robj *o, off_t page) {
if (server.vm_enabled) pthread_mutex_lock(&server.io_swapfile_mutex);
if (fseeko(server.vm_fp,page*server.vm_page_size,SEEK_SET) == -1) {
if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
redisLog(REDIS_WARNING,
"Critical VM problem in vmWriteObjectOnSwap(): can't seek: %s",
strerror(errno));
return REDIS_ERR;
}
rdbSaveObject(server.vm_fp,o);
fflush(server.vm_fp);
if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
return REDIS_OK;
}
/* Transfers the 'val' object to disk. Store all the information
* a 'vmpointer' object containing all the information needed to load the
* object back later is returned.
*
* If we can't find enough contiguous empty pages to swap the object on disk
* NULL is returned. */
vmpointer *vmSwapObjectBlocking(robj *val) {
off_t pages = rdbSavedObjectPages(val,NULL);
off_t page;
vmpointer *vp;
redisAssert(val->storage == REDIS_VM_MEMORY);
redisAssert(val->refcount == 1);
if (vmFindContiguousPages(&page,pages) == REDIS_ERR) return NULL;
if (vmWriteObjectOnSwap(val,page) == REDIS_ERR) return NULL;
vp = createVmPointer(val->type);
vp->page = page;
vp->usedpages = pages;
decrRefCount(val); /* Deallocate the object from memory. */
vmMarkPagesUsed(page,pages);
redisLog(REDIS_DEBUG,"VM: object %p swapped out at %lld (%lld pages)",
(void*) val,
(unsigned long long) page, (unsigned long long) pages);
server.vm_stats_swapped_objects++;
server.vm_stats_swapouts++;
return vp;
}
robj *vmReadObjectFromSwap(off_t page, int type) {
robj *o;
if (server.vm_enabled) pthread_mutex_lock(&server.io_swapfile_mutex);
if (fseeko(server.vm_fp,page*server.vm_page_size,SEEK_SET) == -1) {
redisLog(REDIS_WARNING,
"Unrecoverable VM problem in vmReadObjectFromSwap(): can't seek: %s",
strerror(errno));
_exit(1);
}
o = rdbLoadObject(type,server.vm_fp);
if (o == NULL) {
redisLog(REDIS_WARNING, "Unrecoverable VM problem in vmReadObjectFromSwap(): can't load object from swap file: %s", strerror(errno));
_exit(1);
}
if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
return o;
}
/* Load the specified object from swap to memory.
* The newly allocated object is returned.
*
* If preview is true the unserialized object is returned to the caller but
* the pages are not marked as freed, nor the vp object is freed. */
robj *vmGenericLoadObject(vmpointer *vp, int preview) {
robj *val;
redisAssert(vp->type == REDIS_VMPOINTER &&
(vp->storage == REDIS_VM_SWAPPED || vp->storage == REDIS_VM_LOADING));
val = vmReadObjectFromSwap(vp->page,vp->vtype);
if (!preview) {
redisLog(REDIS_DEBUG, "VM: object %p loaded from disk", (void*)vp);
vmMarkPagesFree(vp->page,vp->usedpages);
zfree(vp);
server.vm_stats_swapped_objects--;
} else {
redisLog(REDIS_DEBUG, "VM: object %p previewed from disk", (void*)vp);
}
server.vm_stats_swapins++;
return val;
}
/* Plain object loading, from swap to memory.
*
* 'o' is actually a redisVmPointer structure that will be freed by the call.
* The return value is the loaded object. */
robj *vmLoadObject(robj *o) {
/* If we are loading the object in background, stop it, we
* need to load this object synchronously ASAP. */
if (o->storage == REDIS_VM_LOADING)
vmCancelThreadedIOJob(o);
return vmGenericLoadObject((vmpointer*)o,0);
}
/* Just load the value on disk, without to modify the key.
* This is useful when we want to perform some operation on the value
* without to really bring it from swap to memory, like while saving the
* dataset or rewriting the append only log. */
robj *vmPreviewObject(robj *o) {
return vmGenericLoadObject((vmpointer*)o,1);
}
/* How a good candidate is this object for swapping?
* The better candidate it is, the greater the returned value.
*
* Currently we try to perform a fast estimation of the object size in
* memory, and combine it with aging informations.
*
* Basically swappability = idle-time * log(estimated size)
*
* Bigger objects are preferred over smaller objects, but not
* proportionally, this is why we use the logarithm. This algorithm is
* just a first try and will probably be tuned later. */
double computeObjectSwappability(robj *o) {
/* actual age can be >= minage, but not < minage. As we use wrapping
* 21 bit clocks with minutes resolution for the LRU. */
time_t minage = abs(server.lruclock - o->lru);
long asize = 0, elesize;
robj *ele;
list *l;
listNode *ln;
dict *d;
struct dictEntry *de;
int z;
if (minage <= 0) return 0;
switch(o->type) {
case REDIS_STRING:
if (o->encoding != REDIS_ENCODING_RAW) {
asize = sizeof(*o);
} else {
asize = sdslen(o->ptr)+sizeof(*o)+sizeof(long)*2;
}
break;
case REDIS_LIST:
if (o->encoding == REDIS_ENCODING_ZIPLIST) {
asize = sizeof(*o)+ziplistSize(o->ptr);
} else {
l = o->ptr;
ln = listFirst(l);
asize = sizeof(list);
if (ln) {
ele = ln->value;
elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
(sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
asize += (sizeof(listNode)+elesize)*listLength(l);
}
}
break;
case REDIS_SET:
case REDIS_ZSET:
z = (o->type == REDIS_ZSET);
d = z ? ((zset*)o->ptr)->dict : o->ptr;
asize = sizeof(dict)+(sizeof(struct dictEntry*)*dictSlots(d));
if (z) asize += sizeof(zset)-sizeof(dict);
if (dictSize(d)) {
de = dictGetRandomKey(d);
ele = dictGetEntryKey(de);
elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
(sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
asize += (sizeof(struct dictEntry)+elesize)*dictSize(d);
if (z) asize += sizeof(zskiplistNode)*dictSize(d);
}
break;
case REDIS_HASH:
if (o->encoding == REDIS_ENCODING_ZIPMAP) {
unsigned char *p = zipmapRewind((unsigned char*)o->ptr);
unsigned int len = zipmapLen((unsigned char*)o->ptr);
unsigned int klen, vlen;
unsigned char *key, *val;
if ((p = zipmapNext(p,&key,&klen,&val,&vlen)) == NULL) {
klen = 0;
vlen = 0;
}
asize = len*(klen+vlen+3);
} else if (o->encoding == REDIS_ENCODING_HT) {
d = o->ptr;
asize = sizeof(dict)+(sizeof(struct dictEntry*)*dictSlots(d));
if (dictSize(d)) {
de = dictGetRandomKey(d);
ele = dictGetEntryKey(de);
elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
(sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
ele = dictGetEntryVal(de);
elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
(sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
asize += (sizeof(struct dictEntry)+elesize)*dictSize(d);
}
}
break;
}
return (double)minage*log(1+asize);
}
/* Try to swap an object that's a good candidate for swapping.
* Returns REDIS_OK if the object was swapped, REDIS_ERR if it's not possible
* to swap any object at all.
*
* If 'usethreaded' is true, Redis will try to swap the object in background
* using I/O threads. */
int vmSwapOneObject(int usethreads) {
int j, i;
struct dictEntry *best = NULL;
double best_swappability = 0;
redisDb *best_db = NULL;
robj *val;
sds key;
for (j = 0; j < server.dbnum; j++) {
redisDb *db = server.db+j;
/* Why maxtries is set to 100?
* Because this way (usually) we'll find 1 object even if just 1% - 2%
* are swappable objects */
int maxtries = 100;
if (dictSize(db->dict) == 0) continue;
for (i = 0; i < 5; i++) {
dictEntry *de;
double swappability;
if (maxtries) maxtries--;
de = dictGetRandomKey(db->dict);
val = dictGetEntryVal(de);
/* Only swap objects that are currently in memory.
*
* Also don't swap shared objects: not a good idea in general and
* we need to ensure that the main thread does not touch the
* object while the I/O thread is using it, but we can't
* control other keys without adding additional mutex. */
if (val->storage != REDIS_VM_MEMORY || val->refcount != 1) {
if (maxtries) i--; /* don't count this try */
continue;
}
swappability = computeObjectSwappability(val);
if (!best || swappability > best_swappability) {
best = de;
best_swappability = swappability;
best_db = db;
}
}
}
if (best == NULL) return REDIS_ERR;
key = dictGetEntryKey(best);
val = dictGetEntryVal(best);
redisLog(REDIS_DEBUG,"Key with best swappability: %s, %f",
key, best_swappability);
/* Swap it */
if (usethreads) {
robj *keyobj = createStringObject(key,sdslen(key));
vmSwapObjectThreaded(keyobj,val,best_db);
decrRefCount(keyobj);
return REDIS_OK;
} else {
vmpointer *vp;
if ((vp = vmSwapObjectBlocking(val)) != NULL) {
dictGetEntryVal(best) = vp;
return REDIS_OK;
} else {
return REDIS_ERR;
}
}
}
int vmSwapOneObjectBlocking() {
return vmSwapOneObject(0);
}
int vmSwapOneObjectThreaded() {
return vmSwapOneObject(1);
}
/* Return true if it's safe to swap out objects in a given moment.
* Basically we don't want to swap objects out while there is a BGSAVE
* or a BGAEOREWRITE running in backgroud. */
int vmCanSwapOut(void) {
return (server.bgsavechildpid == -1 && server.bgrewritechildpid == -1);
}
/* =================== Virtual Memory - Threaded I/O ======================= */
void freeIOJob(iojob *j) {
if ((j->type == REDIS_IOJOB_PREPARE_SWAP ||
j->type == REDIS_IOJOB_DO_SWAP ||
j->type == REDIS_IOJOB_LOAD) && j->val != NULL)
{
/* we fix the storage type, otherwise decrRefCount() will try to
* kill the I/O thread Job (that does no longer exists). */
if (j->val->storage == REDIS_VM_SWAPPING)
j->val->storage = REDIS_VM_MEMORY;
decrRefCount(j->val);
}
decrRefCount(j->key);
zfree(j);
}
/* Every time a thread finished a Job, it writes a byte into the write side
* of an unix pipe in order to "awake" the main thread, and this function
* is called. */
void vmThreadedIOCompletedJob(aeEventLoop *el, int fd, void *privdata,
int mask)
{
char buf[1];
int retval, processed = 0, toprocess = -1, trytoswap = 1;
REDIS_NOTUSED(el);
REDIS_NOTUSED(mask);
REDIS_NOTUSED(privdata);
/* For every byte we read in the read side of the pipe, there is one
* I/O job completed to process. */
while((retval = read(fd,buf,1)) == 1) {
iojob *j;
listNode *ln;
struct dictEntry *de;
redisLog(REDIS_DEBUG,"Processing I/O completed job");
/* Get the processed element (the oldest one) */
lockThreadedIO();
redisAssert(listLength(server.io_processed) != 0);
if (toprocess == -1) {
toprocess = (listLength(server.io_processed)*REDIS_MAX_COMPLETED_JOBS_PROCESSED)/100;
if (toprocess <= 0) toprocess = 1;
}
ln = listFirst(server.io_processed);
j = ln->value;
listDelNode(server.io_processed,ln);
unlockThreadedIO();
/* If this job is marked as canceled, just ignore it */
if (j->canceled) {
freeIOJob(j);
continue;
}
/* Post process it in the main thread, as there are things we
* can do just here to avoid race conditions and/or invasive locks */
redisLog(REDIS_DEBUG,"COMPLETED Job type: %d, ID %p, key: %s", j->type, (void*)j->id, (unsigned char*)j->key->ptr);
de = dictFind(j->db->dict,j->key->ptr);
redisAssert(de != NULL);
if (j->type == REDIS_IOJOB_LOAD) {
redisDb *db;
vmpointer *vp = dictGetEntryVal(de);
/* Key loaded, bring it at home */
vmMarkPagesFree(vp->page,vp->usedpages);
redisLog(REDIS_DEBUG, "VM: object %s loaded from disk (threaded)",
(unsigned char*) j->key->ptr);
server.vm_stats_swapped_objects--;
server.vm_stats_swapins++;
dictGetEntryVal(de) = j->val;
incrRefCount(j->val);
db = j->db;
/* Handle clients waiting for this key to be loaded. */
handleClientsBlockedOnSwappedKey(db,j->key);
freeIOJob(j);
zfree(vp);
} else if (j->type == REDIS_IOJOB_PREPARE_SWAP) {
/* Now we know the amount of pages required to swap this object.
* Let's find some space for it, and queue this task again
* rebranded as REDIS_IOJOB_DO_SWAP. */
if (!vmCanSwapOut() ||
vmFindContiguousPages(&j->page,j->pages) == REDIS_ERR)
{
/* Ooops... no space or we can't swap as there is
* a fork()ed Redis trying to save stuff on disk. */
j->val->storage = REDIS_VM_MEMORY; /* undo operation */
freeIOJob(j);
} else {
/* Note that we need to mark this pages as used now,
* if the job will be canceled, we'll mark them as freed
* again. */
vmMarkPagesUsed(j->page,j->pages);
j->type = REDIS_IOJOB_DO_SWAP;
lockThreadedIO();
queueIOJob(j);
unlockThreadedIO();
}
} else if (j->type == REDIS_IOJOB_DO_SWAP) {
vmpointer *vp;
/* Key swapped. We can finally free some memory. */
if (j->val->storage != REDIS_VM_SWAPPING) {
vmpointer *vp = (vmpointer*) j->id;
printf("storage: %d\n",vp->storage);
printf("key->name: %s\n",(char*)j->key->ptr);
printf("val: %p\n",(void*)j->val);
printf("val->type: %d\n",j->val->type);
printf("val->ptr: %s\n",(char*)j->val->ptr);
}
redisAssert(j->val->storage == REDIS_VM_SWAPPING);
vp = createVmPointer(j->val->type);
vp->page = j->page;
vp->usedpages = j->pages;
dictGetEntryVal(de) = vp;
/* Fix the storage otherwise decrRefCount will attempt to
* remove the associated I/O job */
j->val->storage = REDIS_VM_MEMORY;
decrRefCount(j->val);
redisLog(REDIS_DEBUG,
"VM: object %s swapped out at %lld (%lld pages) (threaded)",
(unsigned char*) j->key->ptr,
(unsigned long long) j->page, (unsigned long long) j->pages);
server.vm_stats_swapped_objects++;
server.vm_stats_swapouts++;
freeIOJob(j);
/* Put a few more swap requests in queue if we are still
* out of memory */
if (trytoswap && vmCanSwapOut() &&
zmalloc_used_memory() > server.vm_max_memory)
{
int more = 1;
while(more) {
lockThreadedIO();
more = listLength(server.io_newjobs) <
(unsigned) server.vm_max_threads;
unlockThreadedIO();
/* Don't waste CPU time if swappable objects are rare. */
if (vmSwapOneObjectThreaded() == REDIS_ERR) {
trytoswap = 0;
break;
}
}
}
}
processed++;
if (processed == toprocess) return;
}
if (retval < 0 && errno != EAGAIN) {
redisLog(REDIS_WARNING,
"WARNING: read(2) error in vmThreadedIOCompletedJob() %s",
strerror(errno));
}
}
void lockThreadedIO(void) {
pthread_mutex_lock(&server.io_mutex);
}
void unlockThreadedIO(void) {
pthread_mutex_unlock(&server.io_mutex);
}
/* Remove the specified object from the threaded I/O queue if still not
* processed, otherwise make sure to flag it as canceled. */
void vmCancelThreadedIOJob(robj *o) {
list *lists[3] = {
server.io_newjobs, /* 0 */
server.io_processing, /* 1 */
server.io_processed /* 2 */
};
int i;
redisAssert(o->storage == REDIS_VM_LOADING || o->storage == REDIS_VM_SWAPPING);
again:
lockThreadedIO();
/* Search for a matching object in one of the queues */
for (i = 0; i < 3; i++) {
listNode *ln;
listIter li;
listRewind(lists[i],&li);
while ((ln = listNext(&li)) != NULL) {
iojob *job = ln->value;
if (job->canceled) continue; /* Skip this, already canceled. */
if (job->id == o) {
redisLog(REDIS_DEBUG,"*** CANCELED %p (key %s) (type %d) (LIST ID %d)\n",
(void*)job, (char*)job->key->ptr, job->type, i);
/* Mark the pages as free since the swap didn't happened
* or happened but is now discarded. */
if (i != 1 && job->type == REDIS_IOJOB_DO_SWAP)
vmMarkPagesFree(job->page,job->pages);
/* Cancel the job. It depends on the list the job is
* living in. */
switch(i) {
case 0: /* io_newjobs */
/* If the job was yet not processed the best thing to do
* is to remove it from the queue at all */
freeIOJob(job);
listDelNode(lists[i],ln);
break;
case 1: /* io_processing */
/* Oh Shi- the thread is messing with the Job:
*
* Probably it's accessing the object if this is a
* PREPARE_SWAP or DO_SWAP job.
* If it's a LOAD job it may be reading from disk and
* if we don't wait for the job to terminate before to
* cancel it, maybe in a few microseconds data can be
* corrupted in this pages. So the short story is:
*
* Better to wait for the job to move into the
* next queue (processed)... */
/* We try again and again until the job is completed. */
unlockThreadedIO();
/* But let's wait some time for the I/O thread
* to finish with this job. After all this condition
* should be very rare. */
usleep(1);
goto again;
case 2: /* io_processed */
/* The job was already processed, that's easy...
* just mark it as canceled so that we'll ignore it
* when processing completed jobs. */
job->canceled = 1;
break;
}
/* Finally we have to adjust the storage type of the object
* in order to "UNDO" the operaiton. */
if (o->storage == REDIS_VM_LOADING)
o->storage = REDIS_VM_SWAPPED;
else if (o->storage == REDIS_VM_SWAPPING)
o->storage = REDIS_VM_MEMORY;
unlockThreadedIO();
redisLog(REDIS_DEBUG,"*** DONE");
return;
}
}
}
unlockThreadedIO();
printf("Not found: %p\n", (void*)o);
redisAssert(1 != 1); /* We should never reach this */
}
void *IOThreadEntryPoint(void *arg) {
iojob *j;
listNode *ln;
REDIS_NOTUSED(arg);
pthread_detach(pthread_self());
while(1) {
/* Get a new job to process */
lockThreadedIO();
if (listLength(server.io_newjobs) == 0) {
/* No new jobs in queue, exit. */
redisLog(REDIS_DEBUG,"Thread %ld exiting, nothing to do",
(long) pthread_self());
server.io_active_threads--;
unlockThreadedIO();
return NULL;
}
ln = listFirst(server.io_newjobs);
j = ln->value;
listDelNode(server.io_newjobs,ln);
/* Add the job in the processing queue */
j->thread = pthread_self();
listAddNodeTail(server.io_processing,j);
ln = listLast(server.io_processing); /* We use ln later to remove it */
unlockThreadedIO();
redisLog(REDIS_DEBUG,"Thread %ld got a new job (type %d): %p about key '%s'",
(long) pthread_self(), j->type, (void*)j, (char*)j->key->ptr);
/* Process the Job */
if (j->type == REDIS_IOJOB_LOAD) {
vmpointer *vp = (vmpointer*)j->id;
j->val = vmReadObjectFromSwap(j->page,vp->vtype);
} else if (j->type == REDIS_IOJOB_PREPARE_SWAP) {
FILE *fp = fopen("/dev/null","w+");
j->pages = rdbSavedObjectPages(j->val,fp);
fclose(fp);
} else if (j->type == REDIS_IOJOB_DO_SWAP) {
if (vmWriteObjectOnSwap(j->val,j->page) == REDIS_ERR)
j->canceled = 1;
}
/* Done: insert the job into the processed queue */
redisLog(REDIS_DEBUG,"Thread %ld completed the job: %p (key %s)",
(long) pthread_self(), (void*)j, (char*)j->key->ptr);
lockThreadedIO();
listDelNode(server.io_processing,ln);
listAddNodeTail(server.io_processed,j);
unlockThreadedIO();
/* Signal the main thread there is new stuff to process */
redisAssert(write(server.io_ready_pipe_write,"x",1) == 1);
}
return NULL; /* never reached */
}
void spawnIOThread(void) {
pthread_t thread;
sigset_t mask, omask;
int err;
sigemptyset(&mask);
sigaddset(&mask,SIGCHLD);
sigaddset(&mask,SIGHUP);
sigaddset(&mask,SIGPIPE);
pthread_sigmask(SIG_SETMASK, &mask, &omask);
while ((err = pthread_create(&thread,&server.io_threads_attr,IOThreadEntryPoint,NULL)) != 0) {
redisLog(REDIS_WARNING,"Unable to spawn an I/O thread: %s",
strerror(err));
usleep(1000000);
}
pthread_sigmask(SIG_SETMASK, &omask, NULL);
server.io_active_threads++;
}
/* We need to wait for the last thread to exit before we are able to
* fork() in order to BGSAVE or BGREWRITEAOF. */
void waitEmptyIOJobsQueue(void) {
while(1) {
int io_processed_len;
lockThreadedIO();
if (listLength(server.io_newjobs) == 0 &&
listLength(server.io_processing) == 0 &&
server.io_active_threads == 0)
{
unlockThreadedIO();
return;
}
/* While waiting for empty jobs queue condition we post-process some
* finshed job, as I/O threads may be hanging trying to write against
* the io_ready_pipe_write FD but there are so much pending jobs that
* it's blocking. */
io_processed_len = listLength(server.io_processed);
unlockThreadedIO();
if (io_processed_len) {
vmThreadedIOCompletedJob(NULL,server.io_ready_pipe_read,NULL,0);
usleep(1000); /* 1 millisecond */
} else {
usleep(10000); /* 10 milliseconds */
}
}
}
void vmReopenSwapFile(void) {
/* Note: we don't close the old one as we are in the child process
* and don't want to mess at all with the original file object. */
server.vm_fp = fopen(server.vm_swap_file,"r+b");
if (server.vm_fp == NULL) {
redisLog(REDIS_WARNING,"Can't re-open the VM swap file: %s. Exiting.",
server.vm_swap_file);
_exit(1);
}
server.vm_fd = fileno(server.vm_fp);
}
/* This function must be called while with threaded IO locked */
void queueIOJob(iojob *j) {
redisLog(REDIS_DEBUG,"Queued IO Job %p type %d about key '%s'\n",
(void*)j, j->type, (char*)j->key->ptr);
listAddNodeTail(server.io_newjobs,j);
if (server.io_active_threads < server.vm_max_threads)
spawnIOThread();
}
int vmSwapObjectThreaded(robj *key, robj *val, redisDb *db) {
iojob *j;
j = zmalloc(sizeof(*j));
j->type = REDIS_IOJOB_PREPARE_SWAP;
j->db = db;
j->key = key;
incrRefCount(key);
j->id = j->val = val;
incrRefCount(val);
j->canceled = 0;
j->thread = (pthread_t) -1;
val->storage = REDIS_VM_SWAPPING;
lockThreadedIO();
queueIOJob(j);
unlockThreadedIO();
return REDIS_OK;
}
/* ============ Virtual Memory - Blocking clients on missing keys =========== */
/* This function makes the clinet 'c' waiting for the key 'key' to be loaded.
* If there is not already a job loading the key, it is craeted.
* The key is added to the io_keys list in the client structure, and also
* in the hash table mapping swapped keys to waiting clients, that is,
* server.io_waited_keys. */
int waitForSwappedKey(redisClient *c, robj *key) {
struct dictEntry *de;
robj *o;
list *l;
/* If the key does not exist or is already in RAM we don't need to
* block the client at all. */
de = dictFind(c->db->dict,key->ptr);
if (de == NULL) return 0;
o = dictGetEntryVal(de);
if (o->storage == REDIS_VM_MEMORY) {
return 0;
} else if (o->storage == REDIS_VM_SWAPPING) {
/* We were swapping the key, undo it! */
vmCancelThreadedIOJob(o);
return 0;
}
/* OK: the key is either swapped, or being loaded just now. */
/* Add the key to the list of keys this client is waiting for.
* This maps clients to keys they are waiting for. */
listAddNodeTail(c->io_keys,key);
incrRefCount(key);
/* Add the client to the swapped keys => clients waiting map. */
de = dictFind(c->db->io_keys,key);
if (de == NULL) {
int retval;
/* For every key we take a list of clients blocked for it */
l = listCreate();
retval = dictAdd(c->db->io_keys,key,l);
incrRefCount(key);
redisAssert(retval == DICT_OK);
} else {
l = dictGetEntryVal(de);
}
listAddNodeTail(l,c);
/* Are we already loading the key from disk? If not create a job */
if (o->storage == REDIS_VM_SWAPPED) {
iojob *j;
vmpointer *vp = (vmpointer*)o;
o->storage = REDIS_VM_LOADING;
j = zmalloc(sizeof(*j));
j->type = REDIS_IOJOB_LOAD;
j->db = c->db;
j->id = (robj*)vp;
j->key = key;
incrRefCount(key);
j->page = vp->page;
j->val = NULL;
j->canceled = 0;
j->thread = (pthread_t) -1;
lockThreadedIO();
queueIOJob(j);
unlockThreadedIO();
}
return 1;
}
/* Preload keys for any command with first, last and step values for
* the command keys prototype, as defined in the command table. */
void waitForMultipleSwappedKeys(redisClient *c, struct redisCommand *cmd, int argc, robj **argv) {
int j, last;
if (cmd->vm_firstkey == 0) return;
last = cmd->vm_lastkey;
if (last < 0) last = argc+last;
for (j = cmd->vm_firstkey; j <= last; j += cmd->vm_keystep) {
redisAssert(j < argc);
waitForSwappedKey(c,argv[j]);
}
}
/* Preload keys needed for the ZUNIONSTORE and ZINTERSTORE commands.
* Note that the number of keys to preload is user-defined, so we need to
* apply a sanity check against argc. */
void zunionInterBlockClientOnSwappedKeys(redisClient *c, struct redisCommand *cmd, int argc, robj **argv) {
int i, num;
REDIS_NOTUSED(cmd);
num = atoi(argv[2]->ptr);
if (num > (argc-3)) return;
for (i = 0; i < num; i++) {
waitForSwappedKey(c,argv[3+i]);
}
}
/* Preload keys needed to execute the entire MULTI/EXEC block.
*
* This function is called by blockClientOnSwappedKeys when EXEC is issued,
* and will block the client when any command requires a swapped out value. */
void execBlockClientOnSwappedKeys(redisClient *c, struct redisCommand *cmd, int argc, robj **argv) {
int i, margc;
struct redisCommand *mcmd;
robj **margv;
REDIS_NOTUSED(cmd);
REDIS_NOTUSED(argc);
REDIS_NOTUSED(argv);
if (!(c->flags & REDIS_MULTI)) return;
for (i = 0; i < c->mstate.count; i++) {
mcmd = c->mstate.commands[i].cmd;
margc = c->mstate.commands[i].argc;
margv = c->mstate.commands[i].argv;
if (mcmd->vm_preload_proc != NULL) {
mcmd->vm_preload_proc(c,mcmd,margc,margv);
} else {
waitForMultipleSwappedKeys(c,mcmd,margc,margv);
}
}
}
/* Is this client attempting to run a command against swapped keys?
* If so, block it ASAP, load the keys in background, then resume it.
*
* The important idea about this function is that it can fail! If keys will
* still be swapped when the client is resumed, this key lookups will
* just block loading keys from disk. In practical terms this should only
* happen with SORT BY command or if there is a bug in this function.
*
* Return 1 if the client is marked as blocked, 0 if the client can
* continue as the keys it is going to access appear to be in memory. */
int blockClientOnSwappedKeys(redisClient *c, struct redisCommand *cmd) {
if (cmd->vm_preload_proc != NULL) {
cmd->vm_preload_proc(c,cmd,c->argc,c->argv);
} else {
waitForMultipleSwappedKeys(c,cmd,c->argc,c->argv);
}
/* If the client was blocked for at least one key, mark it as blocked. */
if (listLength(c->io_keys)) {
c->flags |= REDIS_IO_WAIT;
aeDeleteFileEvent(server.el,c->fd,AE_READABLE);
server.vm_blocked_clients++;
return 1;
} else {
return 0;
}
}
/* Remove the 'key' from the list of blocked keys for a given client.
*
* The function returns 1 when there are no longer blocking keys after
* the current one was removed (and the client can be unblocked). */
int dontWaitForSwappedKey(redisClient *c, robj *key) {
list *l;
listNode *ln;
listIter li;
struct dictEntry *de;
/* The key object might be destroyed when deleted from the c->io_keys
* list (and the "key" argument is physically the same object as the
* object inside the list), so we need to protect it. */
incrRefCount(key);
/* Remove the key from the list of keys this client is waiting for. */
listRewind(c->io_keys,&li);
while ((ln = listNext(&li)) != NULL) {
if (equalStringObjects(ln->value,key)) {
listDelNode(c->io_keys,ln);
break;
}
}
redisAssert(ln != NULL);
/* Remove the client form the key => waiting clients map. */
de = dictFind(c->db->io_keys,key);
redisAssert(de != NULL);
l = dictGetEntryVal(de);
ln = listSearchKey(l,c);
redisAssert(ln != NULL);
listDelNode(l,ln);
if (listLength(l) == 0)
dictDelete(c->db->io_keys,key);
decrRefCount(key);
return listLength(c->io_keys) == 0;
}
/* Every time we now a key was loaded back in memory, we handle clients
* waiting for this key if any. */
void handleClientsBlockedOnSwappedKey(redisDb *db, robj *key) {
struct dictEntry *de;
list *l;
listNode *ln;
int len;
de = dictFind(db->io_keys,key);
if (!de) return;
l = dictGetEntryVal(de);
len = listLength(l);
/* Note: we can't use something like while(listLength(l)) as the list
* can be freed by the calling function when we remove the last element. */
while (len--) {
ln = listFirst(l);
redisClient *c = ln->value;
if (dontWaitForSwappedKey(c,key)) {
/* Put the client in the list of clients ready to go as we
* loaded all the keys about it. */
listAddNodeTail(server.io_ready_clients,c);
}
}
}