+/* 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 ====================== */
+
+/* substitute the first occurrence of '%p' with the process pid in the
+ * swap file name. */
+static void expandVmSwapFilename(void) {
+ char *p = strstr(server.vm_swap_file,"%p");
+ sds new;
+
+ if (!p) return;
+ new = sdsempty();
+ *p = '\0';
+ new = sdscat(new,server.vm_swap_file);
+ new = sdscatprintf(new,"%ld",(long) getpid());
+ new = sdscat(new,p+2);
+ zfree(server.vm_swap_file);
+ server.vm_swap_file = new;
+}
+
+static void vmInit(void) {
+ off_t totsize;
+ int pipefds[2];
+ size_t stacksize;
+
+ if (server.vm_max_threads != 0)
+ zmalloc_enable_thread_safeness(); /* we need thread safe zmalloc() */
+
+ expandVmSwapFilename();
+ redisLog(REDIS_NOTICE,"Using '%s' as swap file",server.vm_swap_file);
+ 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,
+ "Impossible to open the swap file: %s. Exiting.",
+ strerror(errno));
+ exit(1);
+ }
+ server.vm_fd = fileno(server.vm_fp);
+ 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 */
+static 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. */
+static 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 */
+static 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. */
+static 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 */
+static 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!"
+ */
+static 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 */
+static 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;
+}
+
+/* Swap the 'val' object relative to 'key' into disk. Store all the information
+ * needed to later retrieve the object into the key object.
+ * If we can't find enough contiguous empty pages to swap the object on disk
+ * REDIS_ERR is returned. */
+static int vmSwapObjectBlocking(robj *key, robj *val) {
+ off_t pages = rdbSavedObjectPages(val,NULL);
+ off_t page;
+
+ assert(key->storage == REDIS_VM_MEMORY);
+ assert(key->refcount == 1);
+ if (vmFindContiguousPages(&page,pages) == REDIS_ERR) return REDIS_ERR;
+ if (vmWriteObjectOnSwap(val,page) == REDIS_ERR) return REDIS_ERR;
+ key->vm.page = page;
+ key->vm.usedpages = pages;
+ key->storage = REDIS_VM_SWAPPED;
+ key->vtype = val->type;
+ decrRefCount(val); /* Deallocate the object from memory. */
+ vmMarkPagesUsed(page,pages);
+ redisLog(REDIS_DEBUG,"VM: object %s swapped out at %lld (%lld pages)",
+ (unsigned char*) key->ptr,
+ (unsigned long long) page, (unsigned long long) pages);
+ server.vm_stats_swapped_objects++;
+ server.vm_stats_swapouts++;
+ return REDIS_OK;
+}
+
+static 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 value object relative to the 'key' object from swap to memory.
+ * The newly allocated object is returned.
+ *
+ * If preview is true the unserialized object is returned to the caller but
+ * no changes are made to the key object, nor the pages are marked as freed */
+static robj *vmGenericLoadObject(robj *key, int preview) {
+ robj *val;
+
+ redisAssert(key->storage == REDIS_VM_SWAPPED || key->storage == REDIS_VM_LOADING);
+ val = vmReadObjectFromSwap(key->vm.page,key->vtype);
+ if (!preview) {
+ key->storage = REDIS_VM_MEMORY;
+ key->vm.atime = server.unixtime;
+ vmMarkPagesFree(key->vm.page,key->vm.usedpages);
+ redisLog(REDIS_DEBUG, "VM: object %s loaded from disk",
+ (unsigned char*) key->ptr);
+ server.vm_stats_swapped_objects--;
+ } else {
+ redisLog(REDIS_DEBUG, "VM: object %s previewed from disk",
+ (unsigned char*) key->ptr);
+ }
+ server.vm_stats_swapins++;
+ return val;
+}
+
+/* Plain object loading, from swap to memory */
+static robj *vmLoadObject(robj *key) {
+ /* If we are loading the object in background, stop it, we
+ * need to load this object synchronously ASAP. */
+ if (key->storage == REDIS_VM_LOADING)
+ vmCancelThreadedIOJob(key);
+ return vmGenericLoadObject(key,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. */
+static robj *vmPreviewObject(robj *key) {
+ return vmGenericLoadObject(key,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. */
+static double computeObjectSwappability(robj *o) {
+ time_t age = server.unixtime - o->vm.atime;
+ long asize = 0;
+ list *l;
+ dict *d;
+ struct dictEntry *de;
+ int z;
+
+ if (age <= 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:
+ l = o->ptr;
+ listNode *ln = listFirst(l);
+
+ asize = sizeof(list);
+ if (ln) {
+ robj *ele = ln->value;
+ long elesize;
+
+ 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)) {
+ long elesize;
+ robj *ele;
+
+ 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;
+ }
+ return (double)age*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. */
+static int vmSwapOneObject(int usethreads) {
+ int j, i;
+ struct dictEntry *best = NULL;
+ double best_swappability = 0;
+ redisDb *best_db = NULL;
+ robj *key, *val;
+
+ 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);
+ key = dictGetEntryKey(de);
+ val = dictGetEntryVal(de);
+ /* Only swap objects that are currently in memory.
+ *
+ * Also don't swap shared objects if threaded VM is on, as we
+ * try 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 (key->storage != REDIS_VM_MEMORY ||
+ (server.vm_max_threads != 0 && 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->ptr, best_swappability);
+
+ /* Unshare the key if needed */
+ if (key->refcount > 1) {
+ robj *newkey = dupStringObject(key);
+ decrRefCount(key);
+ key = dictGetEntryKey(best) = newkey;
+ }
+ /* Swap it */
+ if (usethreads) {
+ vmSwapObjectThreaded(key,val,best_db);
+ return REDIS_OK;
+ } else {
+ if (vmSwapObjectBlocking(key,val) == REDIS_OK) {
+ dictGetEntryVal(best) = NULL;
+ return REDIS_OK;
+ } else {
+ return REDIS_ERR;
+ }
+ }
+}
+
+static int vmSwapOneObjectBlocking() {
+ return vmSwapOneObject(0);
+}
+
+static 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. */
+static int vmCanSwapOut(void) {
+ return (server.bgsavechildpid == -1 && server.bgrewritechildpid == -1);
+}
+
+/* Delete a key if swapped. Returns 1 if the key was found, was swapped
+ * and was deleted. Otherwise 0 is returned. */
+static int deleteIfSwapped(redisDb *db, robj *key) {
+ dictEntry *de;
+ robj *foundkey;
+
+ if ((de = dictFind(db->dict,key)) == NULL) return 0;
+ foundkey = dictGetEntryKey(de);
+ if (foundkey->storage == REDIS_VM_MEMORY) return 0;
+ deleteKey(db,key);
+ return 1;
+}
+
+/* =================== Virtual Memory - Threaded I/O ======================= */
+
+static 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)
+ 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. */
+static 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;
+ robj *key;
+ struct dictEntry *de;
+
+ redisLog(REDIS_DEBUG,"Processing I/O completed job");
+
+ /* Get the processed element (the oldest one) */
+ lockThreadedIO();
+ assert(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,"Job %p type: %d, key at %p (%s) refcount: %d\n", (void*) j, j->type, (void*)j->key, (char*)j->key->ptr, j->key->refcount);
+ de = dictFind(j->db->dict,j->key);
+ assert(de != NULL);
+ key = dictGetEntryKey(de);
+ if (j->type == REDIS_IOJOB_LOAD) {
+ redisDb *db;
+
+ /* Key loaded, bring it at home */
+ key->storage = REDIS_VM_MEMORY;
+ key->vm.atime = server.unixtime;
+ vmMarkPagesFree(key->vm.page,key->vm.usedpages);
+ redisLog(REDIS_DEBUG, "VM: object %s loaded from disk (threaded)",
+ (unsigned char*) key->ptr);
+ server.vm_stats_swapped_objects--;
+ server.vm_stats_swapins++;
+ dictGetEntryVal(de) = j->val;
+ incrRefCount(j->val);
+ db = j->db;
+ freeIOJob(j);
+ /* Handle clients waiting for this key to be loaded. */
+ handleClientsBlockedOnSwappedKey(db,key);
+ } 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. */
+ freeIOJob(j);
+ key->storage = REDIS_VM_MEMORY; /* undo operation */
+ } 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) {
+ robj *val;
+
+ /* Key swapped. We can finally free some memory. */
+ if (key->storage != REDIS_VM_SWAPPING) {
+ printf("key->storage: %d\n",key->storage);
+ printf("key->name: %s\n",(char*)key->ptr);
+ printf("key->refcount: %d\n",key->refcount);
+ 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(key->storage == REDIS_VM_SWAPPING);
+ val = dictGetEntryVal(de);
+ key->vm.page = j->page;
+ key->vm.usedpages = j->pages;
+ key->storage = REDIS_VM_SWAPPED;
+ key->vtype = j->val->type;
+ decrRefCount(val); /* Deallocate the object from memory. */
+ dictGetEntryVal(de) = NULL;
+ redisLog(REDIS_DEBUG,
+ "VM: object %s swapped out at %lld (%lld pages) (threaded)",
+ (unsigned char*) 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));
+ }
+}
+
+static void lockThreadedIO(void) {
+ pthread_mutex_lock(&server.io_mutex);
+}
+
+static 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. */
+static void vmCancelThreadedIOJob(robj *o) {
+ list *lists[3] = {
+ server.io_newjobs, /* 0 */
+ server.io_processing, /* 1 */
+ server.io_processed /* 2 */
+ };
+ int i;
+
+ assert(o->storage == REDIS_VM_LOADING || o->storage == REDIS_VM_SWAPPING);
+again:
+ lockThreadedIO();
+ /* Search for a matching key 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 (compareStringObjects(job->key,o) == 0) {
+ redisLog(REDIS_DEBUG,"*** CANCELED %p (%s) (type %d) (LIST ID %d)\n",
+ (void*)job, (char*)o->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();
+ return;
+ }
+ }
+ }
+ unlockThreadedIO();
+ assert(1 != 1); /* We should never reach this */
+}
+
+static 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) {
+ j->val = vmReadObjectFromSwap(j->page,j->key->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 */
+ assert(write(server.io_ready_pipe_write,"x",1) == 1);
+ }
+ return NULL; /* never reached */
+}
+
+static void spawnIOThread(void) {
+ pthread_t thread;
+ sigset_t mask, omask;
+
+ sigemptyset(&mask);
+ sigaddset(&mask,SIGCHLD);
+ sigaddset(&mask,SIGHUP);
+ sigaddset(&mask,SIGPIPE);
+ pthread_sigmask(SIG_SETMASK, &mask, &omask);
+ pthread_create(&thread,&server.io_threads_attr,IOThreadEntryPoint,NULL);
+ 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. */
+static 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 */
+ }
+ }
+}
+
+static 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 */
+static 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();
+}
+
+static int vmSwapObjectThreaded(robj *key, robj *val, redisDb *db) {
+ iojob *j;
+
+ assert(key->storage == REDIS_VM_MEMORY);
+ assert(key->refcount == 1);
+
+ j = zmalloc(sizeof(*j));
+ j->type = REDIS_IOJOB_PREPARE_SWAP;
+ j->db = db;
+ j->key = dupStringObject(key);
+ j->val = val;
+ incrRefCount(val);
+ j->canceled = 0;
+ j->thread = (pthread_t) -1;
+ key->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. */
+static 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);
+ if (de == NULL) return 0;
+ o = dictGetEntryKey(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);
+ assert(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;
+
+ o->storage = REDIS_VM_LOADING;
+ j = zmalloc(sizeof(*j));
+ j->type = REDIS_IOJOB_LOAD;
+ j->db = c->db;
+ j->key = dupStringObject(key);
+ j->key->vtype = o->vtype;
+ j->page = o->vm.page;
+ j->val = NULL;
+ j->canceled = 0;
+ j->thread = (pthread_t) -1;
+ lockThreadedIO();
+ queueIOJob(j);
+ unlockThreadedIO();
+ }
+ return 1;
+}
+
+/* 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. */
+static int blockClientOnSwappedKeys(struct redisCommand *cmd, redisClient *c) {
+ int j, last;
+
+ if (cmd->vm_firstkey == 0) return 0;
+ last = cmd->vm_lastkey;
+ if (last < 0) last = c->argc+last;
+ for (j = cmd->vm_firstkey; j <= last; j += cmd->vm_keystep)
+ waitForSwappedKey(c,c->argv[j]);
+ /* 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). */
+static int dontWaitForSwappedKey(redisClient *c, robj *key) {
+ list *l;
+ listNode *ln;
+ listIter li;
+ struct dictEntry *de;
+
+ /* Remove the key from the list of keys this client is waiting for. */
+ listRewind(c->io_keys,&li);
+ while ((ln = listNext(&li)) != NULL) {
+ if (compareStringObjects(ln->value,key) == 0) {
+ listDelNode(c->io_keys,ln);
+ break;
+ }
+ }
+ assert(ln != NULL);
+
+ /* Remove the client form the key => waiting clients map. */
+ de = dictFind(c->db->io_keys,key);
+ assert(de != NULL);
+ l = dictGetEntryVal(de);
+ ln = listSearchKey(l,c);
+ assert(ln != NULL);
+ listDelNode(l,ln);
+ if (listLength(l) == 0)
+ dictDelete(c->db->io_keys,key);
+
+ return listLength(c->io_keys) == 0;
+}
+
+static 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);
+ }
+ }
+}
+
projects / redis.git / blobdiff