这里主要是generic分配，功能比较直白。

/* Defrag helper for generic allocations.
 *
 * returns NULL in case the allocation wasn't moved.
 * when it returns a non-null value, the old pointer was already released
 * and should NOT be accessed. */
void* activeDefragAlloc(void *ptr) {
    size_t size;
    void *newptr;
    if(!je_get_defrag_hint(ptr)) {
        server.stat_active_defrag_misses++;
        return NULL;
    }
    /* move this allocation to a new allocation.
     * make sure not to use the thread cache. so that we don't get back the same
     * pointers we try to free */
    size = zmalloc_size(ptr);
    newptr = zmalloc_no_tcache(size);
    memcpy(newptr, ptr, size);
    zfree_no_tcache(ptr);
    return newptr;
}

/*Defrag helper for sds strings
 *
 * returns NULL in case the allocation wasn't moved.
 * when it returns a non-null value, the old pointer was already released
 * and should NOT be accessed. */
sds activeDefragSds(sds sdsptr) {
    void* ptr = sdsAllocPtr(sdsptr);
    void* newptr = activeDefragAlloc(ptr);
    if (newptr) {
        size_t offset = sdsptr - (char*)ptr;
        sdsptr = (char*)newptr + offset;
        return sdsptr;
    }
    return NULL;
}

/* Defrag helper for robj and/or string objects
 *
 * returns NULL in case the allocation wasn't moved.
 * when it returns a non-null value, the old pointer was already released
 * and should NOT be accessed. */
robj *activeDefragStringOb(robj* ob, long *defragged) {
    robj *ret = NULL;
    if (ob->refcount!=1)
        return NULL;

    /* try to defrag robj (only if not an EMBSTR type (handled below). */
    if (ob->type!=OBJ_STRING || ob->encoding!=OBJ_ENCODING_EMBSTR) {
        if ((ret = activeDefragAlloc(ob))) {
            ob = ret;
            (*defragged)++;
        }
    }

    /* try to defrag string object */
    if (ob->type == OBJ_STRING) {
        if(ob->encoding==OBJ_ENCODING_RAW) {
            sds newsds = activeDefragSds((sds)ob->ptr);
            if (newsds) {
                ob->ptr = newsds;
                (*defragged)++;
            }
        } else if (ob->encoding==OBJ_ENCODING_EMBSTR) {
            /* The sds is embedded in the object allocation, calculate the
             * offset and update the pointer in the new allocation. */
            long ofs = (intptr_t)ob->ptr - (intptr_t)ob;
            if ((ret = activeDefragAlloc(ob))) {
                ret->ptr = (void*)((intptr_t)ret + ofs);
                (*defragged)++;
            }
        } else if (ob->encoding!=OBJ_ENCODING_INT) {
            serverPanic("Unknown string encoding");
        }
    }
    return ret;
}

/* Defrag helper for dictEntries to be used during dict iteration (called on
 * each step). Returns a stat of how many pointers were moved. */
long dictIterDefragEntry(dictIterator *iter) {
    /* This function is a little bit dirty since it messes with the internals
     * of the dict and it's iterator, but the benefit is that it is very easy
     * to use, and require no other changes in the dict. */
    long defragged = 0;
    dictht *ht;
    /* Handle the next entry (if there is one), and update the pointer in the
     * current entry. */
    if (iter->nextEntry) {
        dictEntry *newde = activeDefragAlloc(iter->nextEntry);
        if (newde) {
            defragged++;
            iter->nextEntry = newde;
            iter->entry->next = newde;
        }
    }
    /* handle the case of the first entry in the hash bucket. */
    ht = &iter->d->ht[iter->table];
    if (ht->table[iter->index] == iter->entry) {
        dictEntry *newde = activeDefragAlloc(iter->entry);
        if (newde) {
            iter->entry = newde;
            ht->table[iter->index] = newde;
            defragged++;
        }
    }
    return defragged;
}

/* Defrag helper for dict main allocations (dict struct, and hash tables).
 * receives a pointer to the dict* and implicitly updates it when the dict
 * struct itself was moved. Returns a stat of how many pointers were moved. */
long dictDefragTables(dict* d) {
    dictEntry **newtable;
    long defragged = 0;
    /* handle the first hash table */
    newtable = activeDefragAlloc(d->ht[0].table);
    if (newtable)
        defragged++, d->ht[0].table = newtable;
    /* handle the second hash table */
    if (d->ht[1].table) {
        newtable = activeDefragAlloc(d->ht[1].table);
        if (newtable)
            defragged++, d->ht[1].table = newtable;
    }
    return defragged;
}

/* Internal function used by zslDefrag */
void zslUpdateNode(zskiplist *zsl, zskiplistNode *oldnode, zskiplistNode *newnode, zskiplistNode **update) {
    int i;
    for (i = 0; i < zsl->level; i++) {
        if (update[i]->level[i].forward == oldnode)
            update[i]->level[i].forward = newnode;
    }
    serverAssert(zsl->header!=oldnode);
    if (newnode->level[0].forward) {
        serverAssert(newnode->level[0].forward->backward==oldnode);
        newnode->level[0].forward->backward = newnode;
    } else {
        serverAssert(zsl->tail==oldnode);
        zsl->tail = newnode;
    }
}

/* Defrag helper for sorted set.
 * Update the robj pointer, defrag the skiplist struct and return the new score
 * reference. We may not access oldele pointer (not even the pointer stored in
 * the skiplist), as it was already freed. Newele may be null, in which case we
 * only need to defrag the skiplist, but not update the obj pointer.
 * When return value is non-NULL, it is the score reference that must be updated
 * in the dict record. */
double *zslDefrag(zskiplist *zsl, double score, sds oldele, sds newele) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x, *newx;
    int i;
    sds ele = newele? newele: oldele;

    /* find the skiplist node referring to the object that was moved,
     * and all pointers that need to be updated if we'll end up moving the skiplist node. */
    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward &&
            x->level[i].forward->ele != oldele && /* make sure not to access the
                                                     ->obj pointer if it matches
                                                     oldele */
            (x->level[i].forward->score < score ||
                (x->level[i].forward->score == score &&
                sdscmp(x->level[i].forward->ele,ele) < 0)))
            x = x->level[i].forward;
        update[i] = x;
    }

    /* update the robj pointer inside the skip list record. */
    x = x->level[0].forward;
    serverAssert(x && score == x->score && x->ele==oldele);
    if (newele)
        x->ele = newele;

    /* try to defrag the skiplist record itself */
    newx = activeDefragAlloc(x);
    if (newx) {
        zslUpdateNode(zsl, x, newx, update);
        return &newx->score;
    }
    return NULL;
}

/* Defrag helper for sorted set.
 * Defrag a single dict entry key name, and corresponding skiplist struct */
long activeDefragZsetEntry(zset *zs, dictEntry *de) {
    sds newsds;
    double* newscore;
    long defragged = 0;
    sds sdsele = dictGetKey(de);
    if ((newsds = activeDefragSds(sdsele)))
        defragged++, de->key = newsds;
    newscore = zslDefrag(zs->zsl, *(double*)dictGetVal(de), sdsele, newsds);
    if (newscore) {
        dictSetVal(zs->dict, de, newscore);
        defragged++;
    }
    return defragged;
}

#define DEFRAG_SDS_DICT_NO_VAL 0
#define DEFRAG_SDS_DICT_VAL_IS_SDS 1
#define DEFRAG_SDS_DICT_VAL_IS_STROB 2
#define DEFRAG_SDS_DICT_VAL_VOID_PTR 3

/* Defrag a dict with sds key and optional value (either ptr, sds or robj string) */
long activeDefragSdsDict(dict* d, int val_type) {
    dictIterator *di;
    dictEntry *de;
    long defragged = 0;
    di = dictGetIterator(d);
    while((de = dictNext(di)) != NULL) {
        sds sdsele = dictGetKey(de), newsds;
        if ((newsds = activeDefragSds(sdsele)))
            de->key = newsds, defragged++;
        /* defrag the value */
        if (val_type == DEFRAG_SDS_DICT_VAL_IS_SDS) {
            sdsele = dictGetVal(de);
            if ((newsds = activeDefragSds(sdsele)))
                de->v.val = newsds, defragged++;
        } else if (val_type == DEFRAG_SDS_DICT_VAL_IS_STROB) {
            robj *newele, *ele = dictGetVal(de);
            if ((newele = activeDefragStringOb(ele, &defragged)))
                de->v.val = newele;
        } else if (val_type == DEFRAG_SDS_DICT_VAL_VOID_PTR) {
            void *newptr, *ptr = dictGetVal(de);
            if ((newptr = activeDefragAlloc(ptr)))
                de->v.val = newptr, defragged++;
        }
        defragged += dictIterDefragEntry(di);
    }
    dictReleaseIterator(di);
    return defragged;
}

/* Defrag a list of ptr, sds or robj string values */
long activeDefragList(list *l, int val_type) {
    long defragged = 0;
    listNode *ln, *newln;
    for (ln = l->head; ln; ln = ln->next) {
        if ((newln = activeDefragAlloc(ln))) {
            if (newln->prev)
                newln->prev->next = newln;
            else
                l->head = newln;
            if (newln->next)
                newln->next->prev = newln;
            else
                l->tail = newln;
            ln = newln;
            defragged++;
        }
        if (val_type == DEFRAG_SDS_DICT_VAL_IS_SDS) {
            sds newsds, sdsele = ln->value;
            if ((newsds = activeDefragSds(sdsele)))
                ln->value = newsds, defragged++;
        } else if (val_type == DEFRAG_SDS_DICT_VAL_IS_STROB) {
            robj *newele, *ele = ln->value;
            if ((newele = activeDefragStringOb(ele, &defragged)))
                ln->value = newele;
        } else if (val_type == DEFRAG_SDS_DICT_VAL_VOID_PTR) {
            void *newptr, *ptr = ln->value;
            if ((newptr = activeDefragAlloc(ptr)))
                ln->value = newptr, defragged++;
        }
    }
    return defragged;
}