text: /* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
  /*
   * Slabs memory allocation, based on powers-of-N. Slabs are up to 1MB in size
   * and are divided into chunks. The chunk sizes start off at the size of the
   * "item" structure plus space for a small key and value. They increase by
   * a multiplier factor from there, up to half the maximum slab size. The last
   * slab size is always 1MB, since that's the maximum item size allowed by the
   * memcached protocol.
   */
  #include "memcached.h"
  #include <sys/stat.h>
  #include <sys/socket.h>
  #include <sys/signal.h>
  #include <sys/resource.h>
  #include <fcntl.h>
  #include <netinet/in.h>
  #include <errno.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  #include <assert.h>
  #include <pthread.h>
  
  /* powers-of-N allocation structures */
  
  typedef struct {
      unsigned int size;      /* sizes of items */
      unsigned int perslab;   /* how many items per slab */
  
      void **slots;           /* list of item ptrs */
      unsigned int sl_total;  /* size of previous array */
      unsigned int sl_curr;   /* first free slot */
  
      void *end_page_ptr;         /* pointer to next free item at end of page, or 0 */
      unsigned int end_page_free; /* number of items remaining at end of last alloced page */
  
      unsigned int slabs;     /* how many slabs were allocated for this class */
  
      void **slab_list;       /* array of slab pointers */
      unsigned int list_size; /* size of prev array */
  
      unsigned int killing;  /* index+1 of dying slab, or zero if none */
      size_t requested; /* The number of requested bytes */
  } slabclass_t;
  
  static slabclass_t slabclass[MAX_NUMBER_OF_SLAB_CLASSES];
  static size_t mem_limit = 0;
  static size_t mem_malloced = 0;
  static int power_largest;
  
  static void *mem_base = NULL;
  static void *mem_current = NULL;
  static size_t mem_avail = 0;
  
  /**
   * Access to the slab allocator is protected by this lock
   */
  static pthread_mutex_t slabs_lock = PTHREAD_MUTEX_INITIALIZER;
  
  /*
   * Forward Declarations
   */
  static int do_slabs_newslab(const unsigned int id);
  static void *memory_allocate(size_t size);
  
  #ifndef DONT_PREALLOC_SLABS
  /* Preallocate as many slab pages as possible (called from slabs_init)
     on start-up, so users don't get confused out-of-memory errors when
     they do have free (in-slab) space, but no space to make new slabs.
     if maxslabs is 18 (POWER_LARGEST - POWER_SMALLEST + 1), then all
     slab types can be made.  if max memory is less than 18 MB, only the
     smaller ones will be made.  */
  static void slabs_preallocate (const unsigned int maxslabs);
  #endif
  
  /*
   * Figures out which slab class (chunk size) is required to store an item of
   * a given size.
   *
   * Given object size, return id to use when allocating/freeing memory for object
   * 0 means error: can't store such a large object
   */
  
  unsigned int slabs_clsid(const size_t size) {
      int res = POWER_SMALLEST;
  
      if (size == 0)
          return 0;
      while (size > slabclass[res].size)
          if (res++ == power_largest)     /* won't fit in the biggest slab */
              return 0;
      return res;
  }
  
  /**
   * Determines the chunk sizes and initializes the slab class descriptors
   * accordingly.
   */
  void slabs_init(const size_t limit, const double factor, const bool prealloc) {
      int i = POWER_SMALLEST - 1;
      unsigned int size = sizeof(item) + settings.chunk_size;
  
      mem_limit = limit;
  
      if (prealloc) {
          /* Allocate everything in a big chunk with malloc */
          mem_base = malloc(mem_limit);
          if (mem_base != NULL) {
              mem_current = mem_base;
              mem_avail = mem_limit;
          } else {
              fprintf(stderr, "Warning: Failed to allocate requested memory in"
                      " one large chunk.\nWill allocate in smaller chunks\n");
          }
      }
  
      memset(slabclass, 0, sizeof(slabclass));
  
      while (++i < POWER_LARGEST && size <= settings.item_size_max / factor) {
          /* Make sure items are always n-byte aligned */
          if (size % CHUNK_ALIGN_BYTES)
              size += CHUNK_ALIGN_BYTES - (size % CHUNK_ALIGN_BYTES);
  
          slabclass[i].size = size;
          slabclass[i].perslab = settings.item_size_max / slabclass[i].size;
          size *= factor;
          if (settings.verbose > 1) {
              fprintf(stderr, "slab class %3d: chunk size %9u perslab %7u\n",
                      i, slabclass[i].size, slabclass[i].perslab);
          }
      }
  
      power_largest = i;
      slabclass[power_largest].size = settings.item_size_max;
      slabclass[power_largest].perslab = 1;
      if (settings.verbose > 1) {
          fprintf(stderr, "slab class %3d: chunk size %9u perslab %7u\n",
                  i, slabclass[i].size, slabclass[i].perslab);
      }
  
      /* for the test suite:  faking of how much we've already malloc'd */
      {
          char *t_initial_malloc = getenv("T_MEMD_INITIAL_MALLOC");
          if (t_initial_malloc) {
              mem_malloced = (size_t)atol(t_initial_malloc);
          }
  
      }
  
  #ifndef DONT_PREALLOC_SLABS
      {
          char *pre_alloc = getenv("T_MEMD_SLABS_ALLOC");
  
          if (pre_alloc == NULL || atoi(pre_alloc) != 0) {
              slabs_preallocate(power_largest);
          }
      }
  #endif
  }
  
  #ifndef DONT_PREALLOC_SLABS
  static void slabs_preallocate (const unsigned int maxslabs) {
      int i;
      unsigned int prealloc = 0;
  
      /* pre-allocate a 1MB slab in every size class so people don't get
         confused by non-intuitive "SERVER_ERROR out of memory"
         messages.  this is the most common question on the mailing
         list.  if you really don't want this, you can rebuild without
         these three lines.  */
  
      for (i = POWER_SMALLEST; i <= POWER_LARGEST; i++) {
          if (++prealloc > maxslabs)
              return;
          do_slabs_newslab(i);
      }
  
  }
  #endif
  
  static int grow_slab_list (const unsigned int id) {
      slabclass_t *p = &slabclass[id];
      if (p->slabs == p->list_size) {
          size_t new_size =  (p->list_size != 0) ? p->list_size * 2 : 16;
          void *new_list = realloc(p->slab_list, new_size * sizeof(void *));
          if (new_list == 0) return 0;
          p->list_size = new_size;
          p->slab_list = new_list;
      }
      return 1;
  }
  
  static int do_slabs_newslab(const unsigned int id) {
      slabclass_t *p = &slabclass[id];
      int len = p->size * p->perslab;
      char *ptr;
  
      if ((mem_limit && mem_malloced + len > mem_limit && p->slabs > 0) ||
          (grow_slab_list(id) == 0) ||
          ((ptr = memory_allocate((size_t)len)) == 0)) {
  
          MEMCACHED_SLABS_SLABCLASS_ALLOCATE_FAILED(id);
          return 0;
      }
  
      memset(ptr, 0, (size_t)len);
      p->end_page_ptr = ptr;
      p->end_page_free = p->perslab;
  
      p->slab_list[p->slabs++] = ptr;
      mem_malloced += len;
      MEMCACHED_SLABS_SLABCLASS_ALLOCATE(id);
  
      return 1;
  }
  
  /*@null@*/
  static void *do_slabs_alloc(const size_t size, unsigned int id) {
      slabclass_t *p;
      void *ret = NULL;
  
      if (id < POWER_SMALLEST || id > power_largest) {
          MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
          return NULL;
      }
  
      p = &slabclass[id];
      assert(p->sl_curr == 0 || ((item *)p->slots[p->sl_curr - 1])->slabs_clsid == 0);
  
  #ifdef USE_SYSTEM_MALLOC
      if (mem_limit && mem_malloced + size > mem_limit) {
          MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
          return 0;
      }
      mem_malloced += size;
      ret = malloc(size);
      MEMCACHED_SLABS_ALLOCATE(size, id, 0, ret);
      return ret;
  #endif
  
      /* fail unless we have space at the end of a recently allocated page,
         we have something on our freelist, or we could allocate a new page */
      if (! (p->end_page_ptr != 0 || p->sl_curr != 0 ||
             do_slabs_newslab(id) != 0)) {
          /* We don't have more memory available */
          ret = NULL;
      } else if (p->sl_curr != 0) {
          /* return off our freelist */
          ret = p->slots[--p->sl_curr];
      } else {
          /* if we recently allocated a whole page, return from that */
          assert(p->end_page_ptr != NULL);
          ret = p->end_page_ptr;
          if (--p->end_page_free != 0) {
              p->end_page_ptr = ((caddr_t)p->end_page_ptr) + p->size;
          } else {
              p->end_page_ptr = 0;
          }
      }
  
      if (ret) {
          p->requested += size;
          MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
      } else {
          MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
      }
  
      return ret;
  }
  
  static void do_slabs_free(void *ptr, const size_t size, unsigned int id) {
      slabclass_t *p;
  
      assert(((item *)ptr)->slabs_clsid == 0);
      assert(id >= POWER_SMALLEST && id <= power_largest);
      if (id < POWER_SMALLEST || id > power_largest)
          return;
  
      MEMCACHED_SLABS_FREE(size, id, ptr);
      p = &slabclass[id];
  
  #ifdef USE_SYSTEM_MALLOC
      mem_malloced -= size;
      free(ptr);
      return;
  #endif
  
      if (p->sl_curr == p->sl_total) { /* need more space on the free list */
          int new_size = (p->sl_total != 0) ? p->sl_total * 2 : 16;  /* 16 is arbitrary */
          void **new_slots = realloc(p->slots, new_size * sizeof(void *));
          if (new_slots == 0)
              return;
          p->slots = new_slots;
          p->sl_total = new_size;
      }
      p->slots[p->sl_curr++] = ptr;
      p->requested -= size;
      return;
  }
  
  static int nz_strcmp(int nzlength, const char *nz, const char *z) {
      int zlength=strlen(z);
      return (zlength == nzlength) && (strncmp(nz, z, zlength) == 0) ? 0 : -1;
  }
  
  bool get_stats(const char *stat_type, int nkey, ADD_STAT add_stats, void *c) {
      bool ret = true;
  
      if (add_stats != NULL) {
          if (!stat_type) {
              /* prepare general statistics for the engine */
              APPEND_STAT("bytes", "%llu", (unsigned long long)stats.curr_bytes);
              APPEND_STAT("curr_items", "%u", stats.curr_items);
              APPEND_STAT("total_items", "%u", stats.total_items);
              APPEND_STAT("evictions", "%llu",
                          (unsigned long long)stats.evictions);
          } else if (nz_strcmp(nkey, stat_type, "items") == 0) {
              item_stats(add_stats, c);
          } else if (nz_strcmp(nkey, stat_type, "slabs") == 0) {
              slabs_stats(add_stats, c);
          } else if (nz_strcmp(nkey, stat_type, "sizes") == 0) {
              item_stats_sizes(add_stats, c);
          } else {
              ret = false;
          }
      } else {
          ret = false;
      }
  
      return ret;
  }
  
  /*@null@*/
  static void do_slabs_stats(ADD_STAT add_stats, void *c) {
      int i, total;
      /* Get the per-thread stats which contain some interesting aggregates */
      struct thread_stats thread_stats;
      threadlocal_stats_aggregate(&thread_stats);
  
      total = 0;
      for(i = POWER_SMALLEST; i <= power_largest; i++) {
          slabclass_t *p = &slabclass[i];
          if (p->slabs != 0) {
              uint32_t perslab, slabs;
              slabs = p->slabs;
              perslab = p->perslab;
  
              char key_str[STAT_KEY_LEN];
              char val_str[STAT_VAL_LEN];
              int klen = 0, vlen = 0;
  
              APPEND_NUM_STAT(i, "chunk_size", "%u", p->size);
              APPEND_NUM_STAT(i, "chunks_per_page", "%u", perslab);
              APPEND_NUM_STAT(i, "total_pages", "%u", slabs);
              APPEND_NUM_STAT(i, "total_chunks", "%u", slabs * perslab);
              APPEND_NUM_STAT(i, "used_chunks", "%u",
                              slabs*perslab - p->sl_curr - p->end_page_free);
              APPEND_NUM_STAT(i, "free_chunks", "%u", p->sl_curr);
              APPEND_NUM_STAT(i, "free_chunks_end", "%u", p->end_page_free);
              APPEND_NUM_STAT(i, "mem_requested", "%llu",
                              (unsigned long long)p->requested);
              APPEND_NUM_STAT(i, "get_hits", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].get_hits);
              APPEND_NUM_STAT(i, "cmd_set", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].set_cmds);
              APPEND_NUM_STAT(i, "delete_hits", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].delete_hits);
              APPEND_NUM_STAT(i, "incr_hits", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].incr_hits);
              APPEND_NUM_STAT(i, "decr_hits", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].decr_hits);
              APPEND_NUM_STAT(i, "cas_hits", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].cas_hits);
              APPEND_NUM_STAT(i, "cas_badval", "%llu",
                      (unsigned long long)thread_stats.slab_stats[i].cas_badval);
  
              total++;
          }
      }
  
      /* add overall slab stats and append terminator */
  
      APPEND_STAT("active_slabs", "%d", total);
      APPEND_STAT("total_malloced", "%llu", (unsigned long long)mem_malloced);
      add_stats(NULL, 0, NULL, 0, c);
  }
  
  static void *memory_allocate(size_t size) {
      void *ret;
  
      if (mem_base == NULL) {
          /* We are not using a preallocated large memory chunk */
          ret = malloc(size);
      } else {
          ret = mem_current;
  
          if (size > mem_avail) {
              return NULL;
          }
  
          /* mem_current pointer _must_ be aligned!!! */
          if (size % CHUNK_ALIGN_BYTES) {
              size += CHUNK_ALIGN_BYTES - (size % CHUNK_ALIGN_BYTES);
          }
  
          mem_current = ((char*)mem_current) + size;
          if (size < mem_avail) {
              mem_avail -= size;
          } else {
              mem_avail = 0;
          }
      }
  
      return ret;
  }
  
  void *slabs_alloc(size_t size, unsigned int id) {
      void *ret;
  
      pthread_mutex_lock(&slabs_lock);
      ret = do_slabs_alloc(size, id);
      pthread_mutex_unlock(&slabs_lock);
      return ret;
  }
  
  void slabs_free(void *ptr, size_t size, unsigned int id) {
      pthread_mutex_lock(&slabs_lock);
      do_slabs_free(ptr, size, id);
      pthread_mutex_unlock(&slabs_lock);
  }
  
  void slabs_stats(ADD_STAT add_stats, void *c) {
      pthread_mutex_lock(&slabs_lock);
      do_slabs_stats(add_stats, c);
      pthread_mutex_unlock(&slabs_lock);
  }
  