/Users/deen/code/yugabyte-db/src/postgres/src/backend/utils/mmgr/slab.c

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/*-------------------------------------------------------------------------
 *
 * slab.c
 *    SLAB allocator definitions.
 *
 * SLAB is a MemoryContext implementation designed for cases where large
 * numbers of equally-sized objects are allocated (and freed).
 *
 *
 * Portions Copyright (c) 2017-2018, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/mmgr/slab.c
 *
 *
 * NOTE:
 *  The constant allocation size allows significant simplification and various
 *  optimizations over more general purpose allocators. The blocks are carved
 *  into chunks of exactly the right size (plus alignment), not wasting any
 *  memory.
 *
 *  The information about free chunks is maintained both at the block level and
 *  global (context) level. This is possible as the chunk size (and thus also
 *  the number of chunks per block) is fixed.
 *
 *  On each block, free chunks are tracked in a simple linked list. Contents
 *  of free chunks is replaced with an index of the next free chunk, forming
 *  a very simple linked list. Each block also contains a counter of free
 *  chunks. Combined with the local block-level freelist, it makes it trivial
 *  to eventually free the whole block.
 *
 *  At the context level, we use 'freelist' to track blocks ordered by number
 *  of free chunks, starting with blocks having a single allocated chunk, and
 *  with completely full blocks on the tail.
 *
 *  This also allows various optimizations - for example when searching for
 *  free chunk, the allocator reuses space from the fullest blocks first, in
 *  the hope that some of the less full blocks will get completely empty (and
 *  returned back to the OS).
 *
 *  For each block, we maintain pointer to the first free chunk - this is quite
 *  cheap and allows us to skip all the preceding used chunks, eliminating
 *  a significant number of lookups in many common usage patters. In the worst
 *  case this performs as if the pointer was not maintained.
 *
 *  We cache the freelist index for the blocks with the fewest free chunks
 *  (minFreeChunks), so that we don't have to search the freelist on every
 *  SlabAlloc() call, which is quite expensive.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "utils/memdebug.h"
#include "utils/memutils.h"
#include "lib/ilist.h"


/*
 * SlabContext is a specialized implementation of MemoryContext.
 */
typedef struct SlabContext
{
  MemoryContextData header; /* Standard memory-context fields */
  /* Allocation parameters for this context: */
  Size    chunkSize;    /* chunk size */
  Size    fullChunkSize;  /* chunk size including header and alignment */
  Size    blockSize;    /* block size */
  Size    headerSize;   /* allocated size of context header */
  int     chunksPerBlock; /* number of chunks per block */
  int     minFreeChunks;  /* min number of free chunks in any block */
  int     nblocks;    /* number of blocks allocated */
  /* blocks with free space, grouped by number of free chunks: */
  dlist_head  freelist[FLEXIBLE_ARRAY_MEMBER];
} SlabContext;

/*
 * SlabBlock
 *    Structure of a single block in SLAB allocator.
 *
 * node: doubly-linked list of blocks in global freelist
 * nfree: number of free chunks in this block
 * firstFreeChunk: index of the first free chunk
 */
typedef struct SlabBlock
{
  dlist_node  node;     /* doubly-linked list */
  int     nfree;      /* number of free chunks */
  int     firstFreeChunk; /* index of the first free chunk in the block */
} SlabBlock;

/*
 * SlabChunk
 *    The prefix of each piece of memory in a SlabBlock
 *
 * Note: to meet the memory context APIs, the payload area of the chunk must
 * be maxaligned, and the "slab" link must be immediately adjacent to the
 * payload area (cf. GetMemoryChunkContext).  Since we support no machines on
 * which MAXALIGN is more than twice sizeof(void *), this happens without any
 * special hacking in this struct declaration.  But there is a static
 * assertion below that the alignment is done correctly.
 */
typedef struct SlabChunk
{
  SlabBlock  *block;      /* block owning this chunk */
  SlabContext *slab;      /* owning context */
  /* there must not be any padding to reach a MAXALIGN boundary here! */
} SlabChunk;


#define SlabPointerGetChunk(ptr)  \
  ((SlabChunk *)(((char *)(ptr)) - sizeof(SlabChunk)))
#define SlabChunkGetPointer(chk)  \
  ((void *)(((char *)(chk)) + sizeof(SlabChunk)))
#define SlabBlockGetChunk(slab, block, idx) \
  ((SlabChunk *) ((char *) (block) + sizeof(SlabBlock)  \
          + (idx * slab->fullChunkSize)))
#define SlabBlockStart(block) \
  ((char *) block + sizeof(SlabBlock))
#define SlabChunkIndex(slab, block, chunk)  \
  (((char *) chunk - SlabBlockStart(block)) / slab->fullChunkSize)

/*
 * These functions implement the MemoryContext API for Slab contexts.
 */
static void *SlabAlloc(MemoryContext context, Size size);
static void SlabFree(MemoryContext context, void *pointer);
static void *SlabRealloc(MemoryContext context, void *pointer, Size size);
static void SlabReset(MemoryContext context);
static void SlabDelete(MemoryContext context);
static Size SlabGetChunkSpace(MemoryContext context, void *pointer);
static bool SlabIsEmpty(MemoryContext context);
static void SlabStats(MemoryContext context,
      MemoryStatsPrintFunc printfunc, void *passthru,
      MemoryContextCounters *totals);
#ifdef MEMORY_CONTEXT_CHECKING
static void SlabCheck(MemoryContext context);
#endif

/*
 * This is the virtual function table for Slab contexts.
 */
static const MemoryContextMethods SlabMethods = {
  SlabAlloc,
  SlabFree,
  SlabRealloc,
  SlabReset,
  SlabDelete,
  SlabGetChunkSpace,
  SlabIsEmpty,
  SlabStats
#ifdef MEMORY_CONTEXT_CHECKING
  ,SlabCheck
#endif
};

/* ----------
 * Debug macros
 * ----------
 */
#ifdef HAVE_ALLOCINFO
#define SlabFreeInfo(_cxt, _chunk) \
      fprintf(stderr, "SlabFree: %s: %p, %zu\n", \
        (_cxt)->header.name, (_chunk), (_chunk)->header.size)
#define SlabAllocInfo(_cxt, _chunk) \
      fprintf(stderr, "SlabAlloc: %s: %p, %zu\n", \
        (_cxt)->header.name, (_chunk), (_chunk)->header.size)
#else
#define SlabFreeInfo(_cxt, _chunk)
#define SlabAllocInfo(_cxt, _chunk)
#endif


/*
 * SlabContextCreate
 *    Create a new Slab context.
 *
 * parent: parent context, or NULL if top-level context
 * name: name of context (must be statically allocated)
 * blockSize: allocation block size
 * chunkSize: allocation chunk size
 *
 * The chunkSize may not exceed:
 *    MAXALIGN_DOWN(SIZE_MAX) - MAXALIGN(sizeof(SlabBlock)) - SLAB_CHUNKHDRSZ
 */
MemoryContext
SlabContextCreate(MemoryContext parent,
          const char *name,
          Size blockSize,
          Size chunkSize)
{
  int     chunksPerBlock;
  Size    fullChunkSize;
  Size    freelistSize;
  Size    headerSize;
  SlabContext *slab;
  int     i;

  /* Assert we padded SlabChunk properly */
  StaticAssertStmt(sizeof(SlabChunk) == MAXALIGN(sizeof(SlabChunk)),
           "sizeof(SlabChunk) is not maxaligned");
  StaticAssertStmt(offsetof(SlabChunk, slab) + sizeof(MemoryContext) ==
           sizeof(SlabChunk),
           "padding calculation in SlabChunk is wrong");

  /* Make sure the linked list node fits inside a freed chunk */
  if (chunkSize < sizeof(int))
    chunkSize = sizeof(int);

  /* chunk, including SLAB header (both addresses nicely aligned) */
  fullChunkSize = sizeof(SlabChunk) + MAXALIGN(chunkSize);

  /* Make sure the block can store at least one chunk. */
  if (blockSize < fullChunkSize + sizeof(SlabBlock))
    elog(ERROR, "block size %zu for slab is too small for %zu chunks",
       blockSize, chunkSize);

  /* Compute maximum number of chunks per block */
  chunksPerBlock = (blockSize - sizeof(SlabBlock)) / fullChunkSize;

  /* The freelist starts with 0, ends with chunksPerBlock. */
  freelistSize = sizeof(dlist_head) * (chunksPerBlock + 1);

  /*
   * Allocate the context header.  Unlike aset.c, we never try to combine
   * this with the first regular block; not worth the extra complication.
   */

  /* Size of the memory context header */
  headerSize = offsetof(SlabContext, freelist) + freelistSize;

  slab = (SlabContext *) malloc(headerSize);
  if (slab == NULL)
  {
    MemoryContextStats(TopMemoryContext);
    ereport(ERROR,
        (errcode(ERRCODE_OUT_OF_MEMORY),
         errmsg("out of memory"),
         errdetail("Failed while creating memory context \"%s\".",
               name)));
  }

  /*
   * Avoid writing code that can fail between here and MemoryContextCreate;
   * we'd leak the header if we ereport in this stretch.
   */

  /* Fill in SlabContext-specific header fields */
  slab->chunkSize = chunkSize;
  slab->fullChunkSize = fullChunkSize;
  slab->blockSize = blockSize;
  slab->headerSize = headerSize;
  slab->chunksPerBlock = chunksPerBlock;
  slab->minFreeChunks = 0;
  slab->nblocks = 0;

  /* initialize the freelist slots */
  for (i = 0; i < (slab->chunksPerBlock + 1); i++)
    dlist_init(&slab->freelist[i]);

  /* Finally, do the type-independent part of context creation */
  MemoryContextCreate((MemoryContext) slab,
            T_SlabContext,
            &SlabMethods,
            parent,
            name);

  return (MemoryContext) slab;
}

/*
 * SlabReset
 *    Frees all memory which is allocated in the given set.
 *
 * The code simply frees all the blocks in the context - we don't keep any
 * keeper blocks or anything like that.
 */
static void
SlabReset(MemoryContext context)
{
  int     i;
  SlabContext *slab = castNode(SlabContext, context);

  Assert(slab);

#ifdef MEMORY_CONTEXT_CHECKING
  /* Check for corruption and leaks before freeing */
  SlabCheck(context);
#endif

  /* walk over freelists and free the blocks */
  for (i = 0; i <= slab->chunksPerBlock; i++)
  {
    dlist_mutable_iter miter;

    dlist_foreach_modify(miter, &slab->freelist[i])
    {
      SlabBlock  *block = dlist_container(SlabBlock, node, miter.cur);

      dlist_delete(miter.cur);

#ifdef CLOBBER_FREED_MEMORY
      wipe_mem(block, slab->blockSize);
#endif
      free(block);
      slab->nblocks--;
    }
  }

  slab->minFreeChunks = 0;

  Assert(slab->nblocks == 0);
}

/*
 * SlabDelete
 *    Free all memory which is allocated in the given context.
 */
static void
SlabDelete(MemoryContext context)
{
  /* Reset to release all the SlabBlocks */
  SlabReset(context);
  /* And free the context header */
  free(context);
}

/*
 * SlabAlloc
 *    Returns pointer to allocated memory of given size or NULL if
 *    request could not be completed; memory is added to the slab.
 */
static void *
SlabAlloc(MemoryContext context, Size size)
{
  SlabContext *slab = castNode(SlabContext, context);
  SlabBlock  *block;
  SlabChunk  *chunk;
  int     idx;

  Assert(slab);

  Assert((slab->minFreeChunks >= 0) &&
       (slab->minFreeChunks < slab->chunksPerBlock));

  /* make sure we only allow correct request size */
  if (size != slab->chunkSize)
    elog(ERROR, "unexpected alloc chunk size %zu (expected %zu)",
       size, slab->chunkSize);

  /*
   * If there are no free chunks in any existing block, create a new block
   * and put it to the last freelist bucket.
   *
   * slab->minFreeChunks == 0 means there are no blocks with free chunks,
   * thanks to how minFreeChunks is updated at the end of SlabAlloc().
   */
  if (slab->minFreeChunks == 0)
  {
    block = (SlabBlock *) malloc(slab->blockSize);

    if (block == NULL)
      return NULL;

    block->nfree = slab->chunksPerBlock;
    block->firstFreeChunk = 0;

    /*
     * Put all the chunks on a freelist. Walk the chunks and point each
     * one to the next one.
     */
    for (idx = 0; idx < slab->chunksPerBlock; idx++)
    {
      chunk = SlabBlockGetChunk(slab, block, idx);
      *(int32 *) SlabChunkGetPointer(chunk) = (idx + 1);
    }

    /*
     * And add it to the last freelist with all chunks empty.
     *
     * We know there are no blocks in the freelist, otherwise we wouldn't
     * need a new block.
     */
    Assert(dlist_is_empty(&slab->freelist[slab->chunksPerBlock]));

    dlist_push_head(&slab->freelist[slab->chunksPerBlock], &block->node);

    slab->minFreeChunks = slab->chunksPerBlock;
    slab->nblocks += 1;
  }

  /* grab the block from the freelist (even the new block is there) */
  block = dlist_head_element(SlabBlock, node,
                 &slab->freelist[slab->minFreeChunks]);

  /* make sure we actually got a valid block, with matching nfree */
  Assert(block != NULL);
  Assert(slab->minFreeChunks == block->nfree);
  Assert(block->nfree > 0);

  /* we know index of the first free chunk in the block */
  idx = block->firstFreeChunk;

  /* make sure the chunk index is valid, and that it's marked as empty */
  Assert((idx >= 0) && (idx < slab->chunksPerBlock));

  /* compute the chunk location block start (after the block header) */
  chunk = SlabBlockGetChunk(slab, block, idx);

  /*
   * Update the block nfree count, and also the minFreeChunks as we've
   * decreased nfree for a block with the minimum number of free chunks
   * (because that's how we chose the block).
   */
  block->nfree--;
  slab->minFreeChunks = block->nfree;

  /*
   * Remove the chunk from the freelist head. The index of the next free
   * chunk is stored in the chunk itself.
   */
  VALGRIND_MAKE_MEM_DEFINED(SlabChunkGetPointer(chunk), sizeof(int32));
  block->firstFreeChunk = *(int32 *) SlabChunkGetPointer(chunk);

  Assert(block->firstFreeChunk >= 0);
  Assert(block->firstFreeChunk <= slab->chunksPerBlock);

  Assert((block->nfree != 0 &&
      block->firstFreeChunk < slab->chunksPerBlock) ||
       (block->nfree == 0 &&
      block->firstFreeChunk == slab->chunksPerBlock));

  /* move the whole block to the right place in the freelist */
  dlist_delete(&block->node);
  dlist_push_head(&slab->freelist[block->nfree], &block->node);

  /*
   * And finally update minFreeChunks, i.e. the index to the block with the
   * lowest number of free chunks. We only need to do that when the block
   * got full (otherwise we know the current block is the right one). We'll
   * simply walk the freelist until we find a non-empty entry.
   */
  if (slab->minFreeChunks == 0)
  {
    for (idx = 1; idx <= slab->chunksPerBlock; idx++)
    {
      if (dlist_is_empty(&slab->freelist[idx]))
        continue;

      /* found a non-empty freelist */
      slab->minFreeChunks = idx;
      break;
    }
  }

  if (slab->minFreeChunks == slab->chunksPerBlock)
    slab->minFreeChunks = 0;

  /* Prepare to initialize the chunk header. */
  VALGRIND_MAKE_MEM_UNDEFINED(chunk, sizeof(SlabChunk));

  chunk->block = block;
  chunk->slab = slab;

#ifdef MEMORY_CONTEXT_CHECKING
  /* slab mark to catch clobber of "unused" space */
  if (slab->chunkSize < (slab->fullChunkSize - sizeof(SlabChunk)))
  {
    set_sentinel(SlabChunkGetPointer(chunk), size);
    VALGRIND_MAKE_MEM_NOACCESS(((char *) chunk) +
                   sizeof(SlabChunk) + slab->chunkSize,
                   slab->fullChunkSize -
                   (slab->chunkSize + sizeof(SlabChunk)));
  }
#endif
#ifdef RANDOMIZE_ALLOCATED_MEMORY
  /* fill the allocated space with junk */
  randomize_mem((char *) SlabChunkGetPointer(chunk), size);
#endif

  SlabAllocInfo(slab, chunk);
  return SlabChunkGetPointer(chunk);
}

/*
 * SlabFree
 *    Frees allocated memory; memory is removed from the slab.
 */
static void
SlabFree(MemoryContext context, void *pointer)
{
  int     idx;
  SlabContext *slab = castNode(SlabContext, context);
  SlabChunk  *chunk = SlabPointerGetChunk(pointer);
  SlabBlock  *block = chunk->block;

  SlabFreeInfo(slab, chunk);

#ifdef MEMORY_CONTEXT_CHECKING
  /* Test for someone scribbling on unused space in chunk */
  if (slab->chunkSize < (slab->fullChunkSize - sizeof(SlabChunk)))
    if (!sentinel_ok(pointer, slab->chunkSize))
      elog(WARNING, "detected write past chunk end in %s %p",
         slab->header.name, chunk);
#endif

  /* compute index of the chunk with respect to block start */
  idx = SlabChunkIndex(slab, block, chunk);

  /* add chunk to freelist, and update block nfree count */
  *(int32 *) pointer = block->firstFreeChunk;
  block->firstFreeChunk = idx;
  block->nfree++;

  Assert(block->nfree > 0);
  Assert(block->nfree <= slab->chunksPerBlock);

#ifdef CLOBBER_FREED_MEMORY
  /* XXX don't wipe the int32 index, used for block-level freelist */
  wipe_mem((char *) pointer + sizeof(int32),
       slab->chunkSize - sizeof(int32));
#endif

  /* remove the block from a freelist */
  dlist_delete(&block->node);

  /*
   * See if we need to update the minFreeChunks field for the slab - we only
   * need to do that if there the block had that number of free chunks
   * before we freed one. In that case, we check if there still are blocks
   * in the original freelist and we either keep the current value (if there
   * still are blocks) or increment it by one (the new block is still the
   * one with minimum free chunks).
   *
   * The one exception is when the block will get completely free - in that
   * case we will free it, se we can't use it for minFreeChunks. It however
   * means there are no more blocks with free chunks.
   */
  if (slab->minFreeChunks == (block->nfree - 1))
  {
    /* Have we removed the last chunk from the freelist? */
    if (dlist_is_empty(&slab->freelist[slab->minFreeChunks]))
    {
      /* but if we made the block entirely free, we'll free it */
      if (block->nfree == slab->chunksPerBlock)
        slab->minFreeChunks = 0;
      else
        slab->minFreeChunks++;
    }
  }

  /* If the block is now completely empty, free it. */
  if (block->nfree == slab->chunksPerBlock)
  {
    free(block);
    slab->nblocks--;
  }
  else
    dlist_push_head(&slab->freelist[block->nfree], &block->node);

  Assert(slab->nblocks >= 0);
}

/*
 * SlabRealloc
 *    Change the allocated size of a chunk.
 *
 * As Slab is designed for allocating equally-sized chunks of memory, it can't
 * do an actual chunk size change.  We try to be gentle and allow calls with
 * exactly the same size, as in that case we can simply return the same
 * chunk.  When the size differs, we throw an error.
 *
 * We could also allow requests with size < chunkSize.  That however seems
 * rather pointless - Slab is meant for chunks of constant size, and moreover
 * realloc is usually used to enlarge the chunk.
 */
static void *
SlabRealloc(MemoryContext context, void *pointer, Size size)
{
  SlabContext *slab = castNode(SlabContext, context);

  Assert(slab);

  /* can't do actual realloc with slab, but let's try to be gentle */
  if (size == slab->chunkSize)
    return pointer;

  elog(ERROR, "slab allocator does not support realloc()");
  return NULL;       /* keep compiler quiet */
}

/*
 * SlabGetChunkSpace
 *    Given a currently-allocated chunk, determine the total space
 *    it occupies (including all memory-allocation overhead).
 */
static Size
SlabGetChunkSpace(MemoryContext context, void *pointer)
{
  SlabContext *slab = castNode(SlabContext, context);

  Assert(slab);

  return slab->fullChunkSize;
}

/*
 * SlabIsEmpty
 *    Is an Slab empty of any allocated space?
 */
static bool
SlabIsEmpty(MemoryContext context)
{
  SlabContext *slab = castNode(SlabContext, context);

  Assert(slab);

  return (slab->nblocks == 0);
}

/*
 * SlabStats
 *    Compute stats about memory consumption of a Slab context.
 *
 * printfunc: if not NULL, pass a human-readable stats string to this.
 * passthru: pass this pointer through to printfunc.
 * totals: if not NULL, add stats about this context into *totals.
 */
static void
SlabStats(MemoryContext context,
      MemoryStatsPrintFunc printfunc, void *passthru,
      MemoryContextCounters *totals)
{
  SlabContext *slab = castNode(SlabContext, context);
  Size    nblocks = 0;
  Size    freechunks = 0;
  Size    totalspace;
  Size    freespace = 0;
  int     i;

  /* Include context header in totalspace */
  totalspace = slab->headerSize;

  for (i = 0; i <= slab->chunksPerBlock; i++)
  {
    dlist_iter  iter;

    dlist_foreach(iter, &slab->freelist[i])
    {
      SlabBlock  *block = dlist_container(SlabBlock, node, iter.cur);

      nblocks++;
      totalspace += slab->blockSize;
      freespace += slab->fullChunkSize * block->nfree;
      freechunks += block->nfree;
    }
  }

  if (printfunc)
  {
    char    stats_string[200];

    snprintf(stats_string, sizeof(stats_string),
         "%zu total in %zd blocks; %zu free (%zd chunks); %zu used",
         totalspace, nblocks, freespace, freechunks,
         totalspace - freespace);
    printfunc(context, passthru, stats_string);
  }

  if (totals)
  {
    totals->nblocks += nblocks;
    totals->freechunks += freechunks;
    totals->totalspace += totalspace;
    totals->freespace += freespace;
  }
}


#ifdef MEMORY_CONTEXT_CHECKING

/*
 * SlabCheck
 *    Walk through chunks and check consistency of memory.
 *
 * NOTE: report errors as WARNING, *not* ERROR or FATAL.  Otherwise you'll
 * find yourself in an infinite loop when trouble occurs, because this
 * routine will be entered again when elog cleanup tries to release memory!
 */
static void
SlabCheck(MemoryContext context)
{
  int     i;
  SlabContext *slab = castNode(SlabContext, context);
  const char *name = slab->header.name;
  char     *freechunks;

  Assert(slab);
  Assert(slab->chunksPerBlock > 0);

  /* bitmap of free chunks on a block */
  freechunks = palloc(slab->chunksPerBlock * sizeof(bool));

  /* walk all the freelists */
  for (i = 0; i <= slab->chunksPerBlock; i++)
  {
    int     j,
          nfree;
    dlist_iter  iter;

    /* walk all blocks on this freelist */
    dlist_foreach(iter, &slab->freelist[i])
    {
      int     idx;
      SlabBlock  *block = dlist_container(SlabBlock, node, iter.cur);

      /*
       * Make sure the number of free chunks (in the block header)
       * matches position in the freelist.
       */
      if (block->nfree != i)
        elog(WARNING, "problem in slab %s: number of free chunks %d in block %p does not match freelist %d",
           name, block->nfree, block, i);

      /* reset the bitmap of free chunks for this block */
      memset(freechunks, 0, (slab->chunksPerBlock * sizeof(bool)));
      idx = block->firstFreeChunk;

      /*
       * Now walk through the chunks, count the free ones and also
       * perform some additional checks for the used ones. As the chunk
       * freelist is stored within the chunks themselves, we have to
       * walk through the chunks and construct our own bitmap.
       */

      nfree = 0;
      while (idx < slab->chunksPerBlock)
      {
        SlabChunk  *chunk;

        /* count the chunk as free, add it to the bitmap */
        nfree++;
        freechunks[idx] = true;

        /* read index of the next free chunk */
        chunk = SlabBlockGetChunk(slab, block, idx);
        VALGRIND_MAKE_MEM_DEFINED(SlabChunkGetPointer(chunk), sizeof(int32));
        idx = *(int32 *) SlabChunkGetPointer(chunk);
      }

      for (j = 0; j < slab->chunksPerBlock; j++)
      {
        /* non-zero bit in the bitmap means chunk the chunk is used */
        if (!freechunks[j])
        {
          SlabChunk  *chunk = SlabBlockGetChunk(slab, block, j);

          /* chunks have both block and slab pointers, so check both */
          if (chunk->block != block)
            elog(WARNING, "problem in slab %s: bogus block link in block %p, chunk %p",
               name, block, chunk);

          if (chunk->slab != slab)
            elog(WARNING, "problem in slab %s: bogus slab link in block %p, chunk %p",
               name, block, chunk);

          /* there might be sentinel (thanks to alignment) */
          if (slab->chunkSize < (slab->fullChunkSize - sizeof(SlabChunk)))
            if (!sentinel_ok(chunk, slab->chunkSize))
              elog(WARNING, "problem in slab %s: detected write past chunk end in block %p, chunk %p",
                 name, block, chunk);
        }
      }

      /*
       * Make sure we got the expected number of free chunks (as tracked
       * in the block header).
       */
      if (nfree != block->nfree)
        elog(WARNING, "problem in slab %s: number of free chunks %d in block %p does not match bitmap %d",
           name, block->nfree, block, nfree);
    }
  }
}

#endif              /* MEMORY_CONTEXT_CHECKING */

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Created: 2022-03-09 17:30