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Comment:Use an allocation count and freelist instead of a membership bitfield in the mini lookaside allocator
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SHA3-256: 9496b4d378ed38a8d37b2b5f3d575f17b1d19e1890c3ec3b1d409fbe7026fb89
User & Date: numist 2019-10-18 22:54:54
Context
2019-10-18
22:54
Use an allocation count and freelist instead of a membership bitfield in the mini lookaside allocator Leaf check-in: 9496b4d3 user: numist tags: 2-size-lookaside
2019-10-09
17:38
Merge recent fixes and enhancements from trunk. check-in: 553258c2 user: drh tags: 2-size-lookaside
Changes
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Changes to src/lookaside.c. 

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    pLookaside->pInit = pLookaside->pFree;
    pLookaside->pFree = 0;
  }
}

#ifndef SQLITE_OMIT_LOOKASIDE

static void *lookasideSlotAlloc(Lookaside *pLookaside, u64 n){
  LookasideSlot *pBuf;
  if( (pBuf = pLookaside->pFree)!=0 ){
    pLookaside->pFree = pBuf->pNext;
    pLookaside->anStat[0]++;
    return (void*)pBuf;
  }else if( (pBuf = pLookaside->pInit)!=0 ){
    pLookaside->pInit = pBuf->pNext;
................................................................................
}

# ifndef SQLITE_OMIT_MINI_LOOKASIDE
#  ifndef SQLITE_MINI_LOOKASIDE_MIN_SLOT_SIZE
#   define SQLITE_MINI_LOOKASIDE_MIN_SLOT_SIZE 128
#  endif

static void *miniLookasideAlloc(Lookaside *pLookaside, u16 n){
  void *p = 0;
  LookasideSlot *pSlot;
  int iMiniSlot;
  
  assert( n<=pLookaside->szMini );
  
  if( !pLookaside->pMini ){
    pSlot = lookasideSlotAlloc(pLookaside, pLookaside->szTrue);
    if( !pSlot ){
      return p;
    }
    bzero(pSlot, sizeof(LookasideSlot));
    pLookaside->pMini = pSlot;
  }else{
    pSlot = pLookaside->pMini;
    assert( pSlot->bMembership );
  }
  
  assert( pSlot->bMembership < (1<<pLookaside->nMini)-1 );

  iMiniSlot = __builtin_ffs(~pSlot->bMembership) - 1;



  assert(iMiniSlot < pLookaside->nMini);
  assert( (pSlot->bMembership&(1<<iMiniSlot))==0 );
  pSlot->bMembership |= 1<<iMiniSlot;


  p = (char *)pSlot + sizeof(LookasideSlot) + (pLookaside->szMini * iMiniSlot);

  /* Remove slot from pMini if it is full of sub-allocations */
  if( pSlot->bMembership == (1<<pLookaside->nMini)-1 ){

    /* Slot is full, dequeue from list */
    if( pSlot->pNext ){
      assert( pSlot->pNext->pPrev == pSlot );
      pSlot->pNext->pPrev = pSlot->pPrev;
    }
    if( pSlot->pPrev ){
      assert( pSlot->pPrev->pNext == pSlot );
................................................................................
      pSlot->pPrev->pNext = pSlot->pNext;
    }else{
      assert( pLookaside->pMini == pSlot );
      pLookaside->pMini = pSlot->pNext;
    }
    pSlot->pNext = pSlot->pPrev = 0;
  }
  return p;
}

static void miniLookasideFree(Lookaside *pLookaside, void *p){
  int iSlotNum = ((u8*)p - (u8*)pLookaside->pStart) / pLookaside->szTrue;
  LookasideSlot *pSlot = (LookasideSlot *)(iSlotNum * pLookaside->szTrue + (u8*)pLookaside->pStart);
  int iMiniSlot = ((u8*)p - ((u8*)pSlot + sizeof(LookasideSlot))) / pLookaside->szMini;
  
  assert( pSlot->bMembership );
  assert( pSlot->bMembership < (1<<pLookaside->nMini) );
  assert( iMiniSlot<pLookaside->nMini );
  
  /* Return slot to pMini list if it was full */
  if( pSlot->bMembership == (1<<pLookaside->nMini)-1 ){
    assert( pSlot->pNext == pSlot->pPrev && pSlot->pPrev == 0 );
    if( pLookaside->pMini ){
      assert( !pLookaside->pMini->pPrev );
      pSlot->pNext = pLookaside->pMini;
      pSlot->pNext->pPrev = pSlot;
    }
    pLookaside->pMini = pSlot;
  }
  
  pSlot->bMembership &= ~(1<<iMiniSlot);
#ifdef SQLITE_DEBUG
  memset(p, 0xaa, pLookaside->szMini);
#endif



  
  /* Return slot to the lookaside pool if it is empty */
  if( pSlot->bMembership == 0 ){
    if( pSlot->pNext ){
      assert( pSlot->pNext->pPrev == pSlot );
      pSlot->pNext->pPrev = pSlot->pPrev;
    }
    if( pSlot->pPrev ){
      assert( pSlot->pPrev->pNext == pSlot );
      pSlot->pPrev->pNext = pSlot->pNext;
................................................................................
      pLookaside->pMini = pSlot->pNext;
    }
    lookasideSlotFree(pLookaside, pSlot);
  }
}

# else
#  define miniLookasideAlloc(A, B) lookasideSlotAlloc(A, B)
#  define miniLookasideFree(A, B) lookasideSlowFree(A, B)
# endif /* !SQLITE_OMIT_MINI_LOOKASIDE */

int sqlite3LookasideOpen(void *pBuf, int sz, int cnt, Lookaside *pLookaside){
  void *pStart;

  if( sqlite3LookasideUsed(pLookaside,0)>0 ){
    return SQLITE_BUSY;
................................................................................
  if( n>pLookaside->sz ){
    if( !pLookaside->bDisable ){
      pLookaside->anStat[1]++;
    }
    return 0;
  }
  if( n<=pLookaside->szMini && pLookaside->nMini > 1 ){
    return miniLookasideAlloc(pLookaside, n);
  }
  return lookasideSlotAlloc(pLookaside, n);
}

/*
** Free memory previously obtained from sqlite3LookasideAlloc().
*/
void sqlite3LookasideFree(Lookaside *pLookaside, void *p){
  assert( sqlite3IsLookaside(pLookaside, p) );








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    pLookaside->pInit = pLookaside->pFree;
    pLookaside->pFree = 0;
  }
}

#ifndef SQLITE_OMIT_LOOKASIDE

static void *lookasideSlotAlloc(Lookaside *pLookaside){
  LookasideSlot *pBuf;
  if( (pBuf = pLookaside->pFree)!=0 ){
    pLookaside->pFree = pBuf->pNext;
    pLookaside->anStat[0]++;
    return (void*)pBuf;
  }else if( (pBuf = pLookaside->pInit)!=0 ){
    pLookaside->pInit = pBuf->pNext;
................................................................................
}

# ifndef SQLITE_OMIT_MINI_LOOKASIDE
#  ifndef SQLITE_MINI_LOOKASIDE_MIN_SLOT_SIZE
#   define SQLITE_MINI_LOOKASIDE_MIN_SLOT_SIZE 128
#  endif

static void *miniLookasideAlloc(Lookaside *pLookaside){
  LookasideSlot *pMiniSlot;
  LookasideSlot *pSlot;
  int iMiniSlot;
  


  if( !pLookaside->pMini ){
    pSlot = lookasideSlotAlloc(pLookaside);
    if( !pSlot ){
      return 0;
    }
    bzero(pSlot, sizeof(LookasideSlot));
    pLookaside->pMini = pSlot;
  }else{
    pSlot = pLookaside->pMini;
    assert( pSlot->nAlloc );
  }
  
  assert( pSlot->nAlloc < pLookaside->nMini );

  if( (pMiniSlot = pSlot->pFree) ){
    pSlot->pFree = pMiniSlot->pNext;
  }else{
    iMiniSlot = pSlot->nAlloc;
    assert(iMiniSlot < pLookaside->nMini);


    pMiniSlot = (LookasideSlot *)((char *)pSlot + sizeof(LookasideSlot) + (pLookaside->szMini * iMiniSlot));
  }


  /* Remove slot from pMini if it is full of sub-allocations */

  if( ++(pSlot->nAlloc) == pLookaside->nMini ){
    /* Slot is full, dequeue from list */
    if( pSlot->pNext ){
      assert( pSlot->pNext->pPrev == pSlot );
      pSlot->pNext->pPrev = pSlot->pPrev;
    }
    if( pSlot->pPrev ){
      assert( pSlot->pPrev->pNext == pSlot );
................................................................................
      pSlot->pPrev->pNext = pSlot->pNext;
    }else{
      assert( pLookaside->pMini == pSlot );
      pLookaside->pMini = pSlot->pNext;
    }
    pSlot->pNext = pSlot->pPrev = 0;
  }
  return pMiniSlot;
}

static void miniLookasideFree(Lookaside *pLookaside, void *p){
  int iSlotNum = ((u8*)p - (u8*)pLookaside->pStart) / pLookaside->szTrue;
  LookasideSlot *pSlot = (LookasideSlot *)(iSlotNum * pLookaside->szTrue + (u8*)pLookaside->pStart);
  LookasideSlot *pMiniSlot = (LookasideSlot *)p;
  
  assert( pSlot->nAlloc );
  assert( pSlot->nAlloc <= pLookaside->nMini );
  assert( iMiniSlot<pLookaside->nMini );
  
  /* Return slot to pMini list if it was full */
  if( pSlot->nAlloc==pLookaside->nMini ){
    assert( pSlot->pNext == pSlot->pPrev && pSlot->pPrev == 0 );
    if( pLookaside->pMini ){
      assert( !pLookaside->pMini->pPrev );
      pSlot->pNext = pLookaside->pMini;
      pSlot->pNext->pPrev = pSlot;
    }
    pLookaside->pMini = pSlot;
  }
  

#ifdef SQLITE_DEBUG
  memset(p, 0xaa, pLookaside->szMini);
#endif
  pSlot->nAlloc--;
  pMiniSlot->pNext = pSlot->pFree;
  pSlot->pFree = pMiniSlot;

  /* Return slot to the lookaside pool if it is empty */
  if( pSlot->nAlloc == 0 ){
    if( pSlot->pNext ){
      assert( pSlot->pNext->pPrev == pSlot );
      pSlot->pNext->pPrev = pSlot->pPrev;
    }
    if( pSlot->pPrev ){
      assert( pSlot->pPrev->pNext == pSlot );
      pSlot->pPrev->pNext = pSlot->pNext;
................................................................................
      pLookaside->pMini = pSlot->pNext;
    }
    lookasideSlotFree(pLookaside, pSlot);
  }
}

# else
#  define miniLookasideAlloc(A) lookasideSlotAlloc(A)
#  define miniLookasideFree(A, B) lookasideSlotFree(A, B)
# endif /* !SQLITE_OMIT_MINI_LOOKASIDE */

int sqlite3LookasideOpen(void *pBuf, int sz, int cnt, Lookaside *pLookaside){
  void *pStart;

  if( sqlite3LookasideUsed(pLookaside,0)>0 ){
    return SQLITE_BUSY;
................................................................................
  if( n>pLookaside->sz ){
    if( !pLookaside->bDisable ){
      pLookaside->anStat[1]++;
    }
    return 0;
  }
  if( n<=pLookaside->szMini && pLookaside->nMini > 1 ){
    return miniLookasideAlloc(pLookaside);
  }
  return lookasideSlotAlloc(pLookaside);
}

/*
** Free memory previously obtained from sqlite3LookasideAlloc().
*/
void sqlite3LookasideFree(Lookaside *pLookaside, void *p){
  assert( sqlite3IsLookaside(pLookaside, p) );

Changes to src/sqliteInt.h. 

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#endif /* SQLITE_OMIT_MINILOOKASIDE */
};
struct LookasideSlot {
  LookasideSlot *pNext;    /* Next buffer in the list of buffers */
#ifndef SQLITE_OMIT_MINILOOKASIDE
  /* The members below are only valid for slots inside the mini-allocator */
  LookasideSlot *pPrev;    /* Previous partially-used buffer in the list */
  int bMembership;         /* Bitfield tracking sub-allocations within slot */

#endif /* SQLITE_OMIT_MINILOOKASIDE */
};

#define DisableLookaside  db->lookaside.bDisable++;db->lookaside.sz=0
#define EnableLookaside   db->lookaside.bDisable--;\
   db->lookaside.sz=db->lookaside.bDisable?0:db->lookaside.szTrue









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#endif /* SQLITE_OMIT_MINILOOKASIDE */
};
struct LookasideSlot {
  LookasideSlot *pNext;    /* Next buffer in the list of buffers */
#ifndef SQLITE_OMIT_MINILOOKASIDE
  /* The members below are only valid for slots inside the mini-allocator */
  LookasideSlot *pPrev;    /* Previous partially-used buffer in the list */
  u16 nAlloc;              /* Number of sub-allocations ever returned from this slot */
  LookasideSlot *pFree;    /* List of freed sub-allocations */
#endif /* SQLITE_OMIT_MINILOOKASIDE */
};

#define DisableLookaside  db->lookaside.bDisable++;db->lookaside.sz=0
#define EnableLookaside   db->lookaside.bDisable--;\
   db->lookaside.sz=db->lookaside.bDisable?0:db->lookaside.szTrue

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