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Commit543852f

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Allocate freechunks bitmap as part of SlabContext
The bitmap used by SlabCheck to cross-check free chunks in a block usedto be allocated for each SlabCheck call, and was never freed. The memoryleak could be fixed by simply adding a pfree call, but it's actually abad idea to do any allocations in SlabCheck at all as it assumes thestate of the memory management as a whole is sane.So instead we allocate the bitmap as part of SlabContext, which meanswe don't need to do any allocations in SlabCheck and the bitmap goesaway together with the SlabContext.Backpatch to 10, where the Slab context was introduced.Author: Tomas VondraReported-by: Andres FreundReviewed-by: Tom LaneBackpatch-through: 10Discussion:https://www.postgresql.org/message-id/20200116044119.g45f7pmgz4jmodxj%40alap3.anarazel.de
1 parent4b0e0f6 commit543852f

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‎src/backend/utils/mmgr/slab.c

Lines changed: 21 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -70,6 +70,9 @@ typedef struct SlabContext
7070
intchunksPerBlock;/* number of chunks per block */
7171
intminFreeChunks;/* min number of free chunks in any block */
7272
intnblocks;/* number of blocks allocated */
73+
#ifdefMEMORY_CONTEXT_CHECKING
74+
bool*freechunks;/* bitmap of free chunks in a block */
75+
#endif
7376
/* blocks with free space, grouped by number of free chunks: */
7477
dlist_headfreelist[FLEXIBLE_ARRAY_MEMBER];
7578
}SlabContext;
@@ -229,6 +232,15 @@ SlabContextCreate(MemoryContext parent,
229232
/* Size of the memory context header */
230233
headerSize= offsetof(SlabContext,freelist)+freelistSize;
231234

235+
#ifdefMEMORY_CONTEXT_CHECKING
236+
/*
237+
* With memory checking, we need to allocate extra space for the bitmap
238+
* of free chunks. The bitmap is an array of bools, so we don't need to
239+
* worry about alignment.
240+
*/
241+
headerSize+=chunksPerBlock*sizeof(bool);
242+
#endif
243+
232244
slab= (SlabContext*)malloc(headerSize);
233245
if (slab==NULL)
234246
{
@@ -258,6 +270,12 @@ SlabContextCreate(MemoryContext parent,
258270
for (i=0;i< (slab->chunksPerBlock+1);i++)
259271
dlist_init(&slab->freelist[i]);
260272

273+
#ifdefMEMORY_CONTEXT_CHECKING
274+
/* set the freechunks pointer right after the freelists array */
275+
slab->freechunks
276+
= (bool*)slab+ offsetof(SlabContext,freelist)+freelistSize;
277+
#endif
278+
261279
/* Finally, do the type-independent part of context creation */
262280
MemoryContextCreate((MemoryContext)slab,
263281
T_SlabContext,
@@ -701,14 +719,10 @@ SlabCheck(MemoryContext context)
701719
inti;
702720
SlabContext*slab=castNode(SlabContext,context);
703721
constchar*name=slab->header.name;
704-
char*freechunks;
705722

706723
Assert(slab);
707724
Assert(slab->chunksPerBlock>0);
708725

709-
/* bitmap of free chunks on a block */
710-
freechunks=palloc(slab->chunksPerBlock*sizeof(bool));
711-
712726
/* walk all the freelists */
713727
for (i=0;i <=slab->chunksPerBlock;i++)
714728
{
@@ -731,7 +745,7 @@ SlabCheck(MemoryContext context)
731745
name,block->nfree,block,i);
732746

733747
/* reset the bitmap of free chunks for this block */
734-
memset(freechunks,0, (slab->chunksPerBlock*sizeof(bool)));
748+
memset(slab->freechunks,0, (slab->chunksPerBlock*sizeof(bool)));
735749
idx=block->firstFreeChunk;
736750

737751
/*
@@ -748,7 +762,7 @@ SlabCheck(MemoryContext context)
748762

749763
/* count the chunk as free, add it to the bitmap */
750764
nfree++;
751-
freechunks[idx]= true;
765+
slab->freechunks[idx]= true;
752766

753767
/* read index of the next free chunk */
754768
chunk=SlabBlockGetChunk(slab,block,idx);
@@ -759,7 +773,7 @@ SlabCheck(MemoryContext context)
759773
for (j=0;j<slab->chunksPerBlock;j++)
760774
{
761775
/* non-zero bit in the bitmap means chunk the chunk is used */
762-
if (!freechunks[j])
776+
if (!slab->freechunks[j])
763777
{
764778
SlabChunk*chunk=SlabBlockGetChunk(slab,block,j);
765779

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