OSSP CVS Repository

Ticket 63: Fragmentation of memory could be avoided by merging with spare block

This simple fix in mm_insert_chunk allows to avoid memory fragmentation which can cause allocation failures:

---

static void mm_insert_chunk(MM mm, mem_chunk *mcInsert)
{

mem_chunk *mc;
mem_chunk *mcPrev,*mcPrevPrev;
mem_chunk *mcNext;
if (!mm_core_lock((void *)mm, MM_LOCK_RW))

return;

mcPrevPrev = mc = &(mm->mp_freechunks);
while (mc->mc_u.mc_next != NULL && (char *)(mc->mc_u.mc_next) <(char *)mcInsert) {

mcPrevPrev = mc;
mc = mc->mc_u.mc_next;

}
mcPrev = mc;
mcNext = mc->mc_u.mc_next;
if (mcPrev == mcInsert || mcNext == mcInsert) {

mm_core_unlock((void *)mm);
ERR(MM_ERR_ALLOC, "chunk of memory already in free list");
return;

}
if ((char *)mcPrev+(mcPrev->mc_size) == (char *)mcInsert && (mcNext != NULL && (char *)mcInsert+(mcInsert->mc_size) == (char *)mcNext)) {

/ merge with previous and next chunk /
mcPrev->mc_size += mcInsert->mc_size + mcNext->mc_size;
mcPrev->mc_u.mc_next = mcNext->mc_u.mc_next;
mm->mp_freechunks.mc_usize -= 1;

}
else if ((char *)mcPrev+(mcPrev->mc_size) == (char *)mcInsert) {

if ((char *)mcInsert+(mcInsert->mc_size) == (mm->mp_offset + (char *)mm)) {

/ merge with previous and spare block to decrease fragmentation /
mcPrevPrev->mc_u.mc_next = mcPrev->mc_u.mc_next;
mm->mp_offset -= (mcInsert->mc_size + mcPrev->mc_size);
mm->mp_freechunks.mc_usize -= 1;

}
else {

/ merge with previous chunk /
mcPrev->mc_size += mcInsert->mc_size;

}

}
else if (mcNext != NULL && (char *)mcInsert+(mcInsert->mc_size) == (char *)mcNext) {

/ merge with next chunk /
mcInsert->mc_size += mcNext->mc_size;
mcInsert->mc_u.mc_next = mcNext->mc_u.mc_next;
mcPrev->mc_u.mc_next = mcInsert;

}
else {

if ((char *)mcInsert+(mcInsert->mc_size) == (mm->mp_offset + (char *)mm)) {

/ merge with spare block to decrease fragmentation /
mm->mp_offset -= mcInsert->mc_size;

}
else {

/ no merging possible, so insert as new chunk */
mcInsert->mc_u.mc_next = mcNext;
mcPrev->mc_u.mc_next = mcInsert;
mm->mp_freechunks.mc_usize += 1;

}

}
mm_core_unlock((void *)mm);
return;
}

[Append remarks]

Remarks:

Now taken over into OSSP mm 1.4.0 in a slightly reformatted way. Thanks.

[Append remarks]

Properties:

Type:	new		Version:	1.3.1
Status:	fixed		Created:	2005-Aug-26 01:46
Severity:	3		Last Change:	2005-Sep-02 22:11
Priority:	4		Subsystem:	mm
Assigned To:	rse		Derived From:
Creator:	anonymous

Related Check-ins:

2005-Sep-02 21:50

•

Check-in [5166]: Optimize insertion of free memory chunks by merging with the spare area if possible to decrease memory fragmentation. (By rse)