nuttx/mm/mm_heap/mm_shrinkchunk.c

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/****************************************************************************
* mm/mm_heap/mm_shrinkchunk.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <assert.h>
#include <nuttx/mm/mm.h>
#include "mm_heap/mm.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: mm_shrinkchunk
*
* Description:
* Reduce the size of the chunk specified by the node structure to the
* specified size. this internal logic is used both from memalign to
* dispose of any trailing memory in the aligned allocation and also by
* realloc when there is a request to reduce the size of an allocation.
*
* NOTES:
* (1) size is the whole chunk size (payload and header)
* (2) the caller must hold the MM mutex.
*
****************************************************************************/
void mm_shrinkchunk(FAR struct mm_heap_s *heap,
FAR struct mm_allocnode_s *node, size_t size)
{
FAR struct mm_freenode_s *next;
DEBUGASSERT((size & MM_GRAN_MASK) == 0);
/* Get a reference to the next node */
next = (FAR struct mm_freenode_s *)((FAR char *)node + node->size);
/* Check if it is free */
if ((next->preceding & MM_ALLOC_BIT) == 0)
{
FAR struct mm_allocnode_s *andbeyond;
FAR struct mm_freenode_s *newnode;
/* Get the chunk next the next node (which could be the tail chunk) */
andbeyond = (FAR struct mm_allocnode_s *)
((FAR char *)next + next->size);
/* Remove the next node. There must be a predecessor, but there may
* not be a successor node.
*/
DEBUGASSERT(next->blink);
next->blink->flink = next->flink;
if (next->flink)
{
next->flink->blink = next->blink;
}
/* Create a new chunk that will hold both the next chunk and the
* tailing memory from the aligned chunk.
*/
newnode = (FAR struct mm_freenode_s *)((FAR char *)node + size);
/* Set up the size of the new node */
newnode->size = next->size + node->size - size;
newnode->preceding = size;
node->size = size;
andbeyond->preceding = newnode->size |
(andbeyond->preceding & MM_ALLOC_BIT);
/* Add the new node to the freenodelist */
mm_addfreechunk(heap, newnode);
}
/* The next chunk is allocated. Try to free the end portion at the end
* chunk to be shrunk.
*/
else if (node->size >= size + SIZEOF_MM_FREENODE)
{
FAR struct mm_freenode_s *newnode;
/* Create a new chunk that will hold both the next chunk and the
* tailing memory from the aligned chunk.
*/
newnode = (FAR struct mm_freenode_s *)((FAR char *)node + size);
/* Set up the size of the new node */
newnode->size = node->size - size;
newnode->preceding = size;
node->size = size;
next->preceding = newnode->size | MM_ALLOC_BIT;
/* Add the new node to the freenodelist */
mm_addfreechunk(heap, newnode);
}
}