xiaoxiang781216 commented on code in PR #5991:
URL: https://github.com/apache/incubator-nuttx/pull/5991#discussion_r844869056
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mm/mm_heap/mm_initialize.c:
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@@ -93,12 +93,17 @@ void mm_addregion(FAR struct mm_heap_s *heap, FAR void
*heapstart,
DEBUGVERIFY(mm_takesemaphore(heap));
- /* Adjust the provided heap start and size so that they are both aligned
- * with the MM_MIN_CHUNK size.
+ /* Adjust the provided heap start and size.
+ *
+ * Note: (uintptr_t)node + SIZEOF_MM_ALLOCNODE is what's actually
+ * returned to the malloc user, which should have natural alignment.
+ * (that is, in this implementation, MM_MIN_CHUNK-alignment.)
*/
- heapbase = MM_ALIGN_UP((uintptr_t)heapstart);
- heapend = MM_ALIGN_DOWN((uintptr_t)heapstart + (uintptr_t)heapsize);
+ heapbase = MM_ALIGN_UP((uintptr_t)heapstart + SIZEOF_MM_ALLOCNODE)
+ - SIZEOF_MM_ALLOCNODE;
+ heapend = MM_ALIGN_DOWN((uintptr_t)heapstart + (uintptr_t)heapsize)
Review Comment:
The original code:
1. Align heapbase and heapend to MM_MIN_CHUNK
2. #5906 ensure two preallocate nodes with MM_MIN_CHUNK
So, the rest of free slot should multiple of MM_MIN_CHUNK. It's strange that
we need an additional alignment here.
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