Oct 9, 2008 - is to start bookkeeping about which areas of physical memory are available for use and which are to be considered "occupied". The free space ...
Memory Allocation From OSDev Wiki This page is about the allocation of memory from memory that is already available to the process (like malloc() and new()). For the allocation of page frames see Page Frame Allocation. One of the most basic functions of a kernel is the memory management, i.e. the allocating and freeing of memory. At square one, the kernel is the only process in the system. But it is not alone: BIOS data structures, memory-mapped hardware registers etc. populate the address space. Among the first things a kernel must do is to start bookkeeping about which areas of physical memory are available for use and which are to be considered "occupied". The free space will subsequently be used for kernel data structures, application binaries, their heap and stack etc. - the kernel needs a function that marks a memory area as reserved, and makes that memory available to the process requiring it. In the C Standard Library, this is handled by malloc() and free(); in C++ by new() and delete().
Contents 1 A very very simple Memory Manager 2 Tips to go further 3 Memory & Microkernels 4 See Also 4.1 Tutorials 4.2 External Links
A very very simple Memory Manager The easiest you can do is the WaterMark allocator. Just keep track of how far you've allocated and forget about the notion of "freeing". before ... +----+-----+--+--------//--+ |##A#|##B##|C#| free | +----+-----+--+---------//-+ ^freebase ^freetop
When allocating N bytes for D, simply check that freetop-freebase>N and increment freebase by N. Period. A very simple Memory Manager Now, if you need to free things, one of the easiest solution is to put at the start of the freed zone a descriptor that allows you to insert it in a list of free zones. Keeping that list sorted by address helps you identifying contiguous free zones and allows you to merge them in larger free zones.
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Memory Allocation - OSDev Wiki
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first free \/ +----+-----+--+----+---+-----//--+ |##A#|free |C#|free|#E#| free | +----+-|---+--+-|--+---+-----//--+ +-next>--+
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