Re: [PATCH] nano malloc allocator algorithm improvement

Keith Packard via Newlib <[email protected]> Sat, 22 Aug 2020 17:12:00 -0700

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

Keith Packard via Newlib <[email protected]> writes:

> Maarten van der Schrieck | Things Connected <[email protected]>
> writes:
>
>> The current nano malloc implementation has two issues reducing the amount of memory available and increasing fragmentation.
>>
>> The first issue is that sbrk() will be called to allocate a space with
>> the size of the entire requested alloc_size, even if the last free
>> chunk borders the edge of currently allocated memory. This means that
>> in a system with 20 kb of RAM, you will get ENOMEM when performing
>> this:
>
> Oh, that's a great idea. I did the same for realloc when the block was
> at the end of the heap; doing the same for malloc is a nice
> addition.

I've gone ahead and added this. Because this code is shared with
realloc, the overall impact on the code size is pretty modest. I think
it's easily worth the increase in code size because it will use ram more
efficiently now.

I can back-port this code to newlib if people are interested; certainly
having people on this list review the could would be great.

https://github.com/picolibc/picolibc/blob/main/newlib/libc/stdlib/nano-mallocr.c

-- 
-keith

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