When I was working on a hobby kernel, I'll confess I just took dlmalloc and called it a day. There are loads of interesting problems in kernel development (mapping pages, doing crazy stuff in page fault handlers, synchronization, filesystems) but somehow I didn't find malloc to be one of them. I guess anyone reasonably skilled at C can write a bad malloc pretty quickly, and once you get to that point you don't really learn that much by putting more effort into it.
There's a huge depth to a good malloc() implementation. While you're wise to avoid it when your interests are focused on kernel development, I'd recommend every programmer to have a go at writing malloc/free one day. Avoiding terrible performance problems is pretty tricky. At the very least, you'll gain a lot of respect for memory allocation and will discover that there's a lot of work going on behind the scenes when your code tries to allocate only a few bytes of memory.
Yup, malloc is usually a homework assignment in the upper-level CS classes in my university. I wrote it then (and again for my friends' hobby kernel) but I couldn't do it now.
