[TECH TOPIC] Implementing malloc

[Matthew Wilcox <willy@infradead.org>]

malloc() is a standard part of the C library.  Yet we force new Linux
programmers to learn the difference between vmalloc(), kmalloc() and
kvmalloc().  They even have to acquire an understanding of the difference
between GFP_KERNEL and GFP_ATOMIC.  If they are particularly unlucky,
they may have to understand other combinations of GFP flags.

This topic proposes that we should implement malloc() and calloc().
Various options will be discussed, their increasing implementation
complexity corresponding to utility in a greater range of situations.
This will also benefit Rust as we can use the same infrastructure to
implement std::alloc.

We'll also discuss the semantics of corner cases (fallibility, zero
sized allocations, overflowing allocations and very large allocations)
as well as out-of-bounds and use-after-free detection.