Re: [TECH TOPIC] Implementing malloc

[Matthew Wilcox <willy@infradead.org>]

On Mon, Jun 29, 2026 at 09:48:25AM -0700, H. Peter Anvin wrote:
> On 2026-06-29 07:29, Matthew Wilcox wrote:
> > 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.
> 
> You *NEED* to understand that if you are going to program kernel code. There
> probably isn't anything more important, *really*.

There's a lot of kernel code where that's true.  malloc() is not The One
True Interface to allocate memory, and at this point I'm not advocating
for removing any of the existing ones.

But we do have code which just needs to allocate "some memory", doesn't
have any particularly weird restrictions, and where usability is more
important than "pedal to the metal".  An example might be something
like zlib.  It needs to allocate some temporary memory, and why have to

#ifdef __KERNEL__
#define malloc(x)	kvmalloc(x, GFP_KERNEL)
#endif

> The kernel is a memory manager first, a scheduler second, all else is commentary.

Some filesystem people might have things to say about that.  But
increasingly the kernel is just the runtime for eBPF programs ;-)