Re: [LSF/MM/BPF TOPIC] Dynamic Growth of Kernel Stacks

[Matthew Wilcox <willy@infradead.org>]

On Fri, Feb 23, 2024 at 01:49:08PM -0800, Peter Collingbourne wrote:
> I wonder if this is another potential use case for bringing back
> cleancache, as proposed in [1]? The idea would be that all kernel
> stacks have 16KB allocations but only one page accessible and the rest
> available as cleancache. We can handle a fault on one of those pages
> by discarding the cleancache page and remapping it as r/w.

That seems like the most complicated way to solve the problem.
Stack pages which have not been accessed contain no data, so do not
need swap or cleancache, they just need to be allocatable.  And the
fault handler needs to be able to handle faults from interrupt context,
which I'm not sure all architectures can do.

The "We need to be able to allocate memory from interrupt context" is
really not that hard to handle; just keep three pages in a per-cpu array.
Refill the array at return-to-process-context.