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

[Michal Hocko <mhocko@suse.com>]

Hi Pasha,
is this something you still do consider interesting (and also productive
in absence of x86 maintainers) to discuss at LSFMM?

On Thu 22-02-24 20:03:37, Pavel Tatashin wrote:
> For a long time, an 8K kernel stack was large enough. However, since
> 2014, the default stack size has increased to 16K [1]. To conserve
> memory at Google, we maintained 8K stacks via a custom patch while
> verifying that our workload could fit within this limit.
> 
> As we qualify new workloads and kernels, we find it more difficult to
> keep the stacks at 8K. Therefore, we will increase the stack size to
> the mainline value of 16K. However, this translates to a significant
> increase in memory usage, potentially counted in petabytes.
> 
> With virtually mapped stacks [2], it's possible to implement
> auto-growth on faults. Ideally, the vast majority of kernel threads
> could fit into 4K or 8K stacks, with only a small number requiring
> deeper stacks that would expand as needed.
> 
> The complication is that new pages must always be available from
> within an interrupt context. To ensure this, pages must be accessible
> to kernel threads in an atomic and lockless manner. This could be
> achieved by using a per-CPU supply of pages dedicated to handling
> kernel-stack faults.
> 
> [1] https://lwn.net/Articles/600644
> [2] https://lwn.net/Articles/692608
> _______________________________________________
> Lsf-pc mailing list
> Lsf-pc@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/lsf-pc

-- 
Michal Hocko
SUSE Labs