Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 7 Feb 2022 10:07:54 +0100 | Subject | Re: [RFC PATCH] riscv: reduce THREAD_SIZE from 16KB to 8KB for RV64 |
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On Mon, Feb 7, 2022 at 9:38 AM Andreas Schwab <schwab@linux-m68k.org> wrote: > > On Feb 07 2022, David Abdurachmanov wrote: > > > On Sun, Feb 6, 2022 at 7:53 PM Jisheng Zhang <jszhang@kernel.org> wrote: > >> > >> After irq stack is supported, it's possible to use small THREAD_SIZE. > >> In fact, I tested this patch on a Lichee RV board, looks good so far. > > > > We went from 8K to 16K somewhere in mid-2020 on riscv64 because we > > were seeing some random crashes in various distributions (Debian, > > Fedora, OpenSUSE). Thus we matched what other popular arches do, i.e. > > 16K.
It sounds like 2020 predates both HAVE_ARCH_VMAP_STACK and IRQ stacks, so I would say that it was necessary back then because the crashes were too hard to debug, but it's worth trying again now at least as a compile-time option under CONFIG_EXPERT.
You need VMAP stacks to reliably get a backtrace out, and you need IRQ stacks to make overflows happen reproducibly (and less often).
> I think NFS is one of the worst offenders. I'm running an Unleashed > with NFS root, which probably amplifies this.
I think there are a few others that can be equally bad, and some of them might stack on top of others, such as swap over ecryptfs over nfs over an encrypted network tunnel over infiniband. In the end, you just need one badly written driver, or a compile bug to trigger it, and we have plenty of both.
Arnd
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