On Thu, 14 Mar 2024 14:54:57 +0000 Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:
> CONFIG_DEBUG_STACK_USAGE provides a mechanism to determine the minimum
> amount of memory left in a stack. Every time a new low-memory record is
> reached, a message is printed to the console.
>
> However, this doesn't reveal how many pages within each stack were
> actually used. Introduce a mechanism that keeps count the number of
> times each of the stack's pages were reached:
>
> $ grep kstack /proc/vmstat
> kstack_page_1 19974
> kstack_page_2 94
> kstack_page_3 0
> kstack_page_4 0
>
> In the above example, out of 20,068 threads that exited on this
> machine, only 94 reached the second page of their stack, and none
> touched pages three or four.
>
> In fleet environments with millions of machines, this data can help
> optimize kernel stack sizes.
We really should have somewhere to document vmstat things.
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -153,10 +153,39 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> VMA_LOCK_ABORT,
> VMA_LOCK_RETRY,
> VMA_LOCK_MISS,
> +#endif
> +#ifdef CONFIG_DEBUG_STACK_USAGE
> + KSTACK_PAGE_1,
> + KSTACK_PAGE_2,
> +#if THREAD_SIZE >= (4 * PAGE_SIZE)
> + KSTACK_PAGE_3,
> + KSTACK_PAGE_4,
> +#endif
> +#if THREAD_SIZE > (4 * PAGE_SIZE)
> + KSTACK_PAGE_REST,
> +#endif
> #endif
> NR_VM_EVENT_ITEMS
> };
This seems a rather cumbersome way to produce a kind of histogram. I
wonder if there should be a separate pseudo file for this.
And there may be a call for extending this. For example I can forsee
people wanting to know "hey, which process did that", in which case
we'll want to record additional info.
