* Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote:
> PAGE_SIZE is not guaranteed to be equal to or less than 8 times the
> THREAD_SIZE.
>
> E.g. architecture hexagon may have page size 1M and thread size 4096.
> This would lead to a division by zero in the calculation of max_threads.
>
> With 32-bit calculation there is no solution which delivers valid results
> for all possible combinations of the parameters.
> The code is only called once.
> Hence a 64-bit calculation can be used as solution.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> ---
> kernel/fork.c | 35 ++++++++++++++++++++++++++---------
> 1 file changed, 26 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index bf1ff00..69ff08f 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -88,6 +88,16 @@
> #include <trace/events/task.h>
>
> /*
> + * Minimum number of threads to boot the kernel
> + */
> +#define MIN_THREADS 20
> +
> +/*
> + * Maximum number of threads
> + */
> +#define MAX_THREADS FUTEX_TID_MASK
> +
> +/*
> * Protected counters by write_lock_irq(&tasklist_lock)
> */
> unsigned long total_forks; /* Handle normal Linux uptimes. */
> @@ -258,18 +268,25 @@ void __init __weak arch_task_cache_init(void) { }
> */
> static void set_max_threads(void)
> {
> - /*
> - * The default maximum number of threads is set to a safe
> - * value: the thread structures can take up at most half
> - * of memory.
> - */
> - max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE);
> + u64 threads;
>
> /*
> - * we need to allow at least 20 threads to boot a system
> + * The number of threads shall be limited such that the thread
> + * structures may only consume a small part of the available memory.
> */
> - if (max_threads < 20)
> - max_threads = 20;
> + if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
> + threads = MAX_THREADS;
> + else
> + threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
> + (u64) THREAD_SIZE * 8UL);
> +
> + if (threads > MAX_THREADS)
> + threads = MAX_THREADS;
> +
> + if (threads < MIN_THREADS)
> + threads = MIN_THREADS;
> +
> + max_threads = (int) threads;
> }
So why does this patch do two things:
- parametrizes set_max_threads() via defines
- fixes a bug
?
Those two things should be done in two separate patches, first the
introduction of parameters, then the fixing of the bug.
I suggested this in my first review: separate out and keep the fix
portion of the series minimal.
Thanks,
Ingo
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