Re: [PATCH] rss_stat: Add support to detect RSS updates of external mm

[Petr Mladek <pmladek@suse.com>]

On Tue 2019-11-05 21:44:51, Joel Fernandes (Google) wrote:
> Also vsprintf.c is refactored a bit to allow reuse of hashing code.

I agree with Sergey that it would make sense to move this outside
vsprintf.c.

> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index dee8fc467fcf..401baaac1813 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -761,11 +761,34 @@ static int __init initialize_ptr_random(void)
>  early_initcall(initialize_ptr_random);
>  
>  /* Maps a pointer to a 32 bit unique identifier. */
> +int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
> +{
> +	const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";

str is unused.

> +	unsigned long hashval;

IMHO, this local variable unnecessarily complicates the code.
I would use the pointer directly and let compiler to optimize.

> +	if (static_branch_unlikely(&not_filled_random_ptr_key))
> +		return -EAGAIN;
> +
> +#ifdef CONFIG_64BIT
> +	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
> +	/*
> +	 * Mask off the first 32 bits, this makes explicit that we have
> +	 * modified the address (and 32 bits is plenty for a unique ID).
> +	 */
> +	hashval = hashval & 0xffffffff;
> +#else
> +	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
> +#endif
> +	*hashval_out = hashval;
> +	return 0;
> +}

Best Regards,
Petr