linux-kernel - Re: [PATCH v13 9/9] lib/nodemask: Optimize node_random for nodemask with single NUMA node

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 09 Aug 2022 11:13:54 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v13 9/9] lib/nodemask: Optimize node_random for nodemask
 with single NUMA node

"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:

> The most common case for certain node_random usage (demotion nodemask) is with
> nodemask weight 1. We can avoid calling get_random_init() in that case and
> always return the only node set in the nodemask.

I think that this patch can sit between [5/9] and [6/9], just after it
is used.

> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> ---
>  lib/nodemask.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/lib/nodemask.c b/lib/nodemask.c
> index e22647f5181b..c91a6b0404a5 100644
> --- a/lib/nodemask.c
> +++ b/lib/nodemask.c
> @@ -20,12 +20,21 @@ EXPORT_SYMBOL(__next_node_in);
>   */
>  int node_random(const nodemask_t *maskp)
>  {
> -	int w, bit = NUMA_NO_NODE;
> +	int w, bit;
>  
>  	w = nodes_weight(*maskp);
> -	if (w)
> +	switch (w) {
> +	case 0:
> +		bit = NUMA_NO_NODE;
> +		break;
> +	case 1:
> +		bit = __first_node(maskp);

Per my understanding, first_node() is the formal API and we should use
that?  Just like we use nodes_weight() instead of __nodes_weight().

Best Regards,
Huang, Ying

> +		break;
> +	default:
>  		bit = bitmap_ord_to_pos(maskp->bits,
> -			get_random_int() % w, MAX_NUMNODES);
> +					get_random_int() % w, MAX_NUMNODES);
> +		break;
> +	}
>  	return bit;
>  }
>  #endif