netdev - Re: [PATCH] netdevsim: fib: Make use of rhashtable

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Message-ID: <ZEjw7XXFro6zYYXz@gondor.apana.org.au>
Date:   Wed, 26 Apr 2023 17:37:49 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Cai Huoqing <cai.huoqing@...ux.dev>
Cc:     cai.huoqing@...ux.dev, kuba@...nel.org, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netdevsim: fib: Make use of rhashtable_iter

Cai Huoqing <cai.huoqing@...ux.dev> wrote:
> Iterating 'fib_rt_ht' by rhashtable_walk_next and rhashtable_iter directly
> instead of using list_for_each, because each entry of fib_rt_ht can be
> found by rhashtable API. And remove fib_rt_list.
> 
> Signed-off-by: Cai Huoqing <cai.huoqing@...ux.dev>
> ---
> drivers/net/netdevsim/fib.c | 37 ++++++++++++++++++-------------------
> 1 file changed, 18 insertions(+), 19 deletions(-)

What is the rationale for this patch? Are you trying to save
memory?

> @@ -1099,9 +1090,12 @@ static void nsim_fib_dump_inconsistent(struct notifier_block *nb)
>        /* The notifier block is still not registered, so we do not need to
>         * take any locks here.
>         */
> -       list_for_each_entry_safe(fib_rt, fib_rt_tmp, &data->fib_rt_list, list) {
> -               rhashtable_remove_fast(&data->fib_rt_ht, &fib_rt->ht_node,
> +       rhashtable_walk_enter(&data->fib_rt_ht, &hti);
> +       rhashtable_walk_start(&hti);
> +       while ((pos = rhashtable_walk_next(&hti))) {
> +               rhashtable_remove_fast(&data->fib_rt_ht, hti.p,
>                                       nsim_fib_rt_ht_params);
> +               fib_rt = rhashtable_walk_peek(&hti);
>                nsim_fib_rt_free(fib_rt, data);
>        }

In general rhashtable walks are not stable.  You may miss entries
or see entries twice.  They should be avoided unless absolutely
necessary.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt