netdev - Re: [PATCH net-next 2/2] net: openvswitch: make masks cache size configurable

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Message-ID: <20200723101556.GE23458@breakpoint.cc>
Date:   Thu, 23 Jul 2020 12:15:56 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eelco Chaudron <echaudro@...hat.com>
Cc:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
        davem@...emloft.net, dev@...nvswitch.org, kuba@...nel.org,
        pabeni@...hat.com, pshelar@....org
Subject: Re: [PATCH net-next 2/2] net: openvswitch: make masks cache size
 configurable

Eelco Chaudron <echaudro@...hat.com> wrote:
> On 22 Jul 2020, at 21:22, Florian Westphal wrote:
> > I see a 0 cache size is legal (turns it off) and that the allocation
> > path has a few sanity checks as well.
> > 
> > Would it make sense to add min/max policy to datapath_policy[] for this
> > as well?
> 
> Yes I could add the following:
> 
> @@ -1906,7 +1906,8 @@ static const struct nla_policy
> datapath_policy[OVS_DP_ATTR_MAX + 1] = {
>         [OVS_DP_ATTR_NAME] = { .type = NLA_NUL_STRING, .len = IFNAMSIZ - 1
> },
>         [OVS_DP_ATTR_UPCALL_PID] = { .type = NLA_U32 },
>         [OVS_DP_ATTR_USER_FEATURES] = { .type = NLA_U32 },
> +       [OVS_DP_ATTR_MASKS_CACHE_SIZE] =  NLA_POLICY_RANGE(NLA_U32, 0,
> +               PCPU_MIN_UNIT_SIZE / sizeof(struct mask_cache_entry)),
>  };
> Let me know your thoughts

I think its a good idea.  When 'max' becomes too restricted one could
rework internal kernel logic to support larger size and userspace
can detect it by probing with a larger size first.