netdev - Re: [PATCH net-next v5] rtnetlink: Support fine-grained netdevice bulk deletion

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Message-ID: <20211208160405.18c7d30f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 8 Dec 2021 16:04:05 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Ahern <dsahern@...il.com>
Cc:     Lahav Schlesinger <lschlesinger@...venets.com>,
        netdev@...r.kernel.org, nikolay@...dia.com
Subject: Re: [PATCH net-next v5] rtnetlink: Support fine-grained netdevice
 bulk deletion

On Wed, 8 Dec 2021 16:43:28 -0700 David Ahern wrote:
> On 12/8/21 2:47 PM, Lahav Schlesinger wrote:
> > No visible changes from what I saw, this API is as fast as group
> > deletion. Maybe a few tens of milliseconds slower, but it's lost in the
> > noise.
> > I'll run more thorough benchmarks to get to a more conclusive conclusion.
> > 
> > Also just pointing out that the sort will be needed even if we pass an
> > array (IFLA_IFINDEX_LIST) instead.
> > Feels like CS 101, but do you have a better approach for detecting
> > duplicates in an array? I imagine a hash table will be slower as it will
> > need to allocate a node object for each device (assuming we don't want
> > to add a new hlist_node to 'struct net_device' just for this)  
> 
> I think marking the dev's and then using a delete loop is going to be
> the better approach - avoid the sort and duplicate problem. I use that
> approach for nexthop deletes:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/net/ipv4/nexthop.c#n1849
> 
> Find a hole in net_device struct in an area used only for control path
> and add 'bool grp_delete' (or a 1-bit hole). Mark the devices on pass
> and delete them on another.

If we want to keep state in the netdev itself we can probably piggy
back on dev->unreg_list. It should be initialized to empty and not
touched unless device goes thru unregister.