netdev - Re: [PATCH nf-next] netfilter: flowtable: separate replace, destroy and stats to different workqueues

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Message-ID: <YFjdb7DveNOolSTr@horizon.localdomain>
Date:   Mon, 22 Mar 2021 15:09:51 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Oz Shlomo <ozsh@...dia.com>, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Paul Blakey <paulb@...dia.com>
Subject: Re: [PATCH nf-next] netfilter: flowtable: separate replace, destroy
 and stats to different workqueues

On Wed, Mar 03, 2021 at 05:11:47PM +0100, Pablo Neira Ayuso wrote:
> Hi,
> 
> On Wed, Mar 03, 2021 at 02:59:53PM +0200, Oz Shlomo wrote:
> > Currently the flow table offload replace, destroy and stats work items are
> > executed on a single workqueue. As such, DESTROY and STATS commands may
> > be backloged after a burst of REPLACE work items. This scenario can bloat
> > up memory and may cause active connections to age.
> > 
> > Instatiate add, del and stats workqueues to avoid backlogs of non-dependent
> > actions. Provide sysfs control over the workqueue attributes, allowing
> > userspace applications to control the workqueue cpumask.
> 
> Probably it would be good to place REPLACE and DESTROY in one single
> queue so workqueues don't race? In case connections are quickly
> created and destroyed, we might get an out of order execution, instead
> of:
> 
>   REPLACE -> DESTROY -> REPLACE
> 
> events could be reordered to:
> 
>   REPLACE -> REPLACE -> DESTROY
> 
> So would it work for you if REPLACE and DESTROY go into one single
> workqueue and stats go into another?
> 
> Or probably make the cookie unique is sufficient? The cookie refers to
> the memory address but memory can be recycled very quickly. If the
> cookie helps to catch the reorder scenario, then the conntrack id
> could be used instead of the memory address as cookie.

Something like this, if I got the idea right, would be even better. If
the entry actually expired before it had a chance of being offloaded,
there is no point in offloading it to then just remove it.

  Marcelo