netdev - Re: [PATCH 1/4] flow: virtualize flow cache entry methods

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Date:	Sat, 03 Apr 2010 16:50:08 +0300
From:	Timo Teräs <timo.teras@....fi>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] flow: virtualize flow cache entry methods

Herbert Xu wrote:
> With repsect to removing the cache flush upon policy removal,
> what takes care of the timely purging of the corresponding cache
> entries if no new traffic comes through?
> 
> The concern is that if they're not purged in the absence of new
> traffic, then we may hold references on all sorts of objects,
> leading to consequences such as the inability to unregister net
> devices.

The flow cache is randomized every ten minutes. Thus all flow
cache entries get recreated regularly.

> On Sat, Apr 03, 2010 at 11:38:57AM +0800, Herbert Xu wrote:
>> With repsect to removing the cache flush upon policy removal,
>> what takes care of the timely purging of the corresponding cache
>> entries if no new traffic comes through?
> 
> In fact this change would seem to render the existing bundle
> pruning mechanism when devices are unregistered ineffective.
> 
> xfrm_prune_bundles walks through active policy lists to find
> the bundles to purge.  However, if a policy has been deleted
> while a bundle referencing it is still in the cache, that bundle
> will not be pruned.

When policy is killed, the policy->genid is incremented which
makes xfrm_bundle_ok check fail and the bundle to get pruned
immediately on flush.
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