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

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Message-ID: <4BB7A2B8.4040405@iki.fi>
Date:	Sat, 03 Apr 2010 23:19:04 +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:
> On Sat, Apr 03, 2010 at 05:26:00PM +0300, Timo Teräs wrote:
>> Why would this block? The device down hook calls flow cache
>> flush. On flush all bundles with non-up devices get pruned
>> immediately (via stale_bundle check).
> 
> Perhaps I missed something in your patch, but the flush that
> we currently perform is limited to the bundles from hashed policies.
> So if a policy has just recently been removed, then its bundles
> won't be flushed.

If a policy is removed, policy->genid is incremented invalidating
the bundles. Those bundles get freed when:
 - specific flow gets hit
 - cache is flushed due to GC call, or interface going down
 - flow cache randomization

If someone is then removing a net driver, we still execute
flush on the 'device down' hook, and all stale bundles
get flushed.

But yes, this means that xfrm_policy struct can now be held
allocated up to ten extra minutes. But it's only memory that
it's holding, not any extra refs. And it's still reclaimable
by the GC.

If this feels troublesome, we could add asynchronous flush
request that would be called on policy removal. Or even stick
to the synchronous one.
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