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Date:	Fri, 19 Mar 2010 08:32:29 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Timo Teräs <timo.teras@....fi>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] xfrm: cache bundle lookup results in flow cache

On Thu, Mar 18, 2010 at 09:30:58PM +0200, Timo Teräs wrote:
>
>>> I don't see why we can't maintain the policy use time if we did
>>> this, all you need is a back-pointer from the top xfrm_dst.
>>
>> Sure.
>
> Actually no. As the pmtu case showed, it's more likely that
> xfrm_dst needs to be regenerated, but the policy stays the
> same since policy db isn't touched that often. If we keep
> them separately we can almost most of the time avoid doing
> policy lookup which is also O(n). Also the currently cache
> entry validation is needs to check policy's bundles_genid
> before allowing touching of xfrm_dst. Otherwise we would have
> to keep global bundle_genid, and we'd lose the parent pointer
> on cache miss.

A back-pointer does not require an O(n) lookup.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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