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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Phil Sutter <phil@nwl.cc>, netfilter-devel@vger.kernel.org
Subject: Re: [iptables PATCH v3 04/11] nft-cache: Introduce cache levels
Date: Fri, 11 Oct 2019 12:20:52 +0200
Message-ID: <20191011102052.77s5ujrdb3ficddo@salvia> (raw)
In-Reply-To: <20191010220911.GM12661@orbyte.nwl.cc>

On Fri, Oct 11, 2019 at 12:09:11AM +0200, Phil Sutter wrote:
[...]
> Maybe we could go with a simpler solution for now, which is to check
> kernel genid again and drop the local cache if it differs from what's
> stored. If it doesn't, the current cache is still up to date and we may
> just fetch what's missing. Or does that leave room for a race condition?

My concern with this approach is that, in the dynamic ruleset update
scenarios, assuming very frequent updates, you might lose race when
building the cache in stages. Hence, forcing you to restart from
scratch in the middle of the transaction handling.

I prefer to calculate the cache that is needed in one go by analyzing
the batch, it's simpler. Note that we might lose race still since
kernel might tell us we're working on an obsolete generation number ID
cache, forcing us to restart.

  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-08 16:14 [iptables PATCH v3 00/11] Improve iptables-nft performance with large rulesets Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 01/11] nft: Pass nft_handle to flush_cache() Phil Sutter
2019-10-09  9:30   ` Pablo Neira Ayuso
2019-10-08 16:14 ` [iptables PATCH v3 02/11] nft: Avoid nested cache fetching Phil Sutter
2019-10-09  9:30   ` Pablo Neira Ayuso
2019-10-08 16:14 ` [iptables PATCH v3 03/11] nft: Extract cache routines into nft-cache.c Phil Sutter
2019-10-09  9:32   ` Pablo Neira Ayuso
2019-10-08 16:14 ` [iptables PATCH v3 04/11] nft-cache: Introduce cache levels Phil Sutter
2019-10-09  9:37   ` Pablo Neira Ayuso
2019-10-09 10:29     ` Pablo Neira Ayuso
2019-10-10 22:09       ` Phil Sutter
2019-10-11  9:28         ` Pablo Neira Ayuso
2019-10-11 11:24           ` Phil Sutter
2019-10-14 10:00             ` Pablo Neira Ayuso
2019-10-11 10:20         ` Pablo Neira Ayuso [this message]
2019-10-08 16:14 ` [iptables PATCH v3 05/11] nft-cache: Fetch only chains in nft_chain_list_get() Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 06/11] nft-cache: Cover for multiple fetcher invocation Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 07/11] nft-cache: Support partial cache per table Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 08/11] nft-cache: Support partial rule cache per chain Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 09/11] nft: Reduce cache overhead of nft_chain_builtin_init() Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 10/11] nft: Support nft_is_table_compatible() per chain Phil Sutter
2019-10-08 16:14 ` [iptables PATCH v3 11/11] nft: Optimize flushing all chains of a table Phil Sutter

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