Re: [iptables PATCH] nft: Eliminate table list from cache

[Phil Sutter <phil@nwl.cc>]

On Fri, Jul 31, 2020 at 01:26:00PM +0200, Pablo Neira Ayuso wrote:
> On Fri, Jul 31, 2020 at 01:25:37PM +0200, Pablo Neira Ayuso wrote:
> > On Fri, Jul 31, 2020 at 01:21:34PM +0200, Phil Sutter wrote:
> > > Hi Pablo,
> > > 
> > > On Thu, Jul 30, 2020 at 09:25:54PM +0200, Pablo Neira Ayuso wrote:
> > > > On Thu, Jul 30, 2020 at 03:57:10PM +0200, Phil Sutter wrote:
> > > > > The full list of tables in kernel is not relevant, only those used by
> > > > > iptables-nft and for those, knowing if they exist or not is sufficient.
> > > > > For holding that information, the already existing 'table' array in
> > > > > nft_cache suits well.
> > > > > 
> > > > > Consequently, nft_table_find() merely checks if the new 'exists' boolean
> > > > > is true or not and nft_for_each_table() iterates over the builtin_table
> > > > > array in nft_handle, additionally checking the boolean in cache for
> > > > > whether to skip the entry or not.
> > > > > 
> > > > > Signed-off-by: Phil Sutter <phil@nwl.cc>
> > > > > ---
> > > > >  iptables/nft-cache.c | 73 +++++++++++---------------------------------
> > > > >  iptables/nft-cache.h |  9 ------
> > > > >  iptables/nft.c       | 55 +++++++++------------------------
> > > > >  iptables/nft.h       |  2 +-
> > > > >  4 files changed, 34 insertions(+), 105 deletions(-)
> > > > 
> > > > This diffstat looks interesting :-)
> > > 
> > > As promised, I wanted to leverage your change for further optimization,
> > > but ended up optimizing your code out along with the old one. :D
> > > 
> > > > One question:
> > > > 
> > > >         c->table[i].exists = true;
> > > > 
> > > > then we assume this table is still in the kernel and we don't recheck?
> > > 
> > > Upon each COMMIT line, nft_action() calls nft_release_cache(). This will
> > > also reset the 'exists' value to false.
> > 
> > Thanks for explaining.
> > 
> > I think the chain cache can also be converted to use linux list,
> > right?
> 
> Having said this, I think it's fine if you push out this.

OK! Looks like I found the problem, it is this 'initialized' boolean
which is not reset when flushing the cache. Looks like more leeway for
streamlining. :)

Cheers, Phil