Re: [PATCH nft] json: collapse set element commands from parser

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Phil,

On Tue, Nov 05, 2024 at 02:35:16PM +0100, Phil Sutter wrote:
> On Thu, Oct 31, 2024 at 11:04:11PM +0100, Pablo Neira Ayuso wrote:
> > Update json parser to collapse {add,create} element commands to reduce
> > memory consumption in the case of large sets defined by one element per
> > command:
> > 
> > {"nftables": [{"add": {"element": {"family": "ip", "table": "x", "name":
> > "y", "elem": [{"set": ["1.1.0.0"]}]}}},...]}
> 
> Thanks for the fix!
> 
> > Add CTX_F_COLLAPSED flag to report that command has been collapsed.
> 
> I had come up with a similar solution (but did not find time to submit
> it last week). My solution to the "what to return" problem was to
> introduce a 'static struct cmd cmd_nop' and return its address. Your
> flag way is fine, too from my PoV.

OK, I'm going to push it out then.

> > This patch reduces memory consumption by ~32% this case.
> > 
> > Fixes: 20f1c60ac8c8 ("src: collapse set element commands from parser")
> > Reported-by: Eric Garver <eric@garver.life>
> > Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> > ---
> > Side note: While profiling, I can still see lots json objects, this
> > results in memory consumption that is 5 times than native
> > representation. Error reporting is also lagging behind, it should be
> > possible to add a json_t pointer to struct location to relate
> > expressions and json objects.
> 
> I can have a look at mem use if I find spare time (TM).

I understand, that is always the issue.

> We already record links between struct cmd and json_t objects for echo
> mode (and only then). The problem with error reporting in my opinion is
> the lack of location data in json_t. You might remember, I tried to
> extend libjansson to our needs but my MR[1] is being ignored for more
> than a year now. Should we just ship an extended copy in nftables?

Do you still have the link with your proposal around? I don't find it
in my notes anymore.

IIRC the rejection came from concerns about increasing memory usage
for our specific usecase, that was an extra pointer to store location,
correct?

Thanks.