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

[Phil Sutter <phil@nwl.cc>]

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.

> 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).

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?

Cheers, Phil