On Thu, Apr 16, 2020 at 03:02:06PM +0900, Masami Hiramatsu wrote:

Hi Luis,

On Wed, 15 Apr 2020 06:30:41 +0000
Luis Chamberlain [off-list ref] wrote:

quoted

Currently the maximum config size size is 32KB and the total key-words
(not     key-value entries) must be under 1024 nodes.  Note: this is not
the number of entries but nodes, an entry must consume more than 2 nodes
(a key-word and a value). So theoretically, it will be up to 512
key-value pairs. If keys contains 3 words in average, it can contain 256
key-value pairs. In most cases, the number of config items will be under
100 entries and smaller than 8KB, so it would be enough.  If the node
number exceeds 1024, parser returns an error even if the file       size
is smaller than 32KB.  Anyway, since bootconfig command verifies it when
appending a boot config       to initrd image, user can notice it before
boot.  

*recommending* bootconfig due to the limitation of cmdline seems
sensible, however if we advise that.. wouldn't the space for 512
theoretical entries full up rather fast?

Yeah, I think it is easier to hit the node number limitation rather
than fill up the space. However, since the bootconfig supports comments,
if user writes enough readable config file, I think it's probably the
right balance :)
If you think the 512 entries is too small, it is easy to expand it
upto 32K (64K nodes). But it may consume 512KB memory only for the
node (meta) data. Current 1024 nodes consumes 8KB (8bytes/node), so
compared with the max data size (32KB), I think it is a better balance.

Yeah, and well at least x86 / x86_64 sets COMMAND_LINE_SIZE to 2048
right now (2 KB), that'd hit the limit of abuse of cmdline pretty fast
too. I see no way to scale this reasonably if people abuse syctls on
the command line but to use bootconfig and bite the bullet on size,
to keep sanity.

  Luis