On Wed, Apr 15, 2020 at 12:23:59PM +0900, Masami Hiramatsu wrote: > Hi Vlastimil, > > On Tue, 14 Apr 2020 13:32:19 +0200 > Vlastimil Babka <vbabka@xxxxxxx> wrote: > > > This series adds support for something that seems like many people always > > wanted but nobody added it yet, so here's the ability to set sysctl parameters > > via kernel command line options in the form of sysctl.vm.something=1 > > Sounds good. And would you consider to use the bootconfig instead of (or > in addition to) the kernel command line, because it is too short to describe > the sysctl options? FWIW for the lazy: The cmdline limitation: Documentation/admin-guide/kernel-parameters.rst ``` The number of kernel parameters is not limited, but the length of the complete command line (parameters including spaces etc.) is limited to a fixed number of characters. This limit depends on the architecture and is between 256 and 4096 characters. It is defined in the file ./include/asm/setup.h as COMMAND_LINE_SIZE. ``` The bootconfig limitation: Documentation/admin-guide/bootconfig.rst ``` 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? Luis
