Linux Sysctl Cleaning To Eventually Erase ~64 Bytes Of Bloat Per Array

Some code cleaning within the sysctl space of the Linux kernel will eventually eliminate around 64 bytes of bloat per array within the kernel where a sentinel can be removed.

An interesting set of patches I hadn't been monitoring have now been picked up by the Linux 6.6 kernel. Luis Chamberlain summed up well the sysctl changes that are ready to go for Linux 6.6 and the impact that it will ultimately have on the kernel:

"Long ago we set out to remove the kitchen sink on kernel/sysctl.c arrays and placings sysctls to their own sybsystem or file to help avoid merge conflicts. Matthew Wilcox pointed out though that if we're going to do that we might as well also *save* space while at it and try to remove the extra last sysctl entry added at the end of each array, a sentintel, instead of bloating the kernel by adding a new sentinel with each array moved.

Doing that was not so trivial, and has required slowing down the moves of kernel/sysctl.c arrays and measuring the impact on size by each new move.

The complex part of the effort to help reduce the size of each sysctl is being done by the patient work of el señor Don Joel Granados. A lot of this is truly painful code refactoring and testing and then trying to measure the savings of each move and removing the sentinels. Although Joel already has code which does most of this work, experience with sysctl moves in the past shows is we need to be careful due to the slew of odd build failures that are possible due to the amount of random Kconfig options sysctls use.

To that end Joel's work is split by first addressing the major housekeeping needed to remove the sentinels, which is part of this merge request. The rest of the work to actually remove the sentinels will be done later in future kernel releases.

At first I was only going to send his first 7 patches of his patch series, posted 1 month ago, but in retrospect due to the testing the changes have received in linux-next and the minor changes they make this goes with the entire set of patches Joel had planned: just sysctl house keeping. There are networking changes but these are part of the house keeping too.

The preliminary math is showing this will all help reduce the overall build time size of the kernel and run time memory consumed by the kernel by about ~64 bytes per array where we are able to remove each sentinel in the future. That also means there is no more bloating the kernel with the extra ~64 bytes per array moved as no new sentinels are created."

This pull request was merged to mainline overnight for the ongoing Linux 6.6 merge window.

Now that's some nice Linux kernel cleaning and hopefully the rest of the work will be wrapped up soon.