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One way is to donate to devs who are working on some specific features in the Linux kernel. The two I remember are Hector Martin who lead the Asahi Linux project and Kent Overstreet who is the main dev behind bcachefs, a new CoW FS.
But I guess this only works if there is some dev already working on a feature and is accepting donations. I wish we had community linux project or something similar which was funded by donations and hired kernel devs to work on things the community voted on.
Yes, but maybe debian enables it by default? You can check by running
cat /sys/kernel/mm/lru_gen/enabled
If the result is
0x0007
, it means MGLRU is fully enabled.