1. MGLRU
Enables Multi-Gen LRU (improved page reclaim and caching policy).
Prevents thrashing, improves loading speeds under low ram conditions.
Requires kernel 6.1+.
Has dramatic effect especially on slower HDDs.
For slower HDDs, consider 1000 instead of 300 for min_ttl_ms.

sudo tee /etc/tmpfiles.d/mglru.conf <<EOF
w-      /sys/kernel/mm/lru_gen/enabled          -       -       -       -       y
w-      /sys/kernel/mm/lru_gen/min_ttl_ms       -       -       -       -       300
EOF


2. ZRAM
Compress memory instead of swapping it to disk.
Greatly improves responsiveness under low ram conditions.
Especially effective on slower HDDs.
For low RAM machines (<=1G) you might want to increase PERCENT to 125 or 150.
There is no contradiction here: the memory is getting compressed only upon
swapping out, reaching 2.5-3 times the compression ratio.

apt install zram-tools
sed -i 's/#PERCENT=.*/PERCENT=75/' /etc/default/zramswap

It is worth setting vm.page-cluster=0 to reduce latency of decompressing

echo vm.page-cluster=0 >> /etc/sysctl.d/85-swappiness.conf

For systems with low RAM and slower HDDs, consider also tuning
swappiness to lower page cache reclamation rate.

echo vm.swappiness=100 >> /etc/sysctl.d/85-swappiness.conf
echo vm.watermark_scale_factor=200 >> /etc/sysctl.d/85-swappiness.conf


3. Eatmydata
Fix Debian/Ubuntu apt/dpkg excessive fsync() calls.
Speeds up software installation.

apt install eatmydata
echo -e '#!/bin/bash\nexec eatmydata /usr/bin/dpkg "$@"' > /usr/local/bin/dpkg
chmod +x /usr/local/bin/dpkg
echo 'Dir::Bin::dpkg "/usr/local/bin/dpkg";' > /etc/apt/apt.conf.d/85eatmydata


4. glibc MALLOC_ARENA_MAX and MALLOC_TRIM_THRESHOLD
Decrease and set static memory allocation arenas to 2.
Decrease and set static heap trimming threshold down to 64KiB.
Reduces overall memory usage.

sed -i 's/#DefaultEnvironment=.*/DefaultEnvironment=MALLOC_ARENA_MAX=2 MALLOC_TRIM_THRESHOLD_=65536/' /etc/systemd/system.conf
echo -e 'export MALLOC_ARENA_MAX=2\nexport MALLOC_TRIM_THRESHOLD_=65536' > /etc/profile.d/85malloc_arena

# Additional files for graphical X11 environment (not for server)
echo -e 'export MALLOC_ARENA_MAX=2\nexport MALLOC_TRIM_THRESHOLD_=65536' > /etc/X11/Xsession.d/85malloc_arena
echo -e 'export MALLOC_ARENA_MAX=2\nexport MALLOC_TRIM_THRESHOLD_=65536' > /etc/X11/xinit/xinitrc.d/85malloc_arena.sh
chmod +x /etc/X11/xinit/xinitrc.d/85malloc_arena.sh