# Solve common flakiness with SSH (MTU discovery on flaky links).
net.ipv4.tcp_mtu_probing=1

# Tune reclaim for swap on zram, which is orders of magnitude faster than the
# disk swapfile these defaults assume.

# Anything above 100 tells the kernel that evicting an anonymous page is
# cheaper than dropping a page-cache page it would have to re-read from disk.
# With a compressed RAM device that is true, so the disk-era default of 60
# leaves the page cache starved. Stop at 150: every page swapped still costs
# a compression now and a decompression on fault-back.
vm.swappiness=150

# Halve the eagerness to drop dentry/inode cache, which is costly to rebuild
# and can't spill to zram. Not lower: 0 can OOM.
vm.vfs_cache_pressure=50

# Read one page per swap-in fault. The default of 8 pays for a seek that zram
# doesn't have, and every extra page costs a separate decompression.
vm.page-cluster=0

# Don't let external fragmentation raise the watermarks, which produces
# reclaim bursts while memory is still free.
vm.watermark_boost_factor=0

# Keep ~1.25% of memory free instead of 0.1%, so kswapd reclaims in the
# background rather than letting allocations stall in direct reclaim.
vm.watermark_scale_factor=125

# Cap dirty pages at 64M/256M instead of the default 10%/20% of RAM, which
# lets gigabytes of writeback pile up and flush in stalling bursts.
vm.dirty_background_bytes=67108864
vm.dirty_bytes=268435456

# With bursts bounded above, the flusher can wake every 15s instead of 5s.
vm.dirty_writeback_centisecs=1500
