udevrules: Add rule to set maximum readahead window

Add udev rule to allow tuning the maximum readahead window for the
devices. Also set the default maximum readahead window to 1MB as it
noticeably improves througput for fast NVME drives. For example from 3.6
GB/s with 128k readahead window to 5.0 GB/s with 1MB readahead window.

Signed-off-by: Jan Kara <[email protected]>

Author: jankara

udevrules/60-tune-readahead.rules

@@ -0,0 +1,17 @@
+# --- DO NOT EDIT THIS PART ----
+SUBSYSTEM!="block", GOTO="readahead_end"
+ACTION!="add|change", GOTO="readahead_end"
+ENV{DEVTYPE}!="disk", GOTO="readahead_end"
+TEST!="%S%p/queue/read_ahead_kb", GOTO="readahead_end"
+
+# For dm devices, the relevant events are "change" events, see 10-dm.rules
+ACTION!="change", KERNEL=="dm-*", GOTO="readahead_end"
+
+# --- EDIT BELOW HERE after copying to /etc/udev/rules.d ---
+
+# Set maximum readahead to 1MB
+ATTR{queue/read_ahead_kb}="1024"
+
+# --- EDIT ABOVE HERE after copying to /etc/udev/rules.d ---
+LABEL="readahead_end"
+