Merge changes from topic "extra_free_kbytes.sh"
* changes:
Use extra_free_kbytes.sh whenever sys.sysctl.extra_free_kbytes changes
init: Add extra_free_kbytes.sh script to adjust watermark_scale_factor
diff --git a/init/Android.bp b/init/Android.bp
index a04d2db..5d09687 100644
--- a/init/Android.bp
+++ b/init/Android.bp
@@ -236,6 +236,7 @@
"init.rc",
"ueventd.rc",
"e2fsdroid",
+ "extra_free_kbytes.sh",
"make_f2fs",
"mke2fs",
"sload_f2fs",
@@ -552,3 +553,8 @@
},
},
}
+
+sh_binary {
+ name: "extra_free_kbytes.sh",
+ src: "extra_free_kbytes.sh",
+}
diff --git a/init/extra_free_kbytes.sh b/init/extra_free_kbytes.sh
new file mode 100755
index 0000000..aeaa912
--- /dev/null
+++ b/init/extra_free_kbytes.sh
@@ -0,0 +1,136 @@
+#!/bin/sh
+
+# Script implements watermark_scale calculation which results in the same low
+# watermark as if extra_free_kbytes tunable were to be used.
+#
+# Usage: extra_free_kbytes.sh <extra_free_kbytes value>
+#
+# extra_free_kbytes is distributed between zones based on
+# zone.managed_pages/vm_total_pages ratio, where vm_total_pages is the sum of
+# zone.managed_pages for all zones (zone.high used in this calculation is 0
+# when this is calculated). Therefore for each zone its share is calculated as:
+#
+# extra_free_pages = extra_free_kbytes / page_size
+# extra_share = extra_free_pages * managed_pages / vm_total_pages
+#
+# This extra_share is added to the low and high watermarks:
+#
+# low = min + max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share
+# high = min + 2 * max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share
+#
+# Because Android uses extra_free_kbytes to adjust the low watermark, we ignore
+# the difference in how watermark_scale and extra_free_kbytes affect the high
+# watermark and will match the low watermark only.
+#
+# To eliminate extra_share and compansate the difference with watermark_scale,
+# a new watermark_scale_new is calculated as:
+#
+# (1) max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share =
+# max(min / 4, managed_pages * (watermark_scale_new / 10000))
+#
+# Two cases to consider:
+# A. managed_pages * (watermark_scale / 10000) > min / 4
+# The formula (1) becomes:
+#
+# managed_pages * (watermark_scale / 10000) + extra_share =
+# managed_pages * (watermark_scale_new / 10000)
+#
+# after simplifying and substituting extra_share formula becomes:
+#
+# (2) watermark_scale_new = watermark_scale + extra_free_pages / vm_total_pages * 10000
+#
+# B. managed_pages * (watermark_scale / 10000) < min / 4
+# The formula (1) becomes:
+#
+# min / 4 + extra_share = max(min / 4, managed_pages * (watermark_scale_new / 10000))
+#
+# after calculating watermark_scale_new, if (managed_pages * (watermark_scale_new / 10000))
+# is still smaller than min / 4 then we can't compensate extra_share with
+# watermark_scale anyway. Therefore calculation becomes:
+#
+# watermark_scale_new = (min / 4 + extra_share) / managed_pages * 10000
+#
+# after simplifying and substituting extra_share formula becomes:
+#
+# (3) watermark_scale_new = (min / 4) * 10000 / managed_pages + extra_free_pages / vm_total_pages * 10000
+#
+# After defining watermark_delta = extra_free_pages / vm_total_pages * 10000:
+#
+# if (managed_pages * (watermark_scale / 10000) > min / 4)
+# watermark_scale_new = watermark_scale + watermark_delta
+# else
+# watermark_scale_new = (min / 4) * 10000 / managed_pages + watermark_delta
+#
+
+if [ "$#" -ne 1 ]
+then
+ echo "Usage: $0 <extra_free_kbytes value>"
+ exit
+fi
+
+extra_free_kbytes=$1
+
+# if extra_free_kbytes knob exists, use it and exit
+if [ -e /proc/sys/vm/extra_free_kbytes ]
+then
+ echo $extra_free_kbytes > /proc/sys/vm/extra_free_kbytes
+ exit
+fi
+
+watermark_scale=`cat /proc/sys/vm/watermark_scale_factor`
+
+# convert extra_free_kbytes to pages
+page_size=$(getconf PAGESIZE)
+page_size_kb=$((page_size/1024))
+extra_free_pg=$((extra_free_kbytes/page_size_kb))
+
+managed=($(grep managed /proc/zoneinfo | awk '{print $2}'))
+length=${#managed[@]}
+min=($(grep "min" /proc/zoneinfo | awk '{print $2}'))
+
+# calculate vm_total_pages.
+# WARNING: if the final low watermark differs from the original, the source of
+# the error is likely vm_total_pages which is impossible to get exact from the
+# userspace. Grep for "Total pages" in the kernel logs to see the actual
+# vm_total_pages and plug it in the calculation to confirm the source of the
+# error. Error caused by this inaccuracy is normally within 1% range.
+vm_total_pages=0
+i=0
+while [ $i -lt $length ]
+do
+ vm_total_pages=$((vm_total_pages + managed[i]))
+ i=$((i+1))
+done
+
+# calculate watermark_scale_new for each zone and choose the max
+max_watermark_scale=0
+i=0
+while [ $i -lt $length ]
+do
+ # skip unmanaged zones
+ if [ ${managed[i]} -eq 0 ]
+ then
+ i=$((i+1))
+ continue
+ fi
+
+ base_margin=$((min[i] / 4))
+ calc_margin=$(echo "${managed[i]} * $watermark_scale / 10000" | bc)
+ # round the value by adding 0.5 and truncating the decimal part
+ watermark_delta=$(echo "x=($extra_free_pg / ($vm_total_pages / 10000) + 0.5); scale = 0; x/1" | bc -l)
+ if [ $calc_margin -gt $base_margin ]
+ then
+ watermark_scale_new=$(echo "$watermark_scale + $watermark_delta" | bc)
+ else
+ watermark_scale_new=$(echo "$base_margin / (${managed[i]} / 10000) + $watermark_delta" | bc)
+ fi
+
+ if [ $max_watermark_scale -lt $watermark_scale_new ]
+ then
+ max_watermark_scale=$watermark_scale_new
+ fi
+
+ i=$((i+1))
+done
+
+echo $max_watermark_scale > /proc/sys/vm/watermark_scale_factor
diff --git a/rootdir/init.rc b/rootdir/init.rc
index ab0aff5..9371617 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -1138,7 +1138,7 @@
# and chown/chmod does not work for /proc/sys/ entries.
# So proxy writes through init.
on property:sys.sysctl.extra_free_kbytes=*
- write /proc/sys/vm/extra_free_kbytes ${sys.sysctl.extra_free_kbytes}
+ exec -- /system/bin/extra_free_kbytes.sh ${sys.sysctl.extra_free_kbytes}
# Allow users to drop caches
on property:perf.drop_caches=3