149 lines
5.1 KiB
Bash
Executable File
149 lines
5.1 KiB
Bash
Executable File
#!/bin/sh
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# Script implements watermark_scale calculation which results in the same low
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# watermark as if extra_free_kbytes tunable were to be used.
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#
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# Usage: extra_free_kbytes.sh <extra_free_kbytes value>
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#
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# extra_free_kbytes is distributed between zones based on
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# zone.managed_pages/vm_total_pages ratio, where vm_total_pages is the sum of
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# zone.managed_pages for all zones (zone.high used in this calculation is 0
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# when this is calculated). Therefore for each zone its share is calculated as:
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#
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# extra_free_pages = extra_free_kbytes / page_size
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# extra_share = extra_free_pages * managed_pages / vm_total_pages
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#
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# This extra_share is added to the low and high watermarks:
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#
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# low = min + max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share
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# high = min + 2 * max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share
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#
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# Because Android uses extra_free_kbytes to adjust the low watermark, we ignore
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# the difference in how watermark_scale and extra_free_kbytes affect the high
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# watermark and will match the low watermark only.
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#
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# To eliminate extra_share and compansate the difference with watermark_scale,
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# a new watermark_scale_new is calculated as:
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#
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# (1) max(min / 4, managed_pages * (watermark_scale / 10000)) + extra_share =
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# max(min / 4, managed_pages * (watermark_scale_new / 10000))
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#
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# Two cases to consider:
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# A. managed_pages * (watermark_scale / 10000) > min / 4
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# The formula (1) becomes:
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#
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# managed_pages * (watermark_scale / 10000) + extra_share =
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# managed_pages * (watermark_scale_new / 10000)
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#
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# after simplifying and substituting extra_share formula becomes:
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#
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# (2) watermark_scale_new = watermark_scale + extra_free_pages / vm_total_pages * 10000
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#
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# B. managed_pages * (watermark_scale / 10000) < min / 4
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# The formula (1) becomes:
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#
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# min / 4 + extra_share = max(min / 4, managed_pages * (watermark_scale_new / 10000))
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#
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# after calculating watermark_scale_new, if (managed_pages * (watermark_scale_new / 10000))
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# is still smaller than min / 4 then we can't compensate extra_share with
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# watermark_scale anyway. Therefore calculation becomes:
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#
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# watermark_scale_new = (min / 4 + extra_share) / managed_pages * 10000
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#
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# after simplifying and substituting extra_share formula becomes:
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#
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# (3) watermark_scale_new = (min / 4) * 10000 / managed_pages + extra_free_pages / vm_total_pages * 10000
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#
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# After defining watermark_delta = extra_free_pages / vm_total_pages * 10000:
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#
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# if (managed_pages * (watermark_scale / 10000) > min / 4)
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# watermark_scale_new = watermark_scale + watermark_delta
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# else
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# watermark_scale_new = (min / 4) * 10000 / managed_pages + watermark_delta
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#
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if [ "$#" -ne 1 ]
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then
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echo "Usage: $0 <extra_free_kbytes value>"
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exit
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fi
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extra_free_kbytes=$1
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# if extra_free_kbytes knob exists, use it and exit
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if [ -e /proc/sys/vm/extra_free_kbytes ]
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then
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echo $extra_free_kbytes > /proc/sys/vm/extra_free_kbytes
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exit
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fi
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# record the original watermark_scale_factor value
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watermark_scale=$(getprop "ro.kernel.watermark_scale_factor")
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if [ -z "$watermark_scale" ]
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then
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watermark_scale=$(cat /proc/sys/vm/watermark_scale_factor)
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setprop "ro.kernel.watermark_scale_factor" "$watermark_scale"
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# On older distributions with no policies configured setprop may fail.
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# If that happens, use the kernel default of 10.
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if [ -z $(getprop "ro.kernel.watermark_scale_factor") ]
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then
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watermark_scale=10
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fi
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fi
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# convert extra_free_kbytes to pages
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page_size=$(getconf PAGESIZE)
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page_size_kb=$((page_size/1024))
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extra_free_pg=$((extra_free_kbytes/page_size_kb))
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managed=($(grep managed /proc/zoneinfo | awk '{print $2}'))
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length=${#managed[@]}
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min=($(grep "min" /proc/zoneinfo | awk '{print $2}'))
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# calculate vm_total_pages.
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# WARNING: if the final low watermark differs from the original, the source of
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# the error is likely vm_total_pages which is impossible to get exact from the
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# userspace. Grep for "Total pages" in the kernel logs to see the actual
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# vm_total_pages and plug it in the calculation to confirm the source of the
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# error. Error caused by this inaccuracy is normally within 1% range.
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vm_total_pages=0
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i=0
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while [ $i -lt $length ]
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do
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vm_total_pages=$((vm_total_pages + managed[i]))
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i=$((i+1))
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done
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# calculate watermark_scale_new for each zone and choose the max
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max_watermark_scale=0
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i=0
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while [ $i -lt $length ]
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do
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# skip unmanaged zones
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if [ ${managed[i]} -eq 0 ]
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then
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i=$((i+1))
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continue
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fi
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base_margin=$((min[i] / 4))
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calc_margin=$(echo "${managed[i]} * $watermark_scale / 10000" | bc)
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# round the value by adding 0.5 and truncating the decimal part
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watermark_delta=$(echo "x=($extra_free_pg / ($vm_total_pages / 10000) + 0.5); scale = 0; x/1" | bc -l)
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if [ $calc_margin -gt $base_margin ]
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then
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watermark_scale_new=$(echo "$watermark_scale + $watermark_delta" | bc)
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else
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watermark_scale_new=$(echo "$base_margin / (${managed[i]} / 10000) + $watermark_delta" | bc)
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fi
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if [ $max_watermark_scale -lt $watermark_scale_new ]
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then
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max_watermark_scale=$watermark_scale_new
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fi
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i=$((i+1))
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done
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echo $max_watermark_scale > /proc/sys/vm/watermark_scale_factor
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