vm_stat 和 Activity Monitor.app 的 OSX 内存读数不一致

Question

我正在尝试编写一个脚本来监视内存状态。这是我到目前为止所拥有的：

# Memory Usage
ramactive=$(vm_stat | grep "Pages active" | while read a b c; do echo "$((${c%?}*4096/1024/1024))"; done)
ramwired=$(vm_stat | grep "Pages wired" | while read a b c d; do echo "$((${d%?}*4096/1024/1024))"; done)
ramspec=$(vm_stat | grep "Pages speculative" | while read a b c; do echo "$((${c%?}*4096/1024/1024))"; done)
raminactive=$(vm_stat | grep "Pages inactive" | while read a b c; do echo "$((${c%?}*4096/1024/1024))"; done)
ramfree=$(vm_stat | grep "Pages free" | while read a b c; do echo "$((${c%?}*4096/1024/1024))"; done)
rampurge=$(vm_stat | grep "Pages purgeable" | while read a b c; do echo "$((${c%?}*4096/1024/1024))"; done)

printf "RAM\n"
printf "%-11s%'.f MB Used\n" "Active:" "$ramactive"
printf "%-11s%'.f MB Used\n" "Wired:" "$ramwired"

printf "%-11s%'.f MB Used\n" "Inactive:" "$raminactive"
printf "%-11s%'.f MB Used\n" "Spec:" "$ramspec"
printf "%-11s%'.f MB Used\n" "Cached:" "$(($ramspec+$raminactive))"

printf "%-11s%'.f MB Used\n" "Free:" "$ramfree"

printf "%-11s%'.f MB Used\n" "Total Used:" "$(($ramwired+$ramactive))"
printf "%-11s%'.f MB Used\n" "Used-Purge:" "$(($ramwired+$ramactive-$rampurge))"
printf "%-11s%'.f MB Used\n" "Total Free:" "$(($ramfree+$ramspec+$raminactive))"
printf "%-11s%'.f MB Used\n" "Total RAM:" "$(($ramactive+$ramwired+$ramspec+$raminactive+$ramfree))"

我只是在这里进行实验，所以这不是最终的脚本。但我无法从这里获取与活动监视器相匹配的数字。例如，我的计算机上的活动 + 有线内存显示为 9 GB，而活动监视器声称只有 6.5 GB。有线内存读数匹配，但活动读数不匹配。我在这里缺少什么？