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// Usage: php get_max_client.php
// root only.
// 
// This program is used to get MaxClient of apache.
// Following step.
// 1、get all pid of httpd.
// 2、get average Rss of "/proc/$pid/smaps".
// 3、get average Shared_Clean of "/proc/$pid/smaps".
// 4、get average Shared_Dirty of "/proc/$pid/smaps".
// 5、get memory size by free command.
// 6、math max client by "memorySize / (rssAverage - (Shared_Clean + Shared_Dirty))".
// 7、print max client.
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