问题
Why result of php memory_get_peak_usage differs so much from memory size that is shown as allocated to process when using 'top' or 'ps' commands in Linux?
I've set 2 Mb of memory_limit in php.ini My single-string php-script with
echo memory_get_peak_usage(true);
says that it is using 786432 bytes (768 Kb)
If I try to ask system about current php process
echo shell_exec('ps -p '.getmypid().' -Fl');
it gives me
F S UID PID PPID C PRI NI ADDR SZ WCHAN RSS PSR STIME TTY TIME CMD
5 S www-data 14599 14593 0 80 0 - 51322 pipe_w 6976 2 18:53 ? 00:00:00 php-fpm: pool www
RSS param is 6976, so memory usage is 6976 * 4096 = 28573696 = ~28 Mb
Where that 28 Mb come from and is there any way to decrease memory size that is being used by php-fpm process?
回答1:
The memory size is mostly used by the PHP process itself. memory_get_peak_usage() returns the memory used by your specific script. Ways to reduce the memory overhead is to remove the number of extensions, statically compile PHP, etc.. But don't forget that php-fpm (should) fork and that a lot of the memory usage that's not different between PHP process is in fact shared (until it changes).
回答2:
PHP itself may only be set to a 2meg limit, but it's running WITHIN a Apache child process, and that process will have a much higher memory footprint.
If you were running the script from the command line, you'd get memory usage of PHP by itself, as it's not wrapped within Apache and is running on its own.
回答3:
The peak memory usage is for the current script only.
来源：https://stackoverflow.com/questions/7273517/difference-between-memory-get-peak-usage-and-actual-php-process-memory-usage