Description:
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When using SimpleXML functions to load XML data, the memory consumption is not tracked internally by PHP. 

Calling the "memory_get_usage()", you can see only a light memory consumption increase, which is clearly not an appropriate value for the document loaded (it is easily seen on a big documents, e.g. 1Mb+). However, the proper memory increase is observed by using system tools ('tasklist /FI "PID eq ..."' under Windows, 'ps' under Linux).

The issue affects profiling scripts, which are not able to fulfill their role. And it affects 'memory_limit' setting, which doesn't control application memory, consumed by SimpleXML.

Test script:
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<?php
echo "Memory usage before: ", memory_get_usage(), "\n";
echo "Sys memory usage before: ", SystemMemoryUsage(), "\n";

$xml = simplexml_load_file('pretty_big_file_of_1mb_size.xml');

echo "Memory usage after: ", memory_get_usage(), "\n";
echo "Sys memory usage after: ", SystemMemoryUsage(), "\n";

/** -------------------------------------- */
function SystemMemoryUsage() 
{
... // Return memory consumption by executing system tool - tasklist, ps or anything else
}



Expected result:
----------------
"Memory usage after" and "Sys memory usage after" show, that memory consumption was increased by approximately same values.

Actual result:
--------------
"Memory usage after" shows light memory consumption increase, while "Sys memory usage after" shows much bigger value.