Edit report at https://bugs.php.net/bug.php?id=77879&edit=1
ID: 77879
User updated by: xxalfa at gmail dot com
Reported by: xxalfa at gmail dot com
Summary: Usable memory
Status: Not a bug
Type: Bug
Package: Testing related
Operating System: Windows
PHP Version: 7.3.4
Block user comment: N
Private report: N
New Comment:
Reply to requi...@php.net
I am glad of every answer, only we both do not speak the same language. PHP can
allocate as much memory as it needs. The amount of data I want to process
requires knowing the amount of memory consumed to initiate paging operations.
Any write access to the hard drive takes time, so I want to use as much memory
as possible.
Reply to ni...@php.net
I thank you for your answer, which I now understand the way PHP works. I hope
you can briefly answer my second question? When I open the task manager, I can
keep track of how much memory a script consumes. Although PHP reserves full
RAM, I can only fill it up to 40% at 16 MB. If I set the limit to 41% and fill
the memory, I get a fatal error. In the Task Manager, a value of about 12 MB is
given, why does not "memory_get_usage" provide the true consumption of 12 MB?
Previous Comments:
------------------------------------------------------------------------
[2019-04-12 07:48:07] ni...@php.net
Memory allocations are restricted to certain sizes for performance reasons.
Small allocations are rounded up the next largest bin size. When the memory is
reallocated with a size that still fits within the same bin, the reallocation
is performed in-place and the reported memory usage will not change.
------------------------------------------------------------------------
[2019-04-12 03:06:55] requi...@php.net
No, the memory does not increase by 1024 each time. It increases by whatever
amount PHP allocates in order to expand the string by another 1024 bytes. As
your output shows, the last step it went up by 4096 - enough for approximately
4 increases.
Should it have only allocated 1k? Is it bad that PHP is reserving more memory
than the precise amount it needs at that given moment?
------------------------------------------------------------------------
[2019-04-12 02:58:35] xxalfa at gmail dot com
The script executes successfully because it has detected because the level of
memory has not changed. However, the level increases by 1024 per cycle, if the
function were to work properly, the script would continue to work. That's why
it's a bug.
------------------------------------------------------------------------
[2019-04-12 02:26:32] requi...@php.net
Your script is quitting because PHP didn't need to allocate more memory to
handle another 1k characters. Why is that a bug?
------------------------------------------------------------------------
[2019-04-12 01:48:30] xxalfa at gmail dot com
Description:
------------
The following script fills the memory with pointless data. Now the problem:
From one point, the function "memory_get_usage" returns the same value,
although the level has changed. This is important if you want to process data
and save it only when a certain number of results have been generated. The
second problem: Why are only 40% usable?
Test script:
---------------
<?php
// C:\Users\User\Desktop\php-on-limit.cmd
// @echo off
// title PHP Development Server
// cd "%cd%"
// rem "C:\php\php.exe" "php-on-limit.php"
// "C:\php\php.exe" "-d memory_limit=16M" "php-on-limit.php"
// pause
// C:\Users\User\Desktop\php-on-limit.php [PHP:7.3.3][PID:6336]
//-------------------------------------------------
// HEAD
//-------------------------------------------------
declare( strict_types = 1 );
header( 'Content-Type:text/plain' );
error_reporting( E_ALL );
ini_set( 'display_errors', '1' );
ini_set( 'html_errors', '0' );
define( 'CORE_DIR', dirname( __FILE__ ) . DIRECTORY_SEPARATOR );
isset( $argv ) or trigger_error( 'This is a command terminal application.',
E_USER_ERROR );
echo __FILE__ . ' [PHP:' . phpversion() . '][PID:' . getmypid() . ']' .
PHP_EOL . PHP_EOL;
//-------------------------------------------------
// CODE
//-------------------------------------------------
$measuring_point_of_time = microtime( true );
$memory_limit = conversion_back_to_bytes( ini_get( 'memory_limit' ) );
echo 'memory_limit -- ' . human_readable_file_size( $memory_limit ) . ' --
defined limit' . PHP_EOL;
// $memory_limit *= 0.48; // 48% of 128M can only be used
// $memory_limit *= 0.47; // 47% of 64M can only be used
$memory_limit *= 0.40; // 40% of 16M can only be used
// If the 40% is exceeded, it comes to a fatal error, which is not
desirable.
// Fatal error: Allowed memory size of 16 MByte exhausted (tried to
allocate 6 MByte).
echo 'memory_limit -- ' . human_readable_file_size( $memory_limit ) . ' --
usable limit' . PHP_EOL;
echo 'memory_allocated -- ' . human_readable_file_size( memory_get_usage(
true ) ) . ' -- memory_used -- ' . memory_get_usage() . PHP_EOL;
$something_has_to_be_calculated = true;
$results_of_the_calculations = null;
$last_memory_usage = memory_get_usage();
while ( $something_has_to_be_calculated )
{
$results_of_the_calculations .= str_repeat( '1', 1024 );
$currently_memory_usage = memory_get_usage();
if ( $currently_memory_usage === $last_memory_usage )
{
echo PHP_EOL . 'Process recording: Memory function has not changed.
currently_memory_usage and last_memory_usage are ' . $currently_memory_usage .
PHP_EOL;
break;
}
// echo chr( 0xD );
echo 'memory_allocated -- ' . human_readable_file_size(
memory_get_usage( true ) ) . ' -- memory_used -- ' . memory_get_usage() . ' --
data_length -- ' . strlen( $results_of_the_calculations );
echo PHP_EOL;
if ( memory_get_usage() >= 20 * 1024 * 1024 )
{
echo PHP_EOL . 'Process recording: Normal break.' . PHP_EOL;
break;
}
if ( memory_get_usage() >= $memory_limit )
{
echo PHP_EOL . 'Process recording: Memory limit reached. Save
calculated results so far.' . PHP_EOL;
$results_of_the_calculations = null;
}
$last_memory_usage = memory_get_usage();
}
echo PHP_EOL;
$results_of_the_calculations = null;
echo 'Process recording: Calculations completed. Results are saved.' .
PHP_EOL . PHP_EOL;
echo 'Processing time: ' . elapsed_time( $measuring_point_of_time ) . '
seconds.' . PHP_EOL . PHP_EOL;
//-------------------------------------------------
// FUNCTIONS
//-------------------------------------------------
function elapsed_time( $measuring_point_of_time )
{
return number_format( microtime( true ) - $measuring_point_of_time, 3 );
}
function human_readable_file_size( $file_size, $precision = 2 )
{
$label = array( 'Bytes', 'kByte', 'MByte', 'GByte', 'TByte', 'PByte',
'EByte', 'ZByte', 'YByte' );
return $file_size ? round( $file_size / pow( 1024, ( $index = floor(
log( $file_size, 1024 ) ) ) ), $precision ) . ' ' . $label[ $index ] : '0
Bytes';
}
function conversion_back_to_bytes( $value )
{
$unit = strtolower( substr( $value, -1 ) );
if ( $unit == 'k' ): return (integer) $value * 1024; endif;
if ( $unit == 'm' ): return (integer) $value * 1048576; endif;
if ( $unit == 'g' ): return (integer) $value * 1073741824; endif;
return $value;
}
?>
Expected result:
----------------
The "memory_get_usage" function must continually display the current memory
usage to effectively operate at the memory limit.
Actual result:
--------------
C:\Users\User\Desktop\php-on-limit.php [PHP:7.3.4][PID:1224]
memory_limit -- 16 MByte -- defined limit
memory_limit -- 6.4 MByte -- usable limit
memory_allocated -- 2 MByte -- memory_used -- 410408
memory_allocated -- 2 MByte -- memory_used -- 411688 -- data_length -- 1024
memory_allocated -- 2 MByte -- memory_used -- 412968 -- data_length -- 2048
memory_allocated -- 2 MByte -- memory_used -- 414504 -- data_length -- 3072
memory_allocated -- 2 MByte -- memory_used -- 418600 -- data_length -- 4096
Process recording: Memory function has not changed. currently_memory_usage and
last_memory_usage are 418520
Process recording: Calculations completed. Results are saved.
Processing time: 0.001 seconds.
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=77879&edit=1
