if memory_limit is 128M , then any script will use 128MB RAM?

if i set memory_limit开发者_如何学运维 is 128MB. I run a index.php:

<?php
echo 1;
?>

then this script use 128MB RAM ? I think it is not , but want make sure it.

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No it doesn't. 128 MB is just the maximum a script can use, it doesn't necessarily HAVE TO use 128 MB. But it won't be allowed to use anymore than that.

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From the docs (emphasis mine):

This sets the maximum amount of memory in bytes that a script is allowed to allocate.