Description:
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I am using a script retrieving distant content to local system using OAuth fetch function, thus copying the whole files into memory, before writing them to disk using file_put_contents.
That means potentially big files end up in RAM.

My script hangs up in the middle of the loop with a strange and important error:
'NOTICE: PHP message: PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 51366915 bytes)'.
None of my files exceed thos 128MiB, by far.

Using a loop to iterate through files, I started sending to stderr custom error messages to track PHP memory usage and eventually track down any memory leak.

Using (in that specific order) the functions memory_get_usage(), memory_get_usage(true), memory_get_peak_usage() and memory_get_peak_usage(true), I got the following log (sample):
NOTICE: PHP message: 18044352 (18350080) of 31360096 (32505856)

I noticed the values returned by the peak_usage procedures were always the same, equal to 31MiB.

Why is the max possible allocated memory for my script set to 31 MiB?
The 'memory_limit' from PHP Info says 128M, confimed by the fatal error message.