In lvalue context, 

$var->{$key}

[download]
is equivalent to 
( $var //= {} )->{$key}

[download]
so 
defined( $cg->{mainsnak}{datavalue}{value}{notexist} )

[download]

is equivalent to 

defined( ( ( ( ( $cg //= {} )->{mainsnak} //= {} )->{datavalue} //= {}
+ )->{value} //= {} )->{notexist} )

[download]

That could potentially create a lot of new hashes.

Solution 1: 

if (           $cg
   &&          $cg->{mainsnak}
   &&          $cg->{mainsnak}{datavalue}
   &&          $cg->{mainsnak}{datavalue}{value}
   && defined( $cg->{mainsnak}{datavalue}{value}{notexist} )
) {
   ...
}

[download]

Solution 2: 

no autovivification;
if (defined( $cg->{mainsnak}{datavalue}{value}{notexist} )) {
   ...
}

[download]

In reply to Re: Strange memory growth by ikegami
in thread Strange memory growth by spica1001

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