If we're on a 64-bit machine, the SV headers are always more than 12 bytes, so using 12 as my divisor is safe?

(Do they becomes 16 or 24 bytes on 64-bit systems?)

SVs (and their friends AVs, HVs, etc) are defined in sv.h. They look like: 

struct STRUCT_SV {              /* struct sv { */
    void*       sv_any;         /* pointer to something */
    U32         sv_refcnt;      /* how many references to us */
    U32         sv_flags;       /* what we are */
};

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(AVs, HVs, etc, look the same, except they have a differently typed pointer as the first member of the struct). So their size is 8 bytes (assuming 8 bit bytes), plus the size of a pointer. On a system with 64 bits of addressable memory, pointers will be 8 bytes, giving a struct size of 16 bytes.

As for your other memory related questions, I think you have to dive into malloc.c in the Perl source to get your answer. I looked in the file, and it looks like it's written by someone not familiar with the rest of the perl source code: it actually has large comment sections.

In reply to Re^3: Circular reference testing. by Anonymous Monk
in thread Circular reference testing. by BrowserUk

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