Re: avoiding strdup()

Kaz Kylheku <433-929-6894@kylheku.com> writes:

On 2024-03-11, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

Michael S <already5chosen@yahoo.com> writes:
[...]

Is there any chance at all that on typical Linux machine (i.e. the one
configured to overcommit virtual memory) strdup() returns NULL?
If it was malloc() I'd say - no chance. For strdup() I'm less sure.

>
strdup() calls malloc(), so strdup() can return NULL if and only if
malloc() can return NULL -- but with the additional constraint that you
first need to have a string argument to strdup() that's long enough to
cause a suffiently large argument to be passed to malloc().
>
One data point: On my Ubuntu system, malloc(SIZE_MAX) returns NULL for
very large arguments (over about 23 GiB in my quick and dirty test).

>
I'm guessing that might be only be because of the overcommit_ratio
value; i.e that allowing a 23 GiB increment in the allocated address
space would bring the system over the currently configured overcommit
ratio.

Good guess, but I don't think so.

    $ cat /proc/sys/vm/overcommit_memory
    0
    $ cat /proc/sys/vm/overcommit_ratio
    50

(These are the default values.)  If I'm reading the proc(5) man page
correctly (which is questionable), 0 means "heuristic overcommit", and
overcommit_ratio is ignored unless the mode is set to 2.

I have 12 GB of physical memory.

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Medtronic
void Void(void) { Void(); } /* The recursive call of the void */