How to signal kernel that shared library is not in use by any process anymore ?

[Greg KH]

On Fri, Dec 21, 2018 at 05:20:36PM +0300, Lev Olshvang wrote:
> 
> Hi All,
> 
> I have  an executable (C++) which is the exclusive user of the some shared library that it uses only during  the initialization phase.
> 
> I would like to free memory used by this shared library, because I am running on embedded system.
> 
> How can I achieve this?
> 
> I know that dlopen() will load shared library, and hope that following dlclose() will free this lib memory. 

That right there is how you "achieve" this, call dlclose() and all will
be fine.  If your system needs the memory that was being used, it will
reclaim it from the memory that was previously being used by the library
at this point in time.

Nothing else needs to be done.

Have you tested this and found it not to work properly?

> 1. Still  I do not know what method should be used to make dynamic linker look again into executable and resolve symbols of the newly appeared symbols ?

What "newly appeared symbols"?

If you need to load the library again, call dlopen().

> 2. And  how to tell the dynamic linker ld-linux.so to postpone the symbol resolution until dlopen()  will load  the library?

It will not happen until you tell it to, right?

> 3. Whether to compile and link executable with this library or leave unresolved symbols?

It sounds like you don't really know what type of problem you are trying
to solve here.

Back up, what is the real issue you are having with the kernel at this
point in time?

thanks,

greg k-h