On Fri, Apr 25, 2008 at 03:01:23PM +0530, sahlot arvind wrote:No, the loader doesn't need to know anything. It just maps the
> >Now a new process is loaded to memory, which utilizes a .so already in
> memory. How does ld.so know if the required .so is already in >memory and
> what is its physical address?
>
> I think loader keeps track of which libraries are there in the memory and
> their location. Execuatble file of the program contains dependency
> information i.e. which libraries this exe depends upon. So while loading it
> can check whether the required library is always there or not if not then
> loader loads the lib into the memory.
libraries the process needs into its address space. Because linux uses
on-demand paging, nothing will happen at that point. Only when the
process starts to access pages from the library the kernel will load
those pages from disk. If the kernel figures out that particular page
from that particular library was already mapped in another process, it
will just create a map for that page into the current process and
presto: shared mapping of a library.
BTW this is not library specific, it happens with any file that gets
mapped by two (or more) processes. That includes the binaries
themselves, but also mmap()ed files.
Thanks for explanation.
How does the kernel figure out that a particular file/library is already opened and mmaped to a particular address ? Does it scan through the list of open files or is there any information kept in the inode for the file or is there some other way ?
TIA.
Best regards,
Pranav
