Re: More than 2, but less than 3 GiB per process memory?
Hello Ron!
You wrote:
> Malte [...] wrote:
> > Does anyone have a clue why 2 GiB is the limit?
>
> http://www.puschitz.com/TuningLinuxForOracle.shtml#AddressMappingsOnLinux
> 0GB-1GB User space - Used for executable and brk/sbrk allocations
> (malloc uses brk for small chunks).
> 1GB-2GB User space - Used for mmaps (shared memory), shared libraries
> and malloc uses mmap (malloc uses mmap for large
> chunks).
> 2GB-3GB User space - Used for stack.
> 3GB-4GB Kernel Space - Used for the kernel itself.
That was very helpful and explains a lot. I wonder whether a comprehensive
documentation like this could be of use in some more official place, hmm.
> > [...]Would using a swap partition
> > instead of a swap file help? The 64G HIGHMEM kernel config option does not
> > seem to make a difference. On a real AMD64 system, the program works fine
> > with >2 GiB RAM, as was expected. Is there any way to make this work,
> > besides changing the algorithm to use less than 2 GiB of memory?
>
> No.
So true. I actually tried changing the PAGE_OFFSET and TASK_UNMAPPED_BASE
divisor in an experimental kernel; this yielded no change for the application
(the value is probably hardcoded in libc6' malloc and g++'s new
implementation? Using the mmap system call directly might have worked, but
having to recompile the base libs to make this work seemed a little extreme)
> > PS: Please Cc: me if possible
>
> If you send question to the list, you should expect the answer
> to only go to the list.
Well, I know that answering to the list is necessary (otherwise other people
might not profit from the solutions found) and I planned to reply to the
list.
Using Debian's web based archive and setting the right References: and
In-Reply-To: headers is somewhat error-prone though (I hope I did not make
any mistakes). A cc: makes it much easier to use the mailer's reply functions
so threading is not broken. Also, the web archive is a pull medium, not a
push medium, so not getting cc:ed is suboptimal.
The other alternative is of course subscribing to the list, which I normally
do, but bandwidth isn't necessarily free everywhere and debian-user is an
extremely high-traffic list. (I'm on dozens of lists, including debian-devel,
but debian-user is just madness unfortunately even with good MUAs). You might
feel profiting from the answers given here while not subscribing is still
unfair, but I actually can't see what enabling the web archive to be used
instead hurts.
I'm not going to reply to the reply-to thread since it's a tangential issue at
best.
Thanks for taking the time,
-Malte
Reply to: