How to return GC-d memory back to OS

Oskar Linde oskar.lindeREM at
Thu Aug 3 09:05:01 PDT 2006

Serg Kovrov wrote:
> Is it possible to make GC to free memory back to OS?
> I'm asking because I'm writing a news feed notifier/reader, and my goal 
> for the application is to be as much memory efficient as possible, as I 
> intent to run it on my desktop 24/7.
> In other words, I want my application to free any resources back to OS 
> as soon as they no longer used. eg., it fetch a big document, process it 
> store for later usage on disk cache, set a flag that new document 
> available - then free all resources used for that task back to OS. 
> Whatever peak memory usage will be, I want my application in idle state 
> to have as small memory footprint as possible.
> The 'high watermark' (if thats the name) approach in GC is not way to go 
> in my case =(
> There is not much info on GC on digitalmars site, so maybe someone know 
> a workaround for my situation?

For a long time, even linux malloc()/free() would not return memory to 
the OS. Usually, memory is allocated from the OS using brk() or similar 
system calls and an application can only return memory from the end of 
the virtual address range the application has been allocated. In 
general, this requires a relocating/compacting GC, as even a single 
allocated byte at the top end of your virtual address space will prevent 
the OS from shrinking it.

But apart from needing much swap space, there are no draw backs of using 
much virtual memory. The memory you don't use (but exists in your 
virtual address range) will not map to physical memory and will not 
affect your computers performance.


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