Re: Question about the "Dynamic reserved memory" patch

양원혁 kjhg4321 at
Fri Mar 13 01:13:49 EDT 2020

> On Fri, 13 Mar 2020 12:06:37 +0900, <kjhg4321 at> said:
> > In the __reserved_mem_reserve_reg() function, I found something that
> > I couldn't easily understand.
> >
> > To get help, I sent an e-mail to this mailing list.
> >
> >                 if (first) {
> >                         fdt_reserved_mem_save_node(node, uname, base, size);
> >                         first = 0;
> >                 }
> >
> > I found that fdt_reserved_mem_save_node() is called the regardless of
> > memblock remove/reserve success.
> >
> > I think early_init_dt_reserve_memory_arch() can fail.(ex. for the lack
> > of memblock's region)
> >
> > So I wonder there will be a situation where reserved_mem
> > initialization will be executed without memory reservation.
> What you probably missed is that function is wrapped in a #ifdef
> CONFIG_OF_EARLY_FLATTREE - and is called to read in the OF devicetree data and
> save it in a form the kernel can use.
> So there usually shouldn't be a problem in reserving memory early in boot,
> unless of course somebody bollixed up a devicetree entry and put in bad values
> for base, size, and nomap.   

But, This is when the early memory allocation is not active. Therefore, if memblock's 
region[128] is full, memblock_reserve/remove() can fail.(Of course, there should be 
more than 128 reserved memory.)

>However, fdt_reserved_mem_save_node() needs to happen anyhow, because that's
>not initialiing the memory that wasn't actually reserved, it's recording the
>fact that the devicetree had a reserved memory request in it, and that needs to
>be remembered because there's a second pass over the devicetree data later on
>(or so the comments in drivers/of/of_reserved_mem.c tell me).

Yes, fdt_reserved_mem_save_node() just register the reseved memory in the reserve_mem.
then, reserved_mem is passed to _reserved_mem_init_node(). But In this function, 
If the node is "cma", it will call rmem_cma_setup() and it will initializing the cma struct,

So what I was wondering was wouldn't the cma structure be initialized without memory 
being reserved?

Kernelnewbies mailing list
Kernelnewbies at

More information about the Kernelnewbies mailing list