Re: [1/8,v3] NUMA Hotplug Emulator: add function to hide memory region via e820 table.

Shaohui Zheng
2010-11-19T01:33:25Z

On Thu, Nov 18, 2010 at 01:16:07PM -0800, David Rientjes wrote:
> On Thu, 18 Nov 2010, Shaohui Zheng wrote:
>
> > > > Index: linux-hpe4/arch/x86/kernel/e820.c
> > > > ===================================================================
> > > > --- linux-hpe4.orig/arch/x86/kernel/e820.c 2010-11-15 17:13:02.483461667 +0800
> > > > +++ linux-hpe4/arch/x86/kernel/e820.c 2010-11-15 17:13:07.083461581 +0800
> > > > @@ -971,6 +971,7 @@
> > > > }
> > > >
> > > > static int userdef __initdata;
> > > > +static u64 max_mem_size __initdata = ULLONG_MAX;
> > > >
> > > > /* "mem=nopentium" disables the 4MB page tables. */
> > > > static int __init parse_memopt(char *p)
> > > > @@ -989,12 +990,28 @@
> > > >
> > > > userdef = 1;
> > > > mem_size = memparse(p, &p);
> > > > - e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
> > > > + e820_remove_range(mem_size, max_mem_size - mem_size, E820_RAM, 1);
> > > > + max_mem_size = mem_size;
> > > >
> > > > return 0;
> > > > }
> > >
> > > This needs memmap= support as well, right?
> > we did not do the testing after combine both memmap and numa=hide paramter,
> > I think that the result should similar with mem=XX, they both remove a memory
> > region from the e820 table.
> >
>
> You've modified the parser for mem= but not memmap= so the change needs
> additional support for the latter.
>

the parser for mem= is not modified, the changed parser is numa=, I add a addtional
option numa=hide=.

>From current discussion, numa=hide= interface should be removed, we will use mem=
to hide memory.

> > > > early_param("mem", parse_memopt);
> > > >
> > > > +#ifdef CONFIG_NODE_HOTPLUG_EMU
> > > > +u64 __init e820_hide_mem(u64 mem_size)
> > > > +{
> > > > + u64 start, end_pfn;
> > > > +
> > > > + userdef = 1;
> > > > + end_pfn = e820_end_of_ram_pfn();
> > > > + start = (end_pfn << PAGE_SHIFT) - mem_size;
> > > > + e820_remove_range(start, max_mem_size - start, E820_RAM, 1);
> > > > + max_mem_size = start;
> > > > +
> > > > + return start;
> > > > +}
> > > > +#endif
> > >
> > > This doesn't have any sanity checking for whether e820_remove_range() will
> > > leave any significant amount of memory behind so the kernel will even boot
> > > (probably should have a guaranteed FAKE_NODE_MIN_SIZE left behind?).
> >
> > it should not be checked here, it should be checked by the function who call
> > e820_hide_mem, and truncate the mem_size with FAKE_NODE_MIN_SIZE.
> >
>
> Your patchset doesn't do that, I'm talking specifically about the amount
> of memory left behind so that the kernel at least still boots. That seems
> to be a function of e820_hide_mem() to do some sanity checking so we
> actually still get a kernel rather than the responsibility of the
> command-line parser.

How much memory is enough to make sure the kernel can still boot, it is very
hard to measure. it is almost impossible to get the exact data. I try to leave very
few memory to kernel(hide most memory with numa=hide), it cause a panic directly.

I have no idea about it, do you have any suggestions?

Another example,
I try to add paramter "mem=1M", it compains "Select item can not fit into memory",
and I did not find where the error message comes from, I guess that it should
be printed by grub.