Re: [PATCH] mm/hotplug: Only respect mem= parameter during boot stage

[JÃrgen GroÃ]

On 09.12.19 12:01, David Hildenbrand wrote:
> On 09.12.19 11:24, JÃrgen Groà wrote:
> > On 09.12.19 11:07, Michal Hocko wrote:
> > > On Fri 06-12-19 23:05:24, Baoquan He wrote:
> > > > In commit 357b4da50a62 ("x86: respect memory size limiting via mem=
> > > > parameter") a global varialbe global max_mem_size is added to store
> > > > the value which is parsed from 'mem= '. This truly stops those
> > > > DIMM from being added into system memory during boot.
> > > >
> > > > However, it also limits the later memory hotplug functionality. Any
> > > > memory board can't be hot added any more if its region is beyond the
> > > > max_mem_size. System will print error like below:
> > > >
> > > > [  216.387164] acpi PNP0C80:02: add_memory failed
> > > > [  216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
> > > > [  216.392187] acpi PNP0C80:02: Enumeration failure
> > > >
> > > > >From document of 'mem =' parameter, it should be a restriction during
> > > > boot, but not impact the system memory adding/removing after booting.
> > > >
> > > >     mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
> > > >
> > > > So fix it by also checking if it's during SYSTEM_BOOTING stage when
> > > > restrict memory adding. Otherwise, skip the restriction.
> > >
> > > Could you be more specific about why the boot vs. later hotplug makes
> > > any difference? The documentation is explicit about the boot time but
> > > considering this seems to be like that since ever I strongly suspect
> > > that this is just an omission.
> > >
> > > Btw. how have you tested the situation fixed by 357b4da50a62?
> >
> > I guess he hasn't.
> >
> > The backtrace of the problem at that time was:
> >
> > [ 8321.876844]  [<ffffffff81019ab9>] dump_trace+0x59/0x340
> > [ 8321.882683]  [<ffffffff81019e8a>] show_stack_log_lvl+0xea/0x170
> > [ 8321.889298]  [<ffffffff8101ac31>] show_stack+0x21/0x40
> > [ 8321.895043]  [<ffffffff81319530>] dump_stack+0x5c/0x7c
> > [ 8321.900779]  [<ffffffff8107fbf1>] warn_slowpath_common+0x81/0xb0
> > [ 8321.907482]  [<ffffffff81009f54>] xen_alloc_pte+0x1d4/0x390
> > [ 8321.913718]  [<ffffffff81064950>]
> > pmd_populate_kernel.constprop.6+0x40/0x80
> > [ 8321.921498]  [<ffffffff815ef0a8>] phys_pmd_init+0x210/0x255
> > [ 8321.927724]  [<ffffffff815ef2c7>] phys_pud_init+0x1da/0x247
> > [ 8321.933951]  [<ffffffff815efb81>] kernel_physical_mapping_init+0xf5/0x1d4
> > [ 8321.941533]  [<ffffffff815ebc7d>] init_memory_mapping+0x18d/0x380
> > [ 8321.948341]  [<ffffffff810647f9>] arch_add_memory+0x59/0xf0
> > [ 8321.954570]  [<ffffffff815eceed>] add_memory_resource+0x8d/0x160
> > [ 8321.961283]  [<ffffffff815ecff2>] add_memory+0x32/0xf0
> > [ 8321.967025]  [<ffffffff813e1c91>] acpi_memory_device_add+0x131/0x2e0
> > [ 8321.974128]  [<ffffffff8139f752>] acpi_bus_attach+0xe2/0x190
> > [ 8321.980453]  [<ffffffff8139f6ce>] acpi_bus_attach+0x5e/0x190
> > [ 8321.986778]  [<ffffffff8139f6ce>] acpi_bus_attach+0x5e/0x190
> > [ 8321.993103]  [<ffffffff8139f6ce>] acpi_bus_attach+0x5e/0x190
> > [ 8321.999428]  [<ffffffff813a1157>] acpi_bus_scan+0x37/0x70
> > [ 8322.005461]  [<ffffffff81fba955>] acpi_scan_init+0x77/0x1b4
> > [ 8322.011690]  [<ffffffff81fba70c>] acpi_init+0x297/0x2b3
> > [ 8322.017530]  [<ffffffff8100213a>] do_one_initcall+0xca/0x1f0
> > [ 8322.023855]  [<ffffffff81f74266>] kernel_init_freeable+0x194/0x226
> > [ 8322.030760]  [<ffffffff815eb1ba>] kernel_init+0xa/0xe0
> > [ 8322.036503]  [<ffffffff815f7bc5>] ret_from_fork+0x55/0x80
> >
> > So this patch would break it again.
> >
> > I'd recommend ...
> >
> > > > Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem= parameter")
> > > > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > > > ---
> > > >    mm/memory_hotplug.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > > > index 55ac23ef11c1..5466a0a00901 100644
> > > > --- a/mm/memory_hotplug.c
> > > > +++ b/mm/memory_hotplug.c
> > > > @@ -105,7 +105,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
> > > >    	unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > > >    	char *resource_name = "System RAM";
> > > >    
> > > > -	if (start + size > max_mem_size)
> > > > +	if (start + size > max_mem_size && system_state == SYSTEM_BOOTING)
> >
> > ... changing this to: ... && system_state != SYSTEM_RUNNING
>
> I think we usually use system_state < SYSTEM_RUNNING

Works for me as well. :-)


Juergen