On Tue 13-02-18 14:31:57, Pavel Tatashin wrote: > Memory sections are combined into "memory block" chunks. These chunks are > the units upon which memory can be added and removed. > > On x86, the new memory may be added after the end of the boot memory, > therefore, if block size does not align with end of boot memory, memory > hot-plugging/hot-removing can be broken. > > Currently, whenever machine is boot with more than 64G the block size > unconditionally increased to 2G from the base 128M in order to reduce > number of memory devices in sysfs: > /sys/devices/system/memory/memoryXXX > > But, we must use the largest allowed block size that aligns to the next > address to be able to hotplug the next block of memory. > > So, when memory is larger than 64G, we check the end address and find the > largest block size that is still power of two but smaller or equal to 2G. > > Before, the fix: > Run qemu with: > -m 64G,slots=2,maxmem=66G -object memory-backend-ram,id=mem1,size=2G > > (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 > Block size [0x80000000] unaligned hotplug range: start 0x1040000000, > size 0x80000000 > acpi PNP0C80:00: add_memory failed > acpi PNP0C80:00: acpi_memory_enable_device() error > acpi PNP0C80:00: Enumeration failure > > With the fix memory is added successfully, as the block size is set to 1G, > and therefore aligns with start address 0x1040000000.
I dunno. If x86 maintainers are OK with this then why not, but I do not like how this is x86 specific. I would much rather address this by making the memblock user interface more sane. > Signed-off-by: Pavel Tatashin <[email protected]> > --- > arch/x86/mm/init_64.c | 33 +++++++++++++++++++++++++++++---- > 1 file changed, 29 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 1ab42c852069..f7dc80364397 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -1326,14 +1326,39 @@ int kern_addr_valid(unsigned long addr) > return pfn_valid(pte_pfn(*pte)); > } > > +/* > + * Block size is the minimum quantum of memory which can be hot-plugged or > + * hot-removed. It must be power of two, and must be equal or larger than > + * MIN_MEMORY_BLOCK_SIZE. > + */ > +#define MAX_BLOCK_SIZE (2UL << 30) > + > +/* Amount of ram needed to start using large blocks */ > +#define MEM_SIZE_FOR_LARGE_BLOCK (64UL << 30) > + > static unsigned long probe_memory_block_size(void) > { > - unsigned long bz = MIN_MEMORY_BLOCK_SIZE; > + unsigned long boot_mem_end = max_pfn << PAGE_SHIFT; > + unsigned long bz; > > - /* if system is UV or has 64GB of RAM or more, use large blocks */ > - if (is_uv_system() || ((max_pfn << PAGE_SHIFT) >= (64UL << 30))) > - bz = 2UL << 30; /* 2GB */ > + /* If this is UV system, always set 2G block size */ > + if (is_uv_system()) { > + bz = MAX_BLOCK_SIZE; > + goto done; > + } > > + /* Use regular block if RAM is smaller than MEM_SIZE_FOR_LARGE_BLOCK */ > + if (boot_mem_end < MEM_SIZE_FOR_LARGE_BLOCK) { > + bz = MIN_MEMORY_BLOCK_SIZE; > + goto done; > + } > + > + /* Find the largest allowed block size that aligns to memory end */ > + for (bz = MAX_BLOCK_SIZE; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) { > + if (IS_ALIGNED(boot_mem_end, bz)) > + break; > + } > +done: > pr_info("x86/mm: Memory block size: %ldMB\n", bz >> 20); > > return bz; > -- > 2.16.1 > -- Michal Hocko SUSE Labs
