On Sat, Jan 30, 2021 at 04:37:54PM -0800, Linus Torvalds wrote: > On Sat, Jan 30, 2021 at 2:10 PM Mike Rapoport <rppt@xxxxxxxxxx> wrote: > > > > In either case, e820__memblock_setup() won't add the range 0x0000 - 0x1000 > > to memblock.memory and later during memory map initialization this range is > > left outside any zone. > > Honestly, this just sounds like memblock being stupid in the first place. > > Why aren't these zones padded to sane alignments? The implicit alignment of zones would be a guess. What alignment would be sane here? 1M? MAX_ORDER? pageblock_order? I'm not sure that if an architecture reports its memory at X and we use, say, round_down(X, 1M) for node[0]->node_start_pfn and zone[0]->zone_start_pfn it wouldn't cause boot failure on some system out there in the wild. > This patch smells like working around the memblock code being fragile > rather than a real fix. > > That's *particularly* true when the very line above it did a > "memblock_reserve()" of the exact same range that the memblock_add() > "adds". The most correct thing to do would have been to memblock_add(0, end_of_first_memory_bank); Somewhere at e820__memblock_setup(). But that would mean we also must change the way e820__memblock_setup() reserves memory and that seemed to me like really asking for troubles so I've limited the registration of memory to the range that's for sure reserved. A part of the problem is that x86 adds only usable memory to memblock.memory omitting holes and reserved areas, while free_area_init() presumes that memblock.memory covers populated physical memory. I've tried implicitly adding ranges from memblock.reserved to memblock.memory if they were not there and it had broken some arm machines: https://lore.kernel.org/lkml/127999c4-7d56-0c36-7f88-8e1a5c934cae@xxxxxxxxxxxxx I do feel that free_area_init() is fragile and no doubt there is a room for improvement there. But I think the safer way forward is to reduce inconsistencies between arch and generic code, so that we won't need to guess what is the memory layout at free_area_init() time. > Linus -- Sincerely yours, Mike.
