Hello HATAYAMA-san, Sorry for the delayed response, again... On Fri, 29 Mar 2013 17:13:11 +0900 Atsushi Kumagai <kumagai-atsushi at mxc.nes.nec.co.jp> wrote: > Hello HATAYAMA-san, > > Sorry for the delayed response. > > On Tue, 19 Mar 2013 17:47:45 +0900 (JST) > HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote: > > > >> >> What I don't understand well is that the part here: > > >> >> > > >> >> pfn_start = paddr_to_pfn(phys_start); > > >> >> pfn_end = paddr_to_pfn(phys_end); > > >> >> > > >> >> if (!is_in_segs(pfn_to_paddr(pfn_start))) > > >> >> pfn_start++; > > >> >> > > >> >> phys_start and pfn_to_paddr(pfn_start) should belong to the same page > > >> >> frame, so I suspect the pfn_start should be included in vmcore. > > >> >> > > >> >> Looking into kexec-tool side, I don't see additional modification made > > >> >> to phys_start after it's parsed from /proc/iomem or counterpart on EFI > > >> >> interface. Is there any assumption about memory holes behind kernel? > > >> > > > >> > Here is a PT_LOAD segment of ia64 machine which I actually use: > > >> > > > >> > Type Offset VirtAddr PhysAddr > > >> > FileSiz MemSiz Flags Align > > >> > [...] > > >> > LOAD 0x000000015fd0b490 0xe0000040ffda5000 0x00000040ffda5000 > > >> > 0x000000000005a000 0x000000000005a000 RWE 0 > > >> > > > >> > In this case, pfn_to_paddr(pfn_start) is aligned to 0x40ffda4000 > > >> > because the page size is 16KiB, and this address is out of PT_LOAD > > >> > segment. > > >> > > > >> > phys_start > > >> > = 0x40ffda5000 > > >> > |------------- PT_LOAD ---------------- > > >> > ----+----------+----------+----------+-------- > > >> > | pfn:N | pfn:N+1 | pfn:N+2 | ... > > >> > ----+----------+----------+----------+-------- > > >> > | > > >> > pfn_to_paddr(pfn:N) > > >> > = 0x40ffda4000 > > >> > > > >> > The statement you said is for care the case that phys_start isn't aligned > > >> > with the page size. > > >> > > > >> > BTW, I'll add a comment to explain this intention into here. > > >> > > >> Thanks for the pictorial explanation. It's easy to understand. > > >> > > >> Still I think pfn:N should be included in vmcore. The current > > >> implementation drops [0x40ffda5000, 0x40ffda8000] that is contained in > > >> the PT_LOAD. Or, the range must be hole or other kinds of unnecessary > > >> memory from some kernel-side assumption? > > > > > > Oh, I understand your question correctly now. > > > > > > When Ohmichi-san wrote this code, he thought the page which include > > > memory hole isn't be used. This came from the fact that the basic > > > unit of memory management is *page*, but there is no detailed > > > investigation. > > > > You mean on at least IA64 case such parts are always holes? > > I showed the IA64 case just to say that the statement can be executed > actually and it's meaningful code, and this is from my misunderstanding > of your question. > Whether such parts are holes or not is another matter, and I haven't > enough information to decide it now. > > > > > > > So, if there is any case where pfn:N is actually used, this statement > > > should be removed. Maybe, does this question come from an idea of such > > > cases ? > > > > I'm wondering if such case can actually happens. > > I checked a memory map on another IA64 machine and found the regions > that not be aligned by page-size: > > # cat /proc/iomem | grep System > ... > 4040000000-40fea09fff : System RAM > 40fea0a000-40fef5ffff : System RAM // include"pfn:N" 40fea0a000- > 40fef60000-40fef63fff : System RAM > > According to this, it seems that such regions can be exist normally > at least on IA64.?So, what we should investigate is how does kernel > manage such regions (e.g. [0x40fea0a000, 0x40fea0c000]). > And this is the "kernel-side assumption" you said first, right ? First, the memory map(iomem_resource) is made from EFI memory map with efi_initialize_iomem_resources(), then no rounding occurs. And EFI page size is 4KB(EFI_PAGE_SHIFT == 12), so it is natural that some regions aren't aligned by linux kernel page size. Anyway, I found the case that "pfn:N" mentioned in previous mail was actually used on the IA64 machine. > > >> > |------------- PT_LOAD ---------------- > > >> > ----+----------+----------+----------+-------- > > >> > | pfn:N | pfn:N+1 | pfn:N+2 | ... > > >> > ----+----------+----------+----------+-------- Here is the machine's /proc/iomem and dmesg: # cat /proc/iomem | grep System ... 4040000000-40fea09fff : System RAM 40fea0a000-40fef5ffff : System RAM // start address corresponds to "pfn:N" 40fef60000-40fef63fff : System RAM # dmesg ... rsvd_region[0]: [0xe000000001000000, 0xe0000000010000a8) rsvd_region[1]: [0xe000000004000000, 0xe000000004e94e68) rsvd_region[2]: [0xe0000040fea0a010, 0xe0000040fea0a060) // stored in "pfn:N" rsvd_region[3]: [0xe0000040fea0dfd8, 0xe0000040fea0e010) rsvd_region[4]: [0xe0000040fea10000, 0xe0000040fef5fc79) rsvd_region[5]: [0xe0000040fefd0010, 0xe0000040fefd0790) rsvd_region[6]: [0xffffffffffffffff, 0xffffffffffffffff) // these are virtual addresses, __pa(0xe0000040fea0a010) = 0x40fea0a010 According to reserve_memory(), rsvd_region[2] is used to save ia64_boot_param->command_line. This means that "pfn:N" can include valid dates, we shouldn't remove it as holes. Thank you for pointing out this issue, I'll fix it. Atsushi Kumagai
