On 15.12.16 16:07:26, Ard Biesheuvel wrote: > On 15 December 2016 at 15:39, Robert Richter <robert.richter@xxxxxxxxxx> wrote: > > I was going to do some measurements but my kernel crashes now with a > > page fault in efi_rtc_probe(): > > > > [ 21.663393] Unable to handle kernel paging request at virtual address 20251000 > > [ 21.663396] pgd = ffff000009090000 > > [ 21.663401] [20251000] *pgd=0000010ffff90003 > > [ 21.663402] , *pud=0000010ffff90003 > > [ 21.663404] , *pmd=0000000fdc030003 > > [ 21.663405] , *pte=00e8832000250707 > > > > The sparsemem config requires the whole section to be initialized. > > Your patches do not address this. > > > > 96000047 is a third level translation fault, and the PTE address has > RES0 bits set. I don't see how this is related to sparsemem, could you > explain? When initializing the whole section it works. Maybe it uncovers another bug. Did not yet start debugging this. > > > On 14.12.16 09:11:47, Ard Biesheuvel wrote: > >> +config HOLES_IN_ZONE > >> + def_bool y > >> + depends on NUMA > > > > This enables pfn_valid_within() for arm64 and causes the check for > > each page of a section. The arm64 implementation of pfn_valid() is > > already expensive (traversing memblock areas). Now, this is increased > > by a factor of 2^18 for 4k page size (16384 for 64k). We need to > > initialize the whole section to avoid that. > > > > I know that. But if you want something for -stable, we should have > something that is correct first, and only then care about the > performance hit (if there is one) I would prefer to check for a performance penalty *before* we put it into stable. There is nor risk at all with the patch I am proposing. See: https://lkml.org/lkml/2016/12/16/412 -Robert -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>