On Mon, Dec 07, 2020 at 10:49:26AM +0100, Ard Biesheuvel wrote: > On Mon, 7 Dec 2020 at 10:42, Mike Rapoport <r...@linux.ibm.com> wrote: > > > > On Mon, Dec 07, 2020 at 09:35:06AM +0000, Marc Zyngier wrote: > > > On 2020-12-07 09:09, Ard Biesheuvel wrote: > > > > (+ Marc) > > > > > > > > On Fri, 4 Dec 2020 at 12:14, Will Deacon <w...@kernel.org> wrote: > > > > > > > > > > On Fri, Dec 04, 2020 at 09:44:43AM +0800, Wei Li wrote: > > > > > > For the memory hole, sparse memory model that define > > > > > > SPARSEMEM_VMEMMAP > > > > > > do not free the reserved memory for the page map, decrease the > > > > > > section > > > > > > size can reduce the waste of reserved memory. > > > > > > > > > > > > Signed-off-by: Wei Li <liwei...@huawei.com> > > > > > > Signed-off-by: Baopeng Feng <fengbaope...@hisilicon.com> > > > > > > Signed-off-by: Xia Qing <saberlily....@hisilicon.com> > > > > > > --- > > > > > > arch/arm64/include/asm/sparsemem.h | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/arch/arm64/include/asm/sparsemem.h > > > > > > b/arch/arm64/include/asm/sparsemem.h > > > > > > index 1f43fcc79738..8963bd3def28 100644 > > > > > > --- a/arch/arm64/include/asm/sparsemem.h > > > > > > +++ b/arch/arm64/include/asm/sparsemem.h > > > > > > @@ -7,7 +7,7 @@ > > > > > > > > > > > > #ifdef CONFIG_SPARSEMEM > > > > > > #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS > > > > > > -#define SECTION_SIZE_BITS 30 > > > > > > +#define SECTION_SIZE_BITS 27 > > > > > > > > > > We chose '30' to avoid running out of bits in the page flags. What > > > > > changed? > > > > > > > > > > With this patch, I can trigger: > > > > > > > > > > ./include/linux/mmzone.h:1170:2: error: Allocator MAX_ORDER exceeds > > > > > SECTION_SIZE > > > > > #error Allocator MAX_ORDER exceeds SECTION_SIZE > > > > > > > > > > if I bump up NR_CPUS and NODES_SHIFT. > > > > > > > > > > > > > Does this mean we will run into problems with the GICv3 ITS LPI tables > > > > again if we are forced to reduce MAX_ORDER to fit inside > > > > SECTION_SIZE_BITS? > > > > > > Most probably. We are already massively constraint on platforms > > > such as TX1, and dividing the max allocatable range by 8 isn't > > > going to make it work any better... > > > > I don't think MAX_ORDER should shrink. Even if SECTION_SIZE_BITS is > > reduced it should accomodate the existing MAX_ORDER. > > > > My two pennies. > > > > But include/linux/mmzone.h:1170 has this: > > #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS > #error Allocator MAX_ORDER exceeds SECTION_SIZE > #endif > > and Will managed to trigger it after applying this patch.
Right, because with 64K pages section size of 27 bits is not enough to accomodate MAX_ORDER (2^13 pages of 64K). Which means that definition of SECTION_SIZE_BITS should take MAX_ORDER into account either statically with #ifdef ARM64_4K_PAGES #define SECTION_SIZE_BITS <a number> #elif ARM64_16K_PAGES #define SECTION_SIZE_BITS <a larger number> #elif ARM64_64K_PAGES #define SECTION_SIZE_BITS <even larger number> #else #error "and what is the page size?" #endif or dynamically, like e.g. ia64 does: #ifdef CONFIG_FORCE_MAX_ZONEORDER #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) #undef SECTION_SIZE_BITS #define SECTION_SIZE_BITS (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) #endif -- Sincerely yours, Mike.
