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Date: Mon, 17 Dec 2018 16:59:19 +0200
From: Nick Kossifidis <mick@....forth.gr>
To: Logan Gunthorpe <logang@...tatee.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-riscv@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org, linux-sh@...r.kernel.org,
Rob Herring <robh@...nel.org>,
Albert Ou <aou@...s.berkeley.edu>,
Andrew Waterman <andrew@...ive.com>,
Arnd Bergmann <arnd@...db.de>,
Palmer Dabbelt <palmer@...ive.com>,
Stephen Bates <sbates@...thlin.com>,
Zong Li <zong@...estech.com>, Olof Johansson <olof@...om.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Michael Clark <michaeljclark@....com>,
Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 6/6] RISC-V: Implement sparsemem
Hello Logan,
Στις 2018-10-15 20:57, Logan Gunthorpe έγραψε:
> This patch implements sparsemem support for risc-v which helps pave the
> way for memory hotplug and eventually P2P support.
>
> We introduce Kconfig options for virtual and physical address bits
> which
> are used to calculate the size of the vmemmap and set the
> MAX_PHYSMEM_BITS.
>
> The vmemmap is located directly before the VMALLOC region and sized
> such that we can allocate enough pages to populate all the virtual
> address space in the system (similar to the way it's done in arm64).
>
> During initialization, call memblocks_present() and sparse_init(),
> and provide a stub for vmemmap_populate() (all of which is similar to
> arm64).
>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Palmer Dabbelt <palmer@...ive.com>
> Cc: Albert Ou <aou@...s.berkeley.edu>
> Cc: Andrew Waterman <andrew@...ive.com>
> Cc: Olof Johansson <olof@...om.net>
> Cc: Michael Clark <michaeljclark@....com>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Zong Li <zong@...estech.com>
> ---
> arch/riscv/Kconfig | 23 +++++++++++++++++++++++
> arch/riscv/include/asm/pgtable.h | 21 +++++++++++++++++----
> arch/riscv/include/asm/sparsemem.h | 11 +++++++++++
> arch/riscv/kernel/setup.c | 4 +++-
> arch/riscv/mm/init.c | 8 ++++++++
> 5 files changed, 62 insertions(+), 5 deletions(-)
> create mode 100644 arch/riscv/include/asm/sparsemem.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index a344980287a5..a1b5d758a542 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -52,12 +52,32 @@ config ZONE_DMA32
> bool
> default y if 64BIT
>
> +config VA_BITS
> + int
> + default 32 if 32BIT
> + default 39 if 64BIT
> +
> +config PA_BITS
> + int
> + default 34 if 32BIT
> + default 56 if 64BIT
> +
> config PAGE_OFFSET
> hex
> default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
> default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
> default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
>
> +config ARCH_FLATMEM_ENABLE
> + def_bool y
> +
> +config ARCH_SPARSEMEM_ENABLE
> + def_bool y
> + select SPARSEMEM_VMEMMAP_ENABLE
> +
> +config ARCH_SELECT_MEMORY_MODEL
> + def_bool ARCH_SPARSEMEM_ENABLE
> +
> config STACKTRACE_SUPPORT
> def_bool y
>
> @@ -92,6 +112,9 @@ config PGTABLE_LEVELS
> config HAVE_KPROBES
> def_bool n
>
> +config HAVE_ARCH_PFN_VALID
> + def_bool y
> +
> menu "Platform type"
>
> choice
> diff --git a/arch/riscv/include/asm/pgtable.h
> b/arch/riscv/include/asm/pgtable.h
> index 16301966d65b..e1162336f5ea 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -89,6 +89,23 @@ extern pgd_t swapper_pg_dir[];
> #define __S110 PAGE_SHARED_EXEC
> #define __S111 PAGE_SHARED_EXEC
>
> +#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> +#define VMALLOC_END (PAGE_OFFSET - 1)
> +#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> +
> +/*
> + * Roughly size the vmemmap space to be large enough to fit enough
> + * struct pages to map half the virtual address space. Then
> + * position vmemmap directly below the VMALLOC region.
> + */
> +#define VMEMMAP_SHIFT \
> + (CONFIG_VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
> +#define VMEMMAP_SIZE (1UL << VMEMMAP_SHIFT)
> +#define VMEMMAP_END (VMALLOC_START - 1)
> +#define VMEMMAP_START (VMALLOC_START - VMEMMAP_SIZE)
> +
> +#define vmemmap ((struct page *)VMEMMAP_START)
> +
> /*
> * ZERO_PAGE is a global shared page that is always zero,
> * used for zero-mapped memory areas, etc.
> @@ -411,10 +428,6 @@ static inline void pgtable_cache_init(void)
> /* No page table caches to initialize */
> }
>
> -#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> -#define VMALLOC_END (PAGE_OFFSET - 1)
> -#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> -
> /*
> * Task size is 0x40000000000 for RV64 or 0xb800000 for RV32.
> * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> diff --git a/arch/riscv/include/asm/sparsemem.h
> b/arch/riscv/include/asm/sparsemem.h
> new file mode 100644
> index 000000000000..215530b24336
> --- /dev/null
> +++ b/arch/riscv/include/asm/sparsemem.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __ASM_SPARSEMEM_H
> +#define __ASM_SPARSEMEM_H
> +
> +#ifdef CONFIG_SPARSEMEM
> +#define MAX_PHYSMEM_BITS CONFIG_PA_BITS
> +#define SECTION_SIZE_BITS 30
Having memory blocks of a minimum size of 1GB doesn't make much sense.
It makes it harder to implement hotplug on top of this since we'll only
able to add/remove 1GB at a time. ARM used to do the same and they
switched to 27bits (https://patchwork.kernel.org/patch/9172845/), ARM64
still uses 1GB, x86 also uses 27bits and most archs also use something
below 30. I believe we should go for 27bits as well or even better have
this as a compile time option.
BTW memblocks_present is on master now (got merged 3 days ago).
Regards,
N.
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