Hi Mike,
On 11/1/20 9:04 AM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
> Currently ARC uses DISCONTIGMEM to cope with sparse physical memory address
> space on systems with 2 memory banks. While DISCONTIGMEM avoids wasting
> memory on unpopulated memory map, it adds both memory and CPU overhead
> relatively to FLATMEM. Moreover, DISCONTINGMEM is generally considered
> deprecated.
>
> The obvious replacement for DISCONTIGMEM would be SPARSEMEM, but it is also
> less efficient than FLATMEM in pfn_to_page() and page_to_pfn() conversions.
> Besides it requires tuning of SECTION_SIZE which is not trivial for
> possible ARC memory configuration.
>
> Since the memory map for both banks is always allocated from the "lowmem"
> bank, it is possible to use FLATMEM for two-bank configuration and simply
> free the unused hole in the memory map. All is required for that is to
> provide ARC-specific pfn_valid() that will take into account actual
> physical memory configuration and define HAVE_ARCH_PFN_VALID.
>
> The resulting kernel image configured with defconfig + HIGHMEM=y is
> smaller:
>
> $ size a/vmlinux b/vmlinux
> text data bss dec hex filename
> 4673503 1245456 279756 6198715 5e95bb a/vmlinux
> 4658706 1246864 279756 6185326 5e616e b/vmlinux
>
> $ ./scripts/bloat-o-meter a/vmlinux b/vmlinux
> add/remove: 28/30 grow/shrink: 42/399 up/down: 10986/-29025 (-18039)
> ...
> Total: Before=4709315, After=4691276, chg -0.38%
>
> Booting nSIM with haps_ns.dts results in the following memory usage
> reports:
>
> a:
> Memory: 1559104K/1572864K available (3531K kernel code, 595K rwdata, 752K rodata, 136K init, 275K bss, 13760K reserved, 0K cma-reserved, 1048576K highmem)
>
> b:
> Memory: 1559112K/1572864K available (3519K kernel code, 594K rwdata, 752K rodata, 136K init, 280K bss, 13752K reserved, 0K cma-reserved, 1048576K highmem)
>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Sorry this fell through the cracks. Do you have a branch I can checkout
and do a quick test.
Thx,
-Vineet
> ---
> arch/arc/Kconfig | 3 ++-
> arch/arc/include/asm/page.h | 20 +++++++++++++++++---
> arch/arc/mm/init.c | 29 ++++++++++++++++++++++-------
> 3 files changed, 41 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index 0a89cc9def65..c874f8ab0341 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -67,6 +67,7 @@ config GENERIC_CSUM
>
> config ARCH_DISCONTIGMEM_ENABLE
> def_bool n
> + depends on BROKEN
>
> config ARCH_FLATMEM_ENABLE
> def_bool y
> @@ -506,7 +507,7 @@ config LINUX_RAM_BASE
>
> config HIGHMEM
> bool "High Memory Support"
> - select ARCH_DISCONTIGMEM_ENABLE
> + select HAVE_ARCH_PFN_VALID
> help
> With ARC 2G:2G address split, only upper 2G is directly addressable by
> kernel. Enable this to potentially allow access to rest of 2G and PAE
> diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
> index b0dfed0f12be..23e41e890eda 100644
> --- a/arch/arc/include/asm/page.h
> +++ b/arch/arc/include/asm/page.h
> @@ -82,11 +82,25 @@ typedef pte_t * pgtable_t;
> */
> #define virt_to_pfn(kaddr) (__pa(kaddr) >> PAGE_SHIFT)
>
> -#define ARCH_PFN_OFFSET virt_to_pfn(CONFIG_LINUX_RAM_BASE)
> +/*
> + * When HIGHMEM is enabled we have holes in the memory map so we need
> + * pfn_valid() that takes into account the actual extents of the physical
> + * memory
> + */
> +#ifdef CONFIG_HIGHMEM
> +
> +extern unsigned long arch_pfn_offset;
> +#define ARCH_PFN_OFFSET arch_pfn_offset
> +
> +extern int pfn_valid(unsigned long pfn);
> +#define pfn_valid pfn_valid
>
> -#ifdef CONFIG_FLATMEM
> +#else /* CONFIG_HIGHMEM */
> +
> +#define ARCH_PFN_OFFSET virt_to_pfn(CONFIG_LINUX_RAM_BASE)
> #define pfn_valid(pfn) (((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> -#endif
> +
> +#endif /* CONFIG_HIGHMEM */
>
> /*
> * __pa, __va, virt_to_page (ALERT: deprecated, don't use them)
> diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> index 3a35b82a718e..ce07e697916c 100644
> --- a/arch/arc/mm/init.c
> +++ b/arch/arc/mm/init.c
> @@ -28,6 +28,8 @@ static unsigned long low_mem_sz;
> static unsigned long min_high_pfn, max_high_pfn;
> static phys_addr_t high_mem_start;
> static phys_addr_t high_mem_sz;
> +unsigned long arch_pfn_offset;
> +EXPORT_SYMBOL(arch_pfn_offset);
> #endif
>
> #ifdef CONFIG_DISCONTIGMEM
> @@ -98,16 +100,11 @@ void __init setup_arch_memory(void)
> init_mm.brk = (unsigned long)_end;
>
> /* first page of system - kernel .vector starts here */
> - min_low_pfn = ARCH_PFN_OFFSET;
> + min_low_pfn = virt_to_pfn(CONFIG_LINUX_RAM_BASE);
>
> /* Last usable page of low mem */
> max_low_pfn = max_pfn = PFN_DOWN(low_mem_start + low_mem_sz);
>
> -#ifdef CONFIG_FLATMEM
> - /* pfn_valid() uses this */
> - max_mapnr = max_low_pfn - min_low_pfn;
> -#endif
> -
> /*------------- bootmem allocator setup -----------------------*/
>
> /*
> @@ -153,7 +150,9 @@ void __init setup_arch_memory(void)
> * DISCONTIGMEM in turns requires multiple nodes. node 0 above is
> * populated with normal memory zone while node 1 only has highmem
> */
> +#ifdef CONFIG_DISCONTIGMEM
> node_set_online(1);
> +#endif
>
> min_high_pfn = PFN_DOWN(high_mem_start);
> max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
> @@ -161,8 +160,15 @@ void __init setup_arch_memory(void)
> max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
>
> high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
> +
> + arch_pfn_offset = min(min_low_pfn, min_high_pfn);
> kmap_init();
> -#endif
> +
> +#else /* CONFIG_HIGHMEM */
> + /* pfn_valid() uses this when FLATMEM=y and HIGHMEM=n */
> + max_mapnr = max_low_pfn - min_low_pfn;
> +
> +#endif /* CONFIG_HIGHMEM */
>
> free_area_init(max_zone_pfn);
> }
> @@ -190,3 +196,12 @@ void __init mem_init(void)
> highmem_init();
> mem_init_print_info(NULL);
> }
> +
> +#ifdef CONFIG_HIGHMEM
> +int pfn_valid(unsigned long pfn)
> +{
> + return (pfn >= min_high_pfn && pfn <= max_high_pfn) ||
> + (pfn >= min_low_pfn && pfn <= max_low_pfn);
> +}
> +EXPORT_SYMBOL(pfn_valid);
> +#endif
