On Tue, Nov 17, 2020 at 06:40:16AM +0000, Vineet Gupta wrote: > 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. It's in mmotm and in my tree: https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git memory-models/rm-discontig/v0 > 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 > -- Sincerely yours, Mike.
