Re: [PATCH v2 10/13] arc: use FLATMEM with freeing of unused memory map instead of DISCONTIGMEM

[Vineet Gupta <vgupta@xxxxxxxxxxxx>]

On 11/16/20 10:57 PM, Mike Rapoport wrote:
> 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>

To avoid any surprises later, I tested that highmem was actually working 
on real hardware (HSDK-4xD dev platform) with modified hsdk.dts to 
enable 2 GB of memory.

       reg = <0x0 0x80000000 0x0 0x40000000    /* 1 GB low mem */
-         0x1 0x00000000 0x0 0x40000000>;  /* 1 GB highmem PAE */
+         0x0 0x00000000 0x0 0x40000000>;  /* 1 GB highmem low phy mem*/
        };

A simple malloc+memset program can allocate upto 1.98 GB of memory.

# cat /proc/meminfo | grep Mem
MemTotal:        2077984 kB
MemFree:         2047512 kB
MemAvailable:    2005712 kB

# /oom 1000 &
# malloc 1000 MB
# Done memset, sleeping for 20 secs

# cat /proc/meminfo | grep Mem
MemTotal:        2077984 kB
MemFree:         1163888 kB
MemAvailable:    1122088 kB

# /oom 980 &
# malloc 980 MB
# Done memset, sleeping for 20 secs

# cat /proc/meminfo | grep Mem
MemTotal:        2077984 kB
MemFree:          239096 kB
MemAvailable:     197296 kB

# Done free.
Done free.

So this is all hunky-dory. Thanks for working on this Mike and improving 
things.

Acked-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>

-Vineet

> > 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