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Subject: Re: [PATCH v2 08/13] arm: remove CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
To:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Matt Turner <mattst88@gmail.com>, Meelis Roos <mroos@linux.ee>,
        Michael Schmitz <schmitzmic@gmail.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Russell King <linux@armlinux.org.uk>,
        Tony Luck <tony.luck@intel.com>,
        Vineet Gupta <vgupta@synopsys.com>,
        Will Deacon <will@kernel.org>, linux-alpha@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
        linux-mm@kvack.org, linux-snps-arc@lists.infradead.org
References: <20201101170454.9567-1-rppt@kernel.org>
 <20201101170454.9567-9-rppt@kernel.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <81410b81-b773-b4a2-5f03-e9f1a6a8e8e9@redhat.com>
Date:   Mon, 2 Nov 2020 10:43:50 +0100
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On 01.11.20 18:04, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> ARM is the only architecture that defines CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> which in turn enables memmap_valid_within() function that is intended to
> verify existence  of struct page associated with a pfn when there are holes
> in the memory map.
> 
> However, the ARCH_HAS_HOLES_MEMORYMODEL also enables HAVE_ARCH_PFN_VALID
> and arch-specific pfn_valid() implementation that also deals with the holes
> in the memory map.
> 
> The only two users of memmap_valid_within() call this function after
> a call to pfn_valid() so the memmap_valid_within() check becomes redundant.
> 
> Remove CONFIG_ARCH_HAS_HOLES_MEMORYMODEL and memmap_valid_within() and rely
> entirely on ARM's implementation of pfn_valid() that is now enabled
> unconditionally.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>   Documentation/vm/memory-model.rst |  3 +--
>   arch/arm/Kconfig                  |  8 ++------
>   arch/arm/mach-bcm/Kconfig         |  1 -
>   arch/arm/mach-davinci/Kconfig     |  1 -
>   arch/arm/mach-exynos/Kconfig      |  1 -
>   arch/arm/mach-highbank/Kconfig    |  1 -
>   arch/arm/mach-omap2/Kconfig       |  1 -
>   arch/arm/mach-s5pv210/Kconfig     |  1 -
>   arch/arm/mach-tango/Kconfig       |  1 -
>   fs/proc/kcore.c                   |  2 --
>   include/linux/mmzone.h            | 31 -------------------------------
>   mm/mmzone.c                       | 14 --------------
>   mm/vmstat.c                       |  4 ----
>   13 files changed, 3 insertions(+), 66 deletions(-)
> 
> diff --git a/Documentation/vm/memory-model.rst b/Documentation/vm/memory-model.rst
> index 9daadf9faba1..ce398a7dc6cd 100644
> --- a/Documentation/vm/memory-model.rst
> +++ b/Documentation/vm/memory-model.rst
> @@ -51,8 +51,7 @@ call :c:func:`free_area_init` function. Yet, the mappings array is not
>   usable until the call to :c:func:`memblock_free_all` that hands all the
>   memory to the page allocator.
>   
> -If an architecture enables `CONFIG_ARCH_HAS_HOLES_MEMORYMODEL` option,
> -it may free parts of the `mem_map` array that do not cover the
> +An architecture may free parts of the `mem_map` array that do not cover the
>   actual physical pages. In such case, the architecture specific
>   :c:func:`pfn_valid` implementation should take the holes in the
>   `mem_map` into account.
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index fe2f17eb2b50..83adc46c1e67 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -25,7 +25,7 @@ config ARM
>   	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
>   	select ARCH_HAVE_CUSTOM_GPIO_H
>   	select ARCH_HAS_GCOV_PROFILE_ALL
> -	select ARCH_KEEP_MEMBLOCK if HAVE_ARCH_PFN_VALID || KEXEC
> +	select ARCH_KEEP_MEMBLOCK
>   	select ARCH_MIGHT_HAVE_PC_PARPORT
>   	select ARCH_NO_SG_CHAIN if !ARM_HAS_SG_CHAIN
>   	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> @@ -519,7 +519,6 @@ config ARCH_S3C24XX
>   config ARCH_OMAP1
>   	bool "TI OMAP1"
>   	depends on MMU
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARCH_OMAP
>   	select CLKDEV_LOOKUP
>   	select CLKSRC_MMIO
> @@ -1479,9 +1478,6 @@ config OABI_COMPAT
>   	  UNPREDICTABLE (in fact it can be predicted that it won't work
>   	  at all). If in doubt say N.
>   
> -config ARCH_HAS_HOLES_MEMORYMODEL
> -	bool
> -
>   config ARCH_SELECT_MEMORY_MODEL
>   	bool
>   
> @@ -1493,7 +1489,7 @@ config ARCH_SPARSEMEM_ENABLE
>   	select SPARSEMEM_STATIC if SPARSEMEM
>   
>   config HAVE_ARCH_PFN_VALID
> -	def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM
> +	def_bool y
>   
>   config HIGHMEM
>   	bool "High Memory Support"
> diff --git a/arch/arm/mach-bcm/Kconfig b/arch/arm/mach-bcm/Kconfig
> index ae790908fc74..9b594ae98153 100644
> --- a/arch/arm/mach-bcm/Kconfig
> +++ b/arch/arm/mach-bcm/Kconfig
> @@ -211,7 +211,6 @@ config ARCH_BRCMSTB
>   	select BCM7038_L1_IRQ
>   	select BRCMSTB_L2_IRQ
>   	select BCM7120_L2_IRQ
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ZONE_DMA if ARM_LPAE
>   	select SOC_BRCMSTB
>   	select SOC_BUS
> diff --git a/arch/arm/mach-davinci/Kconfig b/arch/arm/mach-davinci/Kconfig
> index f56ff8c24043..de11030748d0 100644
> --- a/arch/arm/mach-davinci/Kconfig
> +++ b/arch/arm/mach-davinci/Kconfig
> @@ -5,7 +5,6 @@ menuconfig ARCH_DAVINCI
>   	depends on ARCH_MULTI_V5
>   	select DAVINCI_TIMER
>   	select ZONE_DMA
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select PM_GENERIC_DOMAINS if PM
>   	select PM_GENERIC_DOMAINS_OF if PM && OF
>   	select REGMAP_MMIO
> diff --git a/arch/arm/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
> index d2d249706ebb..56d272967fc0 100644
> --- a/arch/arm/mach-exynos/Kconfig
> +++ b/arch/arm/mach-exynos/Kconfig
> @@ -8,7 +8,6 @@
>   menuconfig ARCH_EXYNOS
>   	bool "Samsung Exynos"
>   	depends on ARCH_MULTI_V7
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARCH_SUPPORTS_BIG_ENDIAN
>   	select ARM_AMBA
>   	select ARM_GIC
> diff --git a/arch/arm/mach-highbank/Kconfig b/arch/arm/mach-highbank/Kconfig
> index 1bc68913d62c..9de38ce8124f 100644
> --- a/arch/arm/mach-highbank/Kconfig
> +++ b/arch/arm/mach-highbank/Kconfig
> @@ -2,7 +2,6 @@
>   config ARCH_HIGHBANK
>   	bool "Calxeda ECX-1000/2000 (Highbank/Midway)"
>   	depends on ARCH_MULTI_V7
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARCH_SUPPORTS_BIG_ENDIAN
>   	select ARM_AMBA
>   	select ARM_ERRATA_764369 if SMP
> diff --git a/arch/arm/mach-omap2/Kconfig b/arch/arm/mach-omap2/Kconfig
> index 3ee7bdff86b2..89fe1572c142 100644
> --- a/arch/arm/mach-omap2/Kconfig
> +++ b/arch/arm/mach-omap2/Kconfig
> @@ -94,7 +94,6 @@ config SOC_DRA7XX
>   config ARCH_OMAP2PLUS
>   	bool
>   	select ARCH_HAS_BANDGAP
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARCH_HAS_RESET_CONTROLLER
>   	select ARCH_OMAP
>   	select CLKSRC_MMIO
> diff --git a/arch/arm/mach-s5pv210/Kconfig b/arch/arm/mach-s5pv210/Kconfig
> index 95d4e8284866..d644b45bc29d 100644
> --- a/arch/arm/mach-s5pv210/Kconfig
> +++ b/arch/arm/mach-s5pv210/Kconfig
> @@ -8,7 +8,6 @@
>   config ARCH_S5PV210
>   	bool "Samsung S5PV210/S5PC110"
>   	depends on ARCH_MULTI_V7
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARM_VIC
>   	select CLKSRC_SAMSUNG_PWM
>   	select COMMON_CLK_SAMSUNG
> diff --git a/arch/arm/mach-tango/Kconfig b/arch/arm/mach-tango/Kconfig
> index 25b2fd434861..a9eeda36aeb1 100644
> --- a/arch/arm/mach-tango/Kconfig
> +++ b/arch/arm/mach-tango/Kconfig
> @@ -3,7 +3,6 @@ config ARCH_TANGO
>   	bool "Sigma Designs Tango4 (SMP87xx)"
>   	depends on ARCH_MULTI_V7
>   	# Cortex-A9 MPCore r3p0, PL310 r3p2
> -	select ARCH_HAS_HOLES_MEMORYMODEL
>   	select ARM_ERRATA_754322
>   	select ARM_ERRATA_764369 if SMP
>   	select ARM_ERRATA_775420
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index e502414b3556..4d2e64e9016c 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -193,8 +193,6 @@ kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg)
>   		return 1;
>   
>   	p = pfn_to_page(pfn);
> -	if (!memmap_valid_within(pfn, p, page_zone(p)))
> -		return 1;
>   
>   	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
>   	if (!ent)
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 876600a6e891..7385871768d4 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1440,37 +1440,6 @@ void sparse_init(void);
>   #define pfn_valid_within(pfn) (1)
>   #endif
>   
> -#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> -/*
> - * pfn_valid() is meant to be able to tell if a given PFN has valid memmap
> - * associated with it or not. This means that a struct page exists for this
> - * pfn. The caller cannot assume the page is fully initialized in general.
> - * Hotplugable pages might not have been onlined yet. pfn_to_online_page()
> - * will ensure the struct page is fully online and initialized. Special pages
> - * (e.g. ZONE_DEVICE) are never onlined and should be treated accordingly.
> - *
> - * In FLATMEM, it is expected that holes always have valid memmap as long as
> - * there is valid PFNs either side of the hole. In SPARSEMEM, it is assumed
> - * that a valid section has a memmap for the entire section.
> - *
> - * However, an ARM, and maybe other embedded architectures in the future
> - * free memmap backing holes to save memory on the assumption the memmap is
> - * never used. The page_zone linkages are then broken even though pfn_valid()
> - * returns true. A walker of the full memmap must then do this additional
> - * check to ensure the memmap they are looking at is sane by making sure
> - * the zone and PFN linkages are still valid. This is expensive, but walkers
> - * of the full memmap are extremely rare.
> - */
> -bool memmap_valid_within(unsigned long pfn,
> -					struct page *page, struct zone *zone);
> -#else
> -static inline bool memmap_valid_within(unsigned long pfn,
> -					struct page *page, struct zone *zone)
> -{
> -	return true;
> -}
> -#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
> -
>   #endif /* !__GENERATING_BOUNDS.H */
>   #endif /* !__ASSEMBLY__ */
>   #endif /* _LINUX_MMZONE_H */
> diff --git a/mm/mmzone.c b/mm/mmzone.c
> index 4686fdc23bb9..f337831affc2 100644
> --- a/mm/mmzone.c
> +++ b/mm/mmzone.c
> @@ -72,20 +72,6 @@ struct zoneref *__next_zones_zonelist(struct zoneref *z,
>   	return z;
>   }
>   
> -#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> -bool memmap_valid_within(unsigned long pfn,
> -					struct page *page, struct zone *zone)
> -{
> -	if (page_to_pfn(page) != pfn)
> -		return false;
> -
> -	if (page_zone(page) != zone)
> -		return false;
> -
> -	return true;
> -}
> -#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
> -
>   void lruvec_init(struct lruvec *lruvec)
>   {
>   	enum lru_list lru;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 698bc0bc18d1..e292e63afebf 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1503,10 +1503,6 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
>   		if (!page)
>   			continue;
>   
> -		/* Watch for unexpected holes punched in the memmap */
> -		if (!memmap_valid_within(pfn, page, zone))
> -			continue;
> -

Right, pfn_to_online_page() -> pfn_valid() / pfn_valid_within() should 
handle that.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb