Re: [PATCH v2 08/13] arm: remove CONFIG_ARCH_HAS_HOLES_MEMORYMODEL

From: David Hildenbrand
Date: Mon Nov 02 2020 - 04:44:11 EST

On 01.11.20 18:04, Mike Rapoport wrote:
From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
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@xxxxxxxxxx>

--
Thanks,

David / dhildenb