[PATCH 11/13] arch, mm: streamline HIGHMEM freeing

From: Mike Rapoport
Date: Thu Mar 06 2025 - 13:55:10 EST

From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>

All architectures that support HIGHMEM have their code that frees high
memory pages to the buddy allocator while __free_memory_core() is limited
to freeing only low memory.

There is no actual reason for that. The memory map is completely ready
by the time memblock_free_all() is called and high pages can be released to
the buddy allocator along with low memory.

Remove low memory limit from __free_memory_core() and drop per-architecture
code that frees high memory pages.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
arch/arc/mm/init.c | 6 +-----
arch/arm/mm/init.c | 29 -----------------------------
arch/csky/mm/init.c | 14 --------------
arch/microblaze/mm/init.c | 16 ----------------
arch/mips/mm/init.c | 20 --------------------
arch/powerpc/mm/mem.c | 14 --------------
arch/sparc/mm/init_32.c | 25 -------------------------
arch/x86/include/asm/highmem.h | 3 ---
arch/x86/include/asm/numa.h | 4 ----
arch/x86/include/asm/numa_32.h | 13 -------------
arch/x86/mm/Makefile | 2 --
arch/x86/mm/highmem_32.c | 34 ----------------------------------
arch/x86/mm/init_32.c | 28 ----------------------------
arch/xtensa/mm/init.c | 29 -----------------------------
include/linux/mm.h | 1 -
mm/memblock.c | 3 +--
16 files changed, 2 insertions(+), 239 deletions(-)
delete mode 100644 arch/x86/include/asm/numa_32.h
delete mode 100644 arch/x86/mm/highmem_32.c

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index 05025122e965..11ce638731c9 100644
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -160,11 +160,7 @@ void __init setup_arch_memory(void)
static void __init highmem_init(void)
{
#ifdef CONFIG_HIGHMEM
- unsigned long tmp;
-
memblock_phys_free(high_mem_start, high_mem_sz);
- for (tmp = min_high_pfn; tmp < max_high_pfn; tmp++)
- free_highmem_page(pfn_to_page(tmp));
#endif
}

@@ -176,8 +172,8 @@ static void __init highmem_init(void)
*/
void __init mem_init(void)
{
- memblock_free_all();
highmem_init();
+ memblock_free_all();

BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index d4bcc745a044..7bb5ce02b9b5 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -237,33 +237,6 @@ static inline void poison_init_mem(void *s, size_t count)
*p++ = 0xe7fddef0;
}

-static void __init free_highpages(void)
-{
-#ifdef CONFIG_HIGHMEM
- unsigned long max_low = max_low_pfn;
- phys_addr_t range_start, range_end;
- u64 i;
-
- /* set highmem page free */
- for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE,
- &range_start, &range_end, NULL) {
- unsigned long start = PFN_UP(range_start);
- unsigned long end = PFN_DOWN(range_end);
-
- /* Ignore complete lowmem entries */
- if (end <= max_low)
- continue;
-
- /* Truncate partial highmem entries */
- if (start < max_low)
- start = max_low;
-
- for (; start < end; start++)
- free_highmem_page(pfn_to_page(start));
- }
-#endif
-}
-
/*
* mem_init() marks the free areas in the mem_map and tells us how much
* memory is free. This is done after various parts of the system have
@@ -283,8 +256,6 @@ void __init mem_init(void)
/* this will put all unused low memory onto the freelists */
memblock_free_all();

- free_highpages();
-
/*
* Check boundaries twice: Some fundamental inconsistencies can
* be detected at build time already.
diff --git a/arch/csky/mm/init.c b/arch/csky/mm/init.c
index a22801aa503a..3914c2b873da 100644
--- a/arch/csky/mm/init.c
+++ b/arch/csky/mm/init.c
@@ -44,21 +44,7 @@ EXPORT_SYMBOL(empty_zero_page);

void __init mem_init(void)
{
-#ifdef CONFIG_HIGHMEM
- unsigned long tmp;
-#endif
-
memblock_free_all();
-
-#ifdef CONFIG_HIGHMEM
- for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) {
- struct page *page = pfn_to_page(tmp);
-
- /* FIXME not sure about */
- if (!memblock_is_reserved(tmp << PAGE_SHIFT))
- free_highmem_page(page);
- }
-#endif
}

void free_initmem(void)
diff --git a/arch/microblaze/mm/init.c b/arch/microblaze/mm/init.c
index 7e2e342e84c5..3e664e0efc33 100644
--- a/arch/microblaze/mm/init.c
+++ b/arch/microblaze/mm/init.c
@@ -52,19 +52,6 @@ static void __init highmem_init(void)
map_page(PKMAP_BASE, 0, 0); /* XXX gross */
pkmap_page_table = virt_to_kpte(PKMAP_BASE);
}
-
-static void __meminit highmem_setup(void)
-{
- unsigned long pfn;
-
- for (pfn = max_low_pfn; pfn < max_pfn; ++pfn) {
- struct page *page = pfn_to_page(pfn);
-
- /* FIXME not sure about */
- if (!memblock_is_reserved(pfn << PAGE_SHIFT))
- free_highmem_page(page);
- }
-}
#endif /* CONFIG_HIGHMEM */

/*
@@ -122,9 +109,6 @@ void __init mem_init(void)
{
/* this will put all memory onto the freelists */
memblock_free_all();
-#ifdef CONFIG_HIGHMEM
- highmem_setup();
-#endif

mem_init_done = 1;
}
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 99cefb58fba3..e7882874ba2f 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -427,25 +427,6 @@ void __init paging_init(void)
static struct kcore_list kcore_kseg0;
#endif

-static inline void __init mem_init_free_highmem(void)
-{
-#ifdef CONFIG_HIGHMEM
- unsigned long tmp;
-
- if (cpu_has_dc_aliases)
- return;
-
- for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) {
- struct page *page = pfn_to_page(tmp);
-
- if (!memblock_is_memory(PFN_PHYS(tmp)))
- SetPageReserved(page);
- else
- free_highmem_page(page);
- }
-#endif
-}
-
void __init mem_init(void)
{
/*
@@ -456,7 +437,6 @@ void __init mem_init(void)

maar_init();
setup_zero_pages(); /* Setup zeroed pages. */
- mem_init_free_highmem();
memblock_free_all();

#ifdef CONFIG_64BIT
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index c7708c8fad29..1bc94bca9944 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -297,20 +297,6 @@ void __init mem_init(void)

memblock_free_all();

-#ifdef CONFIG_HIGHMEM
- {
- unsigned long pfn, highmem_mapnr;
-
- highmem_mapnr = lowmem_end_addr >> PAGE_SHIFT;
- for (pfn = highmem_mapnr; pfn < max_mapnr; ++pfn) {
- phys_addr_t paddr = (phys_addr_t)pfn << PAGE_SHIFT;
- struct page *page = pfn_to_page(pfn);
- if (memblock_is_memory(paddr) && !memblock_is_reserved(paddr))
- free_highmem_page(page);
- }
- }
-#endif /* CONFIG_HIGHMEM */
-
#if defined(CONFIG_PPC_E500) && !defined(CONFIG_SMP)
/*
* If smp is enabled, next_tlbcam_idx is initialized in the cpu up
diff --git a/arch/sparc/mm/init_32.c b/arch/sparc/mm/init_32.c
index 81a468a9c223..043e9b6fadd0 100644
--- a/arch/sparc/mm/init_32.c
+++ b/arch/sparc/mm/init_32.c
@@ -232,18 +232,6 @@ static void __init taint_real_pages(void)
}
}

-static void map_high_region(unsigned long start_pfn, unsigned long end_pfn)
-{
- unsigned long tmp;
-
-#ifdef CONFIG_DEBUG_HIGHMEM
- printk("mapping high region %08lx - %08lx\n", start_pfn, end_pfn);
-#endif
-
- for (tmp = start_pfn; tmp < end_pfn; tmp++)
- free_highmem_page(pfn_to_page(tmp));
-}
-
void __init mem_init(void)
{
int i;
@@ -276,19 +264,6 @@ void __init mem_init(void)
taint_real_pages();

memblock_free_all();
-
- for (i = 0; sp_banks[i].num_bytes != 0; i++) {
- unsigned long start_pfn = sp_banks[i].base_addr >> PAGE_SHIFT;
- unsigned long end_pfn = (sp_banks[i].base_addr + sp_banks[i].num_bytes) >> PAGE_SHIFT;
-
- if (end_pfn <= highstart_pfn)
- continue;
-
- if (start_pfn < highstart_pfn)
- start_pfn = highstart_pfn;
-
- map_high_region(start_pfn, end_pfn);
- }
}

void sparc_flush_page_to_ram(struct page *page)
diff --git a/arch/x86/include/asm/highmem.h b/arch/x86/include/asm/highmem.h
index 731ee7cc40a5..585bdadba47d 100644
--- a/arch/x86/include/asm/highmem.h
+++ b/arch/x86/include/asm/highmem.h
@@ -69,9 +69,6 @@ extern unsigned long highstart_pfn, highend_pfn;
arch_flush_lazy_mmu_mode(); \
} while (0)

-extern void add_highpages_with_active_regions(int nid, unsigned long start_pfn,
- unsigned long end_pfn);
-
#endif /* __KERNEL__ */

#endif /* _ASM_X86_HIGHMEM_H */
diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h
index 5469d7a7c40f..53ba39ce010c 100644
--- a/arch/x86/include/asm/numa.h
+++ b/arch/x86/include/asm/numa.h
@@ -41,10 +41,6 @@ static inline int numa_cpu_node(int cpu)
}
#endif /* CONFIG_NUMA */

-#ifdef CONFIG_X86_32
-# include <asm/numa_32.h>
-#endif
-
#ifdef CONFIG_NUMA
extern void numa_set_node(int cpu, int node);
extern void numa_clear_node(int cpu);
diff --git a/arch/x86/include/asm/numa_32.h b/arch/x86/include/asm/numa_32.h
deleted file mode 100644
index 9c8e9e85be77..000000000000
--- a/arch/x86/include/asm/numa_32.h
+++ /dev/null
@@ -1,13 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_X86_NUMA_32_H
-#define _ASM_X86_NUMA_32_H
-
-#ifdef CONFIG_HIGHMEM
-extern void set_highmem_pages_init(void);
-#else
-static inline void set_highmem_pages_init(void)
-{
-}
-#endif
-
-#endif /* _ASM_X86_NUMA_32_H */
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 690fbf48e853..52fbf0a60858 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -42,8 +42,6 @@ obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
obj-$(CONFIG_PTDUMP_CORE) += dump_pagetables.o
obj-$(CONFIG_PTDUMP_DEBUGFS) += debug_pagetables.o

-obj-$(CONFIG_HIGHMEM) += highmem_32.o
-
KASAN_SANITIZE_kasan_init_$(BITS).o := n
obj-$(CONFIG_KASAN) += kasan_init_$(BITS).o

diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
deleted file mode 100644
index d9efa35711ee..000000000000
--- a/arch/x86/mm/highmem_32.c
+++ /dev/null
@@ -1,34 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-#include <linux/highmem.h>
-#include <linux/export.h>
-#include <linux/swap.h> /* for totalram_pages */
-#include <linux/memblock.h>
-#include <asm/numa.h>
-
-void __init set_highmem_pages_init(void)
-{
- struct zone *zone;
- int nid;
-
- /*
- * Explicitly reset zone->managed_pages because set_highmem_pages_init()
- * is invoked before memblock_free_all()
- */
- reset_all_zones_managed_pages();
- for_each_zone(zone) {
- unsigned long zone_start_pfn, zone_end_pfn;
-
- if (!is_highmem(zone))
- continue;
-
- zone_start_pfn = zone->zone_start_pfn;
- zone_end_pfn = zone_start_pfn + zone->spanned_pages;
-
- nid = zone_to_nid(zone);
- printk(KERN_INFO "Initializing %s for node %d (%08lx:%08lx)\n",
- zone->name, nid, zone_start_pfn, zone_end_pfn);
-
- add_highpages_with_active_regions(nid, zone_start_pfn,
- zone_end_pfn);
- }
-}
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 801b659ead0c..9ee8ec2bc5d1 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -394,23 +394,6 @@ static void __init permanent_kmaps_init(pgd_t *pgd_base)

pkmap_page_table = virt_to_kpte(vaddr);
}
-
-void __init add_highpages_with_active_regions(int nid,
- unsigned long start_pfn, unsigned long end_pfn)
-{
- phys_addr_t start, end;
- u64 i;
-
- for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &start, &end, NULL) {
- unsigned long pfn = clamp_t(unsigned long, PFN_UP(start),
- start_pfn, end_pfn);
- unsigned long e_pfn = clamp_t(unsigned long, PFN_DOWN(end),
- start_pfn, end_pfn);
- for ( ; pfn < e_pfn; pfn++)
- if (pfn_valid(pfn))
- free_highmem_page(pfn_to_page(pfn));
- }
-}
#else
static inline void permanent_kmaps_init(pgd_t *pgd_base)
{
@@ -715,17 +698,6 @@ void __init mem_init(void)
#ifdef CONFIG_FLATMEM
BUG_ON(!mem_map);
#endif
- /*
- * With CONFIG_DEBUG_PAGEALLOC initialization of highmem pages has to
- * be done before memblock_free_all(). Memblock use free low memory for
- * temporary data (see find_range_array()) and for this purpose can use
- * pages that was already passed to the buddy allocator, hence marked as
- * not accessible in the page tables when compiled with
- * CONFIG_DEBUG_PAGEALLOC. Otherwise order of initialization is not
- * important here.
- */
- set_highmem_pages_init();
-
/* this will put all low memory onto the freelists */
memblock_free_all();

diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index 9b662477b3d4..47ecbe28263e 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -129,41 +129,12 @@ void __init zones_init(void)
print_vm_layout();
}

-static void __init free_highpages(void)
-{
-#ifdef CONFIG_HIGHMEM
- unsigned long max_low = max_low_pfn;
- phys_addr_t range_start, range_end;
- u64 i;
-
- /* set highmem page free */
- for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE,
- &range_start, &range_end, NULL) {
- unsigned long start = PFN_UP(range_start);
- unsigned long end = PFN_DOWN(range_end);
-
- /* Ignore complete lowmem entries */
- if (end <= max_low)
- continue;
-
- /* Truncate partial highmem entries */
- if (start < max_low)
- start = max_low;
-
- for (; start < end; start++)
- free_highmem_page(pfn_to_page(start));
- }
-#endif
-}
-
/*
* Initialize memory pages.
*/

void __init mem_init(void)
{
- free_highpages();
-
memblock_free_all();
}

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fdf20503850e..6fccd3b3248c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3172,7 +3172,6 @@ extern void reserve_bootmem_region(phys_addr_t start,

/* Free the reserved page into the buddy system, so it gets managed. */
void free_reserved_page(struct page *page);
-#define free_highmem_page(page) free_reserved_page(page)

static inline void mark_page_reserved(struct page *page)
{
diff --git a/mm/memblock.c b/mm/memblock.c
index 95af35fd1389..64ae678cd1d1 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2164,8 +2164,7 @@ static unsigned long __init __free_memory_core(phys_addr_t start,
phys_addr_t end)
{
unsigned long start_pfn = PFN_UP(start);
- unsigned long end_pfn = min_t(unsigned long,
- PFN_DOWN(end), max_low_pfn);
+ unsigned long end_pfn = PFN_DOWN(end);

if (start_pfn >= end_pfn)
return 0;
--
2.47.2