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Message-ID: <a863af43-be31-4155-95e5-825effcd2aaf@os.amperecomputing.com>
Date: Fri, 23 Jan 2026 10:42:13 -0800
From: Yang Shi <yang@...amperecomputing.com>
To: Anshuman Khandual <anshuman.khandual@....com>, catalin.marinas@....com,
will@...nel.org, ryan.roberts@....com, cl@...two.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [v5 PATCH] arm64: mm: show direct mapping use in /proc/meminfo
Oops, it looks like the similar response was sent twice. My email server
had some hiccups yesterday, I thought the first one was failed to send,
so I sent the other one. But it looks like both went through.
Anyway both are basically same. Sorry for the confusion.
Thanks,
Yang
On 1/22/26 1:41 PM, Yang Shi wrote:
>
>
> On 1/21/26 9:09 PM, Anshuman Khandual wrote:
>> Hello Yang,
>>
>> On 07/01/26 5:59 AM, Yang Shi wrote:
>>> Since commit a166563e7ec3 ("arm64: mm: support large block mapping when
>>> rodata=full"), the direct mapping may be split on some machines instead
>>> keeping static since boot. It makes more sense to show the direct
>>> mapping
>>> use in /proc/meminfo than before.
>> I guess the direct mapping here refers to linear map ? IIUC it is called
>> direct map on x86 and linear map on arm64 platforms. Then should not it
>> be renamed as s/DirectMap/LinearMap instead ? This will align with names
>> from ptdump as well.
>
> Yes, linear map refers to direct map. They are interchangeable in this
> patch. Using "DirectMap" keeps the compatibility with x86.
>
>>
>> Before the above mentioned commit, linear could get altered with memory
>> hotplug and remove events as well.
>>
>>> This patch will make /proc/meminfo show the direct mapping use like the
>>> below (4K base page size):
>>> DirectMap4K: 94792 kB
>>> DirectMap64K: 134208 kB
>>> DirectMap2M: 1173504 kB
>>> DirectMap32M: 5636096 kB
>>> DirectMap1G: 529530880 kB
>> If /proc/meminfo interface is getting updated via arch_report_meminfo()
>> why not add stats for all kernel virtual address space ranges including
>> vmemmap, vmalloc etc aka all address range headers in ptdump as many of
>> those could change during system runtime. What makes linear mapping any
>> special ?
>
> Other than what Will suggested, /proc/meminfo does show vmalloc info:
>
> VmallocTotal: 135288315904 kB
> VmallocUsed: 114200 kB
> VmallocChunk: 0 kB
>
> AFAICT, large block mapping for vmalloc has not been widely used by
> arm64 yet.
> "cat /sys/kernel/debug/kernel_page_tables | grep -e BLK" doesn't show
> any large block mapping on my AmpereOne machine with v6.19-rc4 kernel.
> If we get more large block mappings for vmalloc, we can add the
> mapping size info in the future.
>
> Thanks,
> Yang
>
>>
>>> Although just the machines which support BBML2_NOABORT can split the
>>> direct mapping, show it on all machines regardless of BBML2_NOABORT so
>>> that the users have consistent view in order to avoid confusion.
>>>
>>> Although ptdump also can tell the direct map use, but it needs to dump
>>> the whole kernel page table. It is costly and overkilling. It is also
>>> in debugfs which may not be enabled by all distros. So showing direct
>>> map use in /proc/meminfo seems more convenient and has less overhead.
>> Agreed a /proc/meminfo based broader kernel virtual address space stats
>> display will complement ptdump which provides more granular information
>> about their mapping (with additional cost and setup) but it should cover
>> all the regions in kernel virtual space.
>>
>>> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
>>> ---
>>> v5: * Rebased to v6.19-rc4
>>> * Fixed the build error for !CONFIG_PROC_FS
>>> v4: * Used PAGE_END instead of _PAGE_END(VA_BITS_MIN) per Ryan
>>> * Used shorter name for the helpers and variables per Ryan
>>> * Fixed accounting for memory hotunplug
>>> v3: * Fixed the over-accounting problems per Ryan
>>> * Introduced helpers for add/sub direct map use and #ifdef them
>>> with
>>> CONFIG_PROC_FS per Ryan
>>> * v3 is a fix patch on top of v2
>>> v2: * Counted in size instead of the number of entries per Ryan
>>> * Removed shift array per Ryan
>>> * Use lower case "k" per Ryan
>>> * Fixed a couple of build warnings reported by kernel test robot
>>> * Fixed a couple of poential miscounts
>>>
>>> arch/arm64/mm/mmu.c | 202
>>> +++++++++++++++++++++++++++++++++++++++-----
>>> 1 file changed, 181 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>> index 8e1d80a7033e..422441c9a992 100644
>>> --- a/arch/arm64/mm/mmu.c
>>> +++ b/arch/arm64/mm/mmu.c
>>> @@ -29,6 +29,7 @@
>>> #include <linux/mm_inline.h>
>>> #include <linux/pagewalk.h>
>>> #include <linux/stop_machine.h>
>>> +#include <linux/proc_fs.h>
>>> #include <asm/barrier.h>
>>> #include <asm/cputype.h>
>>> @@ -171,6 +172,85 @@ static void init_clear_pgtable(void *table)
>>> dsb(ishst);
>>> }
>>> +enum dm_type {
>>> + PTE,
>>> + CONT_PTE,
>>> + PMD,
>>> + CONT_PMD,
>>> + PUD,
>>> + NR_DM_TYPE,
>>> +};
>>> +
>>> +#ifdef CONFIG_PROC_FS
>>> +static unsigned long dm_meminfo[NR_DM_TYPE];
>>> +
>>> +void arch_report_meminfo(struct seq_file *m)
>>> +{
>>> + char *size[NR_DM_TYPE];
>>> +
>>> +#if defined(CONFIG_ARM64_4K_PAGES)
>>> + size[PTE] = "4k";
>>> + size[CONT_PTE] = "64k";
>>> + size[PMD] = "2M";
>>> + size[CONT_PMD] = "32M";
>>> + size[PUD] = "1G";
>>> +#elif defined(CONFIG_ARM64_16K_PAGES)
>>> + size[PTE] = "16k";
>>> + size[CONT_PTE] = "2M";
>>> + size[PMD] = "32M";
>>> + size[CONT_PMD] = "1G";
>>> +#elif defined(CONFIG_ARM64_64K_PAGES)
>>> + size[PTE] = "64k";
>>> + size[CONT_PTE] = "2M";
>>> + size[PMD] = "512M";
>>> + size[CONT_PMD] = "16G";
>>> +#endif
>>> +
>>> + seq_printf(m, "DirectMap%s: %8lu kB\n",
>>> + size[PTE], dm_meminfo[PTE] >> 10);
>>> + seq_printf(m, "DirectMap%s: %8lu kB\n",
>>> + size[CONT_PTE],
>>> + dm_meminfo[CONT_PTE] >> 10);
>>> + seq_printf(m, "DirectMap%s: %8lu kB\n",
>>> + size[PMD], dm_meminfo[PMD] >> 10);
>>> + seq_printf(m, "DirectMap%s: %8lu kB\n",
>>> + size[CONT_PMD],
>>> + dm_meminfo[CONT_PMD] >> 10);
>>> + if (pud_sect_supported())
>>> + seq_printf(m, "DirectMap%s: %8lu kB\n",
>>> + size[PUD], dm_meminfo[PUD] >> 10);
>>> +}
>>> +
>>> +static inline bool is_dm_addr(unsigned long addr)
>>> +{
>>> + return (addr >= PAGE_OFFSET) && (addr < PAGE_END);
>>> +}
>>> +
>>> +static inline void dm_meminfo_add(unsigned long addr, unsigned long
>>> size,
>>> + enum dm_type type)
>>> +{
>>> + if (is_dm_addr(addr))
>>> + dm_meminfo[type] += size;
>>> +}
>>> +
>>> +static inline void dm_meminfo_sub(unsigned long addr, unsigned long
>>> size,
>>> + enum dm_type type)
>>> +{
>>> + if (is_dm_addr(addr))
>>> + dm_meminfo[type] -= size;
>>> +}
>>> +#else
>>> +static inline void dm_meminfo_add(unsigned long addr, unsigned long
>>> size,
>>> + enum dm_type type)
>>> +{
>>> +}
>>> +
>>> +static inline void dm_meminfo_sub(unsigned long addr, unsigned long
>>> size,
>>> + enum dm_type type)
>>> +{
>>> +}
>>> +#endif
>>> +
>>> static void init_pte(pte_t *ptep, unsigned long addr, unsigned
>>> long end,
>>> phys_addr_t phys, pgprot_t prot)
>>> {
>>> @@ -236,6 +316,11 @@ static int alloc_init_cont_pte(pmd_t *pmdp,
>>> unsigned long addr,
>>> init_pte(ptep, addr, next, phys, __prot);
>>> + if (pgprot_val(__prot) & PTE_CONT)
>>> + dm_meminfo_add(addr, (next - addr), CONT_PTE);
>>> + else
>>> + dm_meminfo_add(addr, (next - addr), PTE);
>>> +
>>> ptep += pte_index(next) - pte_index(addr);
>>> phys += next - addr;
>>> } while (addr = next, addr != end);
>>> @@ -266,6 +351,17 @@ static int init_pmd(pmd_t *pmdp, unsigned long
>>> addr, unsigned long end,
>>> (flags & NO_BLOCK_MAPPINGS) == 0) {
>>> pmd_set_huge(pmdp, phys, prot);
>>> + /*
>>> + * It is possible to have mappings allow cont mapping
>>> + * but disallow block mapping. For example,
>>> + * map_entry_trampoline().
>>> + * So we have to increase CONT_PMD and PMD size here
>>> + * to avoid double counting.
>>> + */
>>> + if (pgprot_val(prot) & PTE_CONT)
>>> + dm_meminfo_add(addr, (next - addr), CONT_PMD);
>>> + else
>>> + dm_meminfo_add(addr, (next - addr), PMD);
>>> /*
>>> * After the PMD entry has been populated once, we
>>> * only allow updates to the permission attributes.
>>> @@ -389,6 +485,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned
>>> long addr, unsigned long end,
>>> (flags & NO_BLOCK_MAPPINGS) == 0) {
>>> pud_set_huge(pudp, phys, prot);
>>> + dm_meminfo_add(addr, (next - addr), PUD);
>>> /*
>>> * After the PUD entry has been populated once, we
>>> * only allow updates to the permission attributes.
>>> @@ -575,16 +672,21 @@ pgd_pgtable_alloc_special_mm(enum pgtable_type
>>> pgtable_type)
>>> return __pgd_pgtable_alloc(NULL, GFP_PGTABLE_KERNEL,
>>> pgtable_type);
>>> }
>>> -static void split_contpte(pte_t *ptep)
>>> +static void split_contpte(unsigned long addr, pte_t *ptep)
>>> {
>>> int i;
>>> + dm_meminfo_sub(addr, CONT_PTE_SIZE, CONT_PTE);
>>> +
>>> ptep = PTR_ALIGN_DOWN(ptep, sizeof(*ptep) * CONT_PTES);
>>> for (i = 0; i < CONT_PTES; i++, ptep++)
>>> __set_pte(ptep, pte_mknoncont(__ptep_get(ptep)));
>>> +
>>> + dm_meminfo_add(addr, CONT_PTE_SIZE, PTE);
>>> }
>>> -static int split_pmd(pmd_t *pmdp, pmd_t pmd, gfp_t gfp, bool
>>> to_cont)
>>> +static int split_pmd(unsigned long addr, pmd_t *pmdp, pmd_t pmd,
>>> gfp_t gfp,
>>> + bool to_cont)
>>> {
>>> pmdval_t tableprot = PMD_TYPE_TABLE | PMD_TABLE_UXN |
>>> PMD_TABLE_AF;
>>> unsigned long pfn = pmd_pfn(pmd);
>>> @@ -606,8 +708,13 @@ static int split_pmd(pmd_t *pmdp, pmd_t pmd,
>>> gfp_t gfp, bool to_cont)
>>> if (to_cont)
>>> prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>>> + dm_meminfo_sub(addr, PMD_SIZE, PMD);
>>> for (i = 0; i < PTRS_PER_PTE; i++, ptep++, pfn++)
>>> __set_pte(ptep, pfn_pte(pfn, prot));
>>> + if (to_cont)
>>> + dm_meminfo_add(addr, PMD_SIZE, CONT_PTE);
>>> + else
>>> + dm_meminfo_add(addr, PMD_SIZE, PTE);
>>> /*
>>> * Ensure the pte entries are visible to the table walker by
>>> the time
>>> @@ -619,16 +726,21 @@ static int split_pmd(pmd_t *pmdp, pmd_t pmd,
>>> gfp_t gfp, bool to_cont)
>>> return 0;
>>> }
>>> -static void split_contpmd(pmd_t *pmdp)
>>> +static void split_contpmd(unsigned long addr, pmd_t *pmdp)
>>> {
>>> int i;
>>> + dm_meminfo_sub(addr, CONT_PMD_SIZE, CONT_PMD);
>>> +
>>> pmdp = PTR_ALIGN_DOWN(pmdp, sizeof(*pmdp) * CONT_PMDS);
>>> for (i = 0; i < CONT_PMDS; i++, pmdp++)
>>> set_pmd(pmdp, pmd_mknoncont(pmdp_get(pmdp)));
>>> +
>>> + dm_meminfo_add(addr, CONT_PMD_SIZE, PMD);
>>> }
>>> -static int split_pud(pud_t *pudp, pud_t pud, gfp_t gfp, bool
>>> to_cont)
>>> +static int split_pud(unsigned long addr, pud_t *pudp, pud_t pud,
>>> gfp_t gfp,
>>> + bool to_cont)
>>> {
>>> pudval_t tableprot = PUD_TYPE_TABLE | PUD_TABLE_UXN |
>>> PUD_TABLE_AF;
>>> unsigned int step = PMD_SIZE >> PAGE_SHIFT;
>>> @@ -651,8 +763,13 @@ static int split_pud(pud_t *pudp, pud_t pud,
>>> gfp_t gfp, bool to_cont)
>>> if (to_cont)
>>> prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>>> + dm_meminfo_sub(addr, PUD_SIZE, PUD);
>>> for (i = 0; i < PTRS_PER_PMD; i++, pmdp++, pfn += step)
>>> set_pmd(pmdp, pfn_pmd(pfn, prot));
>>> + if (to_cont)
>>> + dm_meminfo_add(addr, PUD_SIZE, CONT_PMD);
>>> + else
>>> + dm_meminfo_add(addr, PUD_SIZE, PMD);
>>> /*
>>> * Ensure the pmd entries are visible to the table walker by
>>> the time
>>> @@ -707,7 +824,7 @@ static int
>>> split_kernel_leaf_mapping_locked(unsigned long addr)
>>> if (!pud_present(pud))
>>> goto out;
>>> if (pud_leaf(pud)) {
>>> - ret = split_pud(pudp, pud, GFP_PGTABLE_KERNEL, true);
>>> + ret = split_pud(addr, pudp, pud, GFP_PGTABLE_KERNEL, true);
>>> if (ret)
>>> goto out;
>>> }
>>> @@ -725,14 +842,14 @@ static int
>>> split_kernel_leaf_mapping_locked(unsigned long addr)
>>> goto out;
>>> if (pmd_leaf(pmd)) {
>>> if (pmd_cont(pmd))
>>> - split_contpmd(pmdp);
>>> + split_contpmd(addr, pmdp);
>>> /*
>>> * PMD: If addr is PMD aligned then addr already describes a
>>> * leaf boundary. Otherwise, split to contpte.
>>> */
>>> if (ALIGN_DOWN(addr, PMD_SIZE) == addr)
>>> goto out;
>>> - ret = split_pmd(pmdp, pmd, GFP_PGTABLE_KERNEL, true);
>>> + ret = split_pmd(addr, pmdp, pmd, GFP_PGTABLE_KERNEL, true);
>>> if (ret)
>>> goto out;
>>> }
>>> @@ -749,7 +866,7 @@ static int
>>> split_kernel_leaf_mapping_locked(unsigned long addr)
>>> if (!pte_present(pte))
>>> goto out;
>>> if (pte_cont(pte))
>>> - split_contpte(ptep);
>>> + split_contpte(addr, ptep);
>>> out:
>>> return ret;
>>> @@ -835,7 +952,7 @@ static int split_to_ptes_pud_entry(pud_t *pudp,
>>> unsigned long addr,
>>> int ret = 0;
>>> if (pud_leaf(pud))
>>> - ret = split_pud(pudp, pud, gfp, false);
>>> + ret = split_pud(addr, pudp, pud, gfp, false);
>>> return ret;
>>> }
>>> @@ -849,8 +966,8 @@ static int split_to_ptes_pmd_entry(pmd_t *pmdp,
>>> unsigned long addr,
>>> if (pmd_leaf(pmd)) {
>>> if (pmd_cont(pmd))
>>> - split_contpmd(pmdp);
>>> - ret = split_pmd(pmdp, pmd, gfp, false);
>>> + split_contpmd(addr, pmdp);
>>> + ret = split_pmd(addr, pmdp, pmd, gfp, false);
>>> /*
>>> * We have split the pmd directly to ptes so there is no
>>> need to
>>> @@ -868,7 +985,7 @@ static int split_to_ptes_pte_entry(pte_t *ptep,
>>> unsigned long addr,
>>> pte_t pte = __ptep_get(ptep);
>>> if (pte_cont(pte))
>>> - split_contpte(ptep);
>>> + split_contpte(addr, ptep);
>>> return 0;
>>> }
>>> @@ -1444,37 +1561,57 @@ static bool pgtable_range_aligned(unsigned
>>> long start, unsigned long end,
>>> return true;
>>> }
>>> -static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,
>>> +static void unmap_hotplug_pte_range(pte_t *ptep, unsigned long addr,
>>> unsigned long end, bool free_mapped,
>>> struct vmem_altmap *altmap)
>>> {
>>> - pte_t *ptep, pte;
>>> + pte_t pte;
>>> do {
>>> - ptep = pte_offset_kernel(pmdp, addr);
>>> pte = __ptep_get(ptep);
>>> if (pte_none(pte))
>>> continue;
>>> WARN_ON(!pte_present(pte));
>>> __pte_clear(&init_mm, addr, ptep);
>>> + dm_meminfo_sub(addr, PAGE_SIZE, PTE);
>>> flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
>>> if (free_mapped)
>>> free_hotplug_page_range(pte_page(pte),
>>> PAGE_SIZE, altmap);
>>> - } while (addr += PAGE_SIZE, addr < end);
>>> + } while (ptep++, addr += PAGE_SIZE, addr < end);
>>> +}
>>> +
>>> +static void unmap_hotplug_cont_pte_range(pmd_t *pmdp, unsigned long
>>> addr,
>>> + unsigned long end, bool free_mapped,
>>> + struct vmem_altmap *altmap)
>>> +{
>>> + unsigned long next;
>>> + pte_t *ptep, pte;
>>> +
>>> + do {
>>> + next = pte_cont_addr_end(addr, end);
>>> + ptep = pte_offset_kernel(pmdp, addr);
>>> + pte = __ptep_get(ptep);
>>> +
>>> + if (pte_present(pte) && pte_cont(pte)) {
>>> + dm_meminfo_sub(addr, CONT_PTE_SIZE, CONT_PTE);
>>> + dm_meminfo_add(addr, CONT_PTE_SIZE, PTE);
>>> + }
>>> +
>>> + unmap_hotplug_pte_range(ptep, addr, next, free_mapped,
>>> altmap);
>>> + } while (addr = next, addr < end);
>>> }
>>> -static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
>>> +static void unmap_hotplug_pmd_range(pmd_t *pmdp, unsigned long addr,
>>> unsigned long end, bool free_mapped,
>>> struct vmem_altmap *altmap)
>>> {
>>> unsigned long next;
>>> - pmd_t *pmdp, pmd;
>>> + pmd_t pmd;
>>> do {
>>> next = pmd_addr_end(addr, end);
>>> - pmdp = pmd_offset(pudp, addr);
>>> pmd = READ_ONCE(*pmdp);
>>> if (pmd_none(pmd))
>>> continue;
>>> @@ -1482,6 +1619,7 @@ static void unmap_hotplug_pmd_range(pud_t
>>> *pudp, unsigned long addr,
>>> WARN_ON(!pmd_present(pmd));
>>> if (pmd_sect(pmd)) {
>>> pmd_clear(pmdp);
>>> + dm_meminfo_sub(addr, PMD_SIZE, PMD);
>>> /*
>>> * One TLBI should be sufficient here as the PMD_SIZE
>>> @@ -1494,7 +1632,28 @@ static void unmap_hotplug_pmd_range(pud_t
>>> *pudp, unsigned long addr,
>>> continue;
>>> }
>>> WARN_ON(!pmd_table(pmd));
>>> - unmap_hotplug_pte_range(pmdp, addr, next, free_mapped,
>>> altmap);
>>> + unmap_hotplug_cont_pte_range(pmdp, addr, next, free_mapped,
>>> altmap);
>>> + } while (pmdp++, addr = next, addr < end);
>>> +}
>>> +
>>> +static void unmap_hotplug_cont_pmd_range(pud_t *pudp, unsigned long
>>> addr,
>>> + unsigned long end, bool free_mapped,
>>> + struct vmem_altmap *altmap)
>>> +{
>>> + unsigned long next;
>>> + pmd_t *pmdp, pmd;
>>> +
>>> + do {
>>> + next = pmd_cont_addr_end(addr, end);
>>> + pmdp = pmd_offset(pudp, addr);
>>> + pmd = READ_ONCE(*pmdp);
>>> +
>>> + if (pmd_leaf(pmd) && pmd_cont(pmd)) {
>>> + dm_meminfo_sub(addr, CONT_PMD_SIZE, CONT_PMD);
>>> + dm_meminfo_add(addr, CONT_PMD_SIZE, PMD);
>>> + }
>>> +
>>> + unmap_hotplug_pmd_range(pmdp, addr, next, free_mapped,
>>> altmap);
>>> } while (addr = next, addr < end);
>>> }
>>> @@ -1515,6 +1674,7 @@ static void unmap_hotplug_pud_range(p4d_t
>>> *p4dp, unsigned long addr,
>>> WARN_ON(!pud_present(pud));
>>> if (pud_sect(pud)) {
>>> pud_clear(pudp);
>>> + dm_meminfo_sub(addr, PUD_SIZE, PUD);
>>> /*
>>> * One TLBI should be sufficient here as the PUD_SIZE
>>> @@ -1527,7 +1687,7 @@ static void unmap_hotplug_pud_range(p4d_t
>>> *p4dp, unsigned long addr,
>>> continue;
>>> }
>>> WARN_ON(!pud_table(pud));
>>> - unmap_hotplug_pmd_range(pudp, addr, next, free_mapped,
>>> altmap);
>>> + unmap_hotplug_cont_pmd_range(pudp, addr, next, free_mapped,
>>> altmap);
>>> } while (addr = next, addr < end);
>>> }
>
>
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