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Date: Wed, 9 Sep 2020 10:36:16 -0400
From: Zi Yan <ziy@...dia.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>
CC: <linux-mm@...ck.org>, Roman Gushchin <guro@...com>,
Rik van Riel <riel@...riel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Matthew Wilcox <willy@...radead.org>,
Shakeel Butt <shakeelb@...gle.com>,
Yang Shi <yang.shi@...ux.alibaba.com>,
David Nellans <dnellans@...dia.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 05/16] mm: thp: handling 1GB THP reference bit.
On 9 Sep 2020, at 10:09, Kirill A. Shutemov wrote:
> On Wed, Sep 02, 2020 at 02:06:17PM -0400, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> Add PUD-level TLB flush ops and teach page_vma_mapped_talk about 1GB
>> THPs.
>>
>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>> arch/x86/include/asm/pgtable.h | 3 +++
>> arch/x86/mm/pgtable.c | 13 +++++++++++++
>> include/linux/mmu_notifier.h | 13 +++++++++++++
>> include/linux/pgtable.h | 14 ++++++++++++++
>> include/linux/rmap.h | 1 +
>> mm/page_vma_mapped.c | 33 +++++++++++++++++++++++++++++----
>> mm/rmap.c | 12 +++++++++---
>> 7 files changed, 82 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>> index 26255cac78c0..15334f5ba172 100644
>> --- a/arch/x86/include/asm/pgtable.h
>> +++ b/arch/x86/include/asm/pgtable.h
>> @@ -1127,6 +1127,9 @@ extern int pudp_test_and_clear_young(struct vm_area_struct *vma,
>> extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
>> unsigned long address, pmd_t *pmdp);
>>
>> +#define __HAVE_ARCH_PUDP_CLEAR_YOUNG_FLUSH
>> +extern int pudp_clear_flush_young(struct vm_area_struct *vma,
>> + unsigned long address, pud_t *pudp);
>>
>> #define pmd_write pmd_write
>> static inline int pmd_write(pmd_t pmd)
>> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
>> index 7be73aee6183..e4a2dffcc418 100644
>> --- a/arch/x86/mm/pgtable.c
>> +++ b/arch/x86/mm/pgtable.c
>> @@ -633,6 +633,19 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
>>
>> return young;
>> }
>> +int pudp_clear_flush_young(struct vm_area_struct *vma,
>> + unsigned long address, pud_t *pudp)
>> +{
>> + int young;
>> +
>> + VM_BUG_ON(address & ~HPAGE_PUD_MASK);
>> +
>> + young = pudp_test_and_clear_young(vma, address, pudp);
>> + if (young)
>> + flush_tlb_range(vma, address, address + HPAGE_PUD_SIZE);
>> +
>> + return young;
>> +}
>> #endif
>>
>> /**
>> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
>> index b8200782dede..4ffa179e654f 100644
>> --- a/include/linux/mmu_notifier.h
>> +++ b/include/linux/mmu_notifier.h
>> @@ -557,6 +557,19 @@ static inline void mmu_notifier_range_init_migrate(
>> __young; \
>> })
>>
>> +#define pudp_clear_flush_young_notify(__vma, __address, __pudp) \
>> +({ \
>> + int __young; \
>> + struct vm_area_struct *___vma = __vma; \
>> + unsigned long ___address = __address; \
>> + __young = pudp_clear_flush_young(___vma, ___address, __pudp); \
>> + __young |= mmu_notifier_clear_flush_young(___vma->vm_mm, \
>> + ___address, \
>> + ___address + \
>> + PUD_SIZE); \
>> + __young; \
>> +})
>> +
>> #define ptep_clear_young_notify(__vma, __address, __ptep) \
>> ({ \
>> int __young; \
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index 255275d5b73e..8ef358c386af 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -240,6 +240,20 @@ static inline int pmdp_clear_flush_young(struct vm_area_struct *vma,
>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>> #endif
>>
>> +#ifndef __HAVE_ARCH_PUDP_CLEAR_YOUNG_FLUSH
>> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>> +extern int pudp_clear_flush_young(struct vm_area_struct *vma,
>> + unsigned long address, pud_t *pudp);
>> +#else
>> +int pudp_clear_flush_young(struct vm_area_struct *vma,
>> + unsigned long address, pud_t *pudp)
>> +{
>> + BUILD_BUG();
>> + return 0;
>> +}
>> +#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>> +#endif
>> +
>> #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
>> static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>> unsigned long address,
>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>> index 3a6adfa70fb0..0af61dd193d2 100644
>> --- a/include/linux/rmap.h
>> +++ b/include/linux/rmap.h
>> @@ -206,6 +206,7 @@ struct page_vma_mapped_walk {
>> struct page *page;
>> struct vm_area_struct *vma;
>> unsigned long address;
>> + pud_t *pud;
>> pmd_t *pmd;
>> pte_t *pte;
>> spinlock_t *ptl;
>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>> index 5e77b269c330..d9d39ec06e21 100644
>> --- a/mm/page_vma_mapped.c
>> +++ b/mm/page_vma_mapped.c
>> @@ -145,9 +145,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> struct page *page = pvmw->page;
>> pgd_t *pgd;
>> p4d_t *p4d;
>> - pud_t *pud;
>> + pud_t pude;
>> pmd_t pmde;
>>
>> + if (!pvmw->pte && !pvmw->pmd && pvmw->pud)
>> + return not_found(pvmw);
>> +
>> /* The only possible pmd mapping has been handled on last iteration */
>> if (pvmw->pmd && !pvmw->pte)
>> return not_found(pvmw);
>> @@ -174,10 +177,31 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> p4d = p4d_offset(pgd, pvmw->address);
>> if (!p4d_present(*p4d))
>> return false;
>> - pud = pud_offset(p4d, pvmw->address);
>> - if (!pud_present(*pud))
>> + pvmw->pud = pud_offset(p4d, pvmw->address);
>> +
>> + /*
>> + * Make sure the pud value isn't cached in a register by the
>> + * compiler and used as a stale value after we've observed a
>> + * subsequent update.
>> + */
>> + pude = READ_ONCE(*pvmw->pud);
>> + if (pud_trans_huge(pude)) {
>> + pvmw->ptl = pud_lock(mm, pvmw->pud);
>> + if (likely(pud_trans_huge(*pvmw->pud))) {
>> + if (pvmw->flags & PVMW_MIGRATION)
>> + return not_found(pvmw);
>> + if (pud_page(*pvmw->pud) != page)
>> + return not_found(pvmw);
>> + return true;
>> + } else {
>> + /* THP pud was split under us: handle on pmd level */
>> + spin_unlock(pvmw->ptl);
>> + pvmw->ptl = NULL;
>
> Hm. What makes you sure the pmd table is established here?
>
> I have not looked at PUD THP handling of MADV_DONTNEED yet, but for PMD
> THP can became pmd_none() at any point (unless ptl is locked).
You are right. I need to check pud_present here and only
go to pmd level when pud is present, otherwise just return with not_found.
Thanks.
>
>> + }
>> + } else if (!pud_present(pude))
>> return false;
>> - pvmw->pmd = pmd_offset(pud, pvmw->address);
>> +
>> + pvmw->pmd = pmd_offset(pvmw->pud, pvmw->address);
>> /*
>> * Make sure the pmd value isn't cached in a register by the
>> * compiler and used as a stale value after we've observed a
>> @@ -213,6 +237,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> } else if (!pmd_present(pmde)) {
>> return false;
>> }
>> +
>> if (!map_pte(pvmw))
>> goto next_pte;
>> while (1) {
>> diff --git a/mm/rmap.c b/mm/rmap.c
>
> Why?
>
The extra newline? Will remove it.
>> index 10195a2421cf..77cec0658b76 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -803,9 +803,15 @@ static bool page_referenced_one(struct page *page, struct vm_area_struct *vma,
>> referenced++;
>> }
>> } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
>> - if (pmdp_clear_flush_young_notify(vma, address,
>> - pvmw.pmd))
>> - referenced++;
>> + if (pvmw.pmd) {
>> + if (pmdp_clear_flush_young_notify(vma, address,
>> + pvmw.pmd))
>> + referenced++;
>> + } else if (pvmw.pud) {
>> + if (pudp_clear_flush_young_notify(vma, address,
>> + pvmw.pud))
>> + referenced++;
>> + }
>> } else {
>> /* unexpected pmd-mapped page? */
>> WARN_ON_ONCE(1);
>> --
>> 2.28.0
>>
>>
>
> --
> Kirill A. Shutemov
—
Best Regards,
Yan Zi
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