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Message-ID: <cbdd91ba-bfd4-2f6d-9f9f-9cdcc8ff81a4@nutanix.com>
Date: Mon, 27 Jun 2022 17:56:51 +0530
From: "manish.mishra" <manish.mishra@...anix.com>
To: James Houghton <jthoughton@...gle.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Muchun Song <songmuchun@...edance.com>,
Peter Xu <peterx@...hat.com>
Cc: David Hildenbrand <david@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
Jue Wang <juew@...gle.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 04/26] hugetlb: make huge_pte_lockptr take an explicit
shift argument.
On 24/06/22 11:06 pm, James Houghton wrote:
> This is needed to handle PTL locking with high-granularity mapping. We
> won't always be using the PMD-level PTL even if we're using the 2M
> hugepage hstate. It's possible that we're dealing with 4K PTEs, in which
> case, we need to lock the PTL for the 4K PTE.
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
> arch/powerpc/mm/pgtable.c | 3 ++-
> include/linux/hugetlb.h | 19 ++++++++++++++-----
> mm/hugetlb.c | 9 +++++----
> mm/migrate.c | 3 ++-
> mm/page_vma_mapped.c | 3 ++-
> 5 files changed, 25 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index e6166b71d36d..663d591a8f08 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -261,7 +261,8 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>
> psize = hstate_get_psize(h);
> #ifdef CONFIG_DEBUG_VM
> - assert_spin_locked(huge_pte_lockptr(h, vma->vm_mm, ptep));
> + assert_spin_locked(huge_pte_lockptr(huge_page_shift(h),
> + vma->vm_mm, ptep));
> #endif
>
> #else
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 498a4ae3d462..5fe1db46d8c9 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -868,12 +868,11 @@ static inline gfp_t htlb_modify_alloc_mask(struct hstate *h, gfp_t gfp_mask)
> return modified_mask;
> }
>
> -static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
> +static inline spinlock_t *huge_pte_lockptr(unsigned int shift,
> struct mm_struct *mm, pte_t *pte)
> {
> - if (huge_page_size(h) == PMD_SIZE)
> + if (shift == PMD_SHIFT)
> return pmd_lockptr(mm, (pmd_t *) pte);
> - VM_BUG_ON(huge_page_size(h) == PAGE_SIZE);
I may have wrong understanding here, is per pmd lock for reducing
contention, if that is the case should be take per pmd lock of
PAGE_SIZE too and page_table_lock for anything higer than PMD.
> return &mm->page_table_lock;
> }
>
> @@ -1076,7 +1075,7 @@ static inline gfp_t htlb_modify_alloc_mask(struct hstate *h, gfp_t gfp_mask)
> return 0;
> }
>
> -static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
> +static inline spinlock_t *huge_pte_lockptr(unsigned int shift,
> struct mm_struct *mm, pte_t *pte)
> {
> return &mm->page_table_lock;
> @@ -1116,7 +1115,17 @@ static inline spinlock_t *huge_pte_lock(struct hstate *h,
> {
> spinlock_t *ptl;
>
> - ptl = huge_pte_lockptr(h, mm, pte);
> + ptl = huge_pte_lockptr(huge_page_shift(h), mm, pte);
> + spin_lock(ptl);
> + return ptl;
> +}
> +
> +static inline spinlock_t *huge_pte_lock_shift(unsigned int shift,
> + struct mm_struct *mm, pte_t *pte)
> +{
> + spinlock_t *ptl;
> +
> + ptl = huge_pte_lockptr(shift, mm, pte);
> spin_lock(ptl);
> return ptl;
> }
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0eec34edf3b2..d6d0d4c03def 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4817,7 +4817,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> continue;
>
> dst_ptl = huge_pte_lock(h, dst, dst_pte);
> - src_ptl = huge_pte_lockptr(h, src, src_pte);
> + src_ptl = huge_pte_lockptr(huge_page_shift(h), src, src_pte);
> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
> entry = huge_ptep_get(src_pte);
> dst_entry = huge_ptep_get(dst_pte);
> @@ -4894,7 +4894,8 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
>
> /* Install the new huge page if src pte stable */
> dst_ptl = huge_pte_lock(h, dst, dst_pte);
> - src_ptl = huge_pte_lockptr(h, src, src_pte);
> + src_ptl = huge_pte_lockptr(huge_page_shift(h),
> + src, src_pte);
> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
> entry = huge_ptep_get(src_pte);
> if (!pte_same(src_pte_old, entry)) {
> @@ -4948,7 +4949,7 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr,
> pte_t pte;
>
> dst_ptl = huge_pte_lock(h, mm, dst_pte);
> - src_ptl = huge_pte_lockptr(h, mm, src_pte);
> + src_ptl = huge_pte_lockptr(huge_page_shift(h), mm, src_pte);
>
> /*
> * We don't have to worry about the ordering of src and dst ptlocks
> @@ -6024,7 +6025,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> page_in_pagecache = true;
> }
>
> - ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
> + ptl = huge_pte_lockptr(huge_page_shift(h), dst_mm, dst_pte);
> spin_lock(ptl);
>
> /*
> diff --git a/mm/migrate.c b/mm/migrate.c
> index e51588e95f57..a8a960992373 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -318,7 +318,8 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> void migration_entry_wait_huge(struct vm_area_struct *vma,
> struct mm_struct *mm, pte_t *pte)
> {
> - spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
> + spinlock_t *ptl = huge_pte_lockptr(huge_page_shift(hstate_vma(vma)),
> + mm, pte);
> __migration_entry_wait(mm, pte, ptl);
> }
>
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index c10f839fc410..8921dd4e41b1 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -174,7 +174,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> if (!pvmw->pte)
> return false;
>
> - pvmw->ptl = huge_pte_lockptr(hstate, mm, pvmw->pte);
> + pvmw->ptl = huge_pte_lockptr(huge_page_shift(hstate),
> + mm, pvmw->pte);
> spin_lock(pvmw->ptl);
> if (!check_pte(pvmw))
> return not_found(pvmw);
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