linux-kernel - Re: [PATCH v2 1/9] mm: introduce pmd

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Message-ID: <edd82170-7149-1abf-6204-f1d665a5fca2@redhat.com>
Date:   Tue, 24 Aug 2021 18:26:42 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>, akpm@...ux-foundation.org,
        tglx@...utronix.de, hannes@...xchg.org, mhocko@...nel.org,
        vdavydov.dev@...il.com, kirill.shutemov@...ux.intel.com,
        mika.penttila@...tfour.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, songmuchun@...edance.com
Subject: Re: [PATCH v2 1/9] mm: introduce pmd_install() helper

On 19.08.21 05:18, Qi Zheng wrote:
> Currently we have three times the same few lines repeated in the
> code. Deduplicate them by newly introduced pmd_install() helper.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>   include/linux/mm.h |  1 +
>   mm/filemap.c       | 11 ++---------
>   mm/memory.c        | 34 ++++++++++++++++------------------
>   3 files changed, 19 insertions(+), 27 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ce8fc0fd6d6e..57e48217bd71 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2471,6 +2471,7 @@ static inline spinlock_t *pud_lock(struct mm_struct *mm, pud_t *pud)
>   	return ptl;
>   }
>   
> +extern void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte);
>   extern void __init pagecache_init(void);
>   extern void __init free_area_init_memoryless_node(int nid);
>   extern void free_initmem(void);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 53913fced7ae..9f773059c6dc 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3210,15 +3210,8 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
>   	    }
>   	}
>   
> -	if (pmd_none(*vmf->pmd)) {
> -		vmf->ptl = pmd_lock(mm, vmf->pmd);
> -		if (likely(pmd_none(*vmf->pmd))) {
> -			mm_inc_nr_ptes(mm);
> -			pmd_populate(mm, vmf->pmd, vmf->prealloc_pte);
> -			vmf->prealloc_pte = NULL;
> -		}
> -		spin_unlock(vmf->ptl);
> -	}
> +	if (pmd_none(*vmf->pmd))
> +		pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
>   
>   	/* See comment in handle_pte_fault() */
>   	if (pmd_devmap_trans_unstable(vmf->pmd)) {
> diff --git a/mm/memory.c b/mm/memory.c
> index 39e7a1495c3c..ef7b1762e996 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -433,9 +433,20 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   	}
>   }
>   
> +void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte)
> +{
> +	spinlock_t *ptl = pmd_lock(mm, pmd);
> +
> +	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
> +		mm_inc_nr_ptes(mm);
> +		pmd_populate(mm, pmd, *pte);
> +		*pte = NULL;
> +	}
> +	spin_unlock(ptl);
> +}
> +
>   int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
>   {
> -	spinlock_t *ptl;
>   	pgtable_t new = pte_alloc_one(mm);
>   	if (!new)
>   		return -ENOMEM;
> @@ -455,13 +466,7 @@ int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
>   	 */
>   	smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
>   
> -	ptl = pmd_lock(mm, pmd);
> -	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
> -		mm_inc_nr_ptes(mm);
> -		pmd_populate(mm, pmd, new);
> -		new = NULL;
> -	}
> -	spin_unlock(ptl);
> +	pmd_install(mm, pmd, &new);
>   	if (new)
>   		pte_free(mm, new);
>   	return 0;
> @@ -4027,17 +4032,10 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>   				return ret;
>   		}
>   
> -		if (vmf->prealloc_pte) {
> -			vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
> -			if (likely(pmd_none(*vmf->pmd))) {
> -				mm_inc_nr_ptes(vma->vm_mm);
> -				pmd_populate(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
> -				vmf->prealloc_pte = NULL;
> -			}
> -			spin_unlock(vmf->ptl);
> -		} else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd))) {
> +		if (vmf->prealloc_pte)
> +			pmd_install(vma->vm_mm, vmf->pmd, &vmf->prealloc_pte);
> +		else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd)))
>   			return VM_FAULT_OOM;
> -		}
>   	}
>   
>   	/* See comment in handle_pte_fault() */
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

That's mostly unrelated to the remaining part of the series and can be 
picked up early.

-- 
Thanks,

David / dhildenb