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Date:   Fri, 2 Jun 2023 10:47:37 -0700
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Subject: Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()
Content-Language: en-US
To:     Peng Zhang <zhangpeng362@huawei.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        willy@infradead.org, mike.kravetz@oracle.com
Cc:     muchun.song@linux.dev, vishal.moola@gmail.com,
        wangkefeng.wang@huawei.com, sunnanyong@huawei.com
References: <20230602015408.376149-1-zhangpeng362@huawei.com>
 <20230602015408.376149-3-zhangpeng362@huawei.com>
From:   Sidhartha Kumar <sidhartha.kumar@oracle.com>
In-Reply-To: <20230602015408.376149-3-zhangpeng362@huawei.com>
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On 6/1/23 6:54 PM, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> We can replace nine implict calls to compound_head() with one by using
> old_folio. However, we still need to keep old_page because we need to
> know which page in the folio we are copying.
> 
> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
> ---
>   mm/hugetlb.c | 22 ++++++++++++----------
>   1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0b774dd3d57b..f0ab6e8adf6f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5543,6 +5543,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	pte_t pte = huge_ptep_get(ptep);
>   	struct hstate *h = hstate_vma(vma);
>   	struct page *old_page;
> +	struct folio *old_folio;
>   	struct folio *new_folio;
>   	int outside_reserve = 0;
>   	vm_fault_t ret = 0;
> @@ -5574,6 +5575,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	}
>   
>   	old_page = pte_page(pte);
> +	old_folio = page_folio(old_page);
>   
>   	delayacct_wpcopy_start();
>   
> @@ -5582,7 +5584,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * If no-one else is actually using this page, we're the exclusive
>   	 * owner and can reuse this page.
>   	 */
> -	if (page_mapcount(old_page) == 1 && PageAnon(old_page)) {
> +	if (page_mapcount(old_page) == 1 && folio_test_anon(old_folio)) {
>   		if (!PageAnonExclusive(old_page))
>   			page_move_anon_rmap(old_page, vma);
>   		if (likely(!unshare))
> @@ -5591,8 +5593,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		delayacct_wpcopy_end();
>   		return 0;
>   	}
> -	VM_BUG_ON_PAGE(PageAnon(old_page) && PageAnonExclusive(old_page),
> -		       old_page);
> +	VM_BUG_ON_PAGE(folio_test_anon(old_folio) &&
> +		       PageAnonExclusive(old_page), old_page);
>   
>   	/*
>   	 * If the process that created a MAP_PRIVATE mapping is about to
> @@ -5604,10 +5606,10 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * of the full address range.
>   	 */
>   	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
> -			page_folio(old_page) != pagecache_folio)
> +			old_folio != pagecache_folio)
>   		outside_reserve = 1;
>   
> -	get_page(old_page);
> +	folio_get(old_folio);
>   
>   	/*
>   	 * Drop page table lock as buddy allocator may be called. It will
> @@ -5629,7 +5631,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   			pgoff_t idx;
>   			u32 hash;
>   
> -			put_page(old_page);
> +			folio_put(old_folio);
>   			/*
>   			 * Drop hugetlb_fault_mutex and vma_lock before
>   			 * unmapping.  unmapping needs to hold vma_lock
> @@ -5674,7 +5676,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		goto out_release_all;
>   	}
>   
> -	if (copy_user_large_folio(new_folio, page_folio(old_page), address, vma)) {
> +	if (copy_user_large_folio(new_folio, old_folio, address, vma)) {
>   		ret = VM_FAULT_HWPOISON_LARGE;
>   		goto out_release_all;
>   	}
> @@ -5703,7 +5705,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		set_huge_pte_at(mm, haddr, ptep, newpte);
>   		folio_set_hugetlb_migratable(new_folio);
>   		/* Make the old page be freed below */
> -		new_folio = page_folio(old_page);
> +		new_folio = old_folio;
>   	}
>   	spin_unlock(ptl);
>   	mmu_notifier_invalidate_range_end(&range);
> @@ -5712,11 +5714,11 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * No restore in case of successful pagetable update (Break COW or
>   	 * unshare)
>   	 */
> -	if (new_folio != page_folio(old_page))
> +	if (new_folio != old_folio)
>   		restore_reserve_on_error(h, vma, haddr, new_folio);
>   	folio_put(new_folio);
>   out_release_old:
> -	put_page(old_page);
> +	folio_put(old_folio);
>   
>   	spin_lock(ptl); /* Caller expects lock to be held */
>   
Reviewed-by Sidhartha Kumar <sidhartha.kumar@oracle.com>