linux-kernel - Re: [PATCH v4 1/6] userfaultfd: convert mfill_atomic_pte

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Message-ID: <765d450c-2ff6-1420-b94f-528d56bffee4@oracle.com>
Date:   Thu, 30 Mar 2023 10:02:52 -0700
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     Peng Zhang <zhangpeng362@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        willy@...radead.org, mike.kravetz@...cle.com
Cc:     vishal.moola@...il.com, muchun.song@...ux.dev,
        wangkefeng.wang@...wei.com, sunnanyong@...wei.com
Subject: Re: [PATCH v4 1/6] userfaultfd: convert mfill_atomic_pte_copy() to
 use a folio

On 3/30/23 6:40 AM, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@...wei.com>
> 
> Call vma_alloc_folio() directly instead of alloc_page_vma(). Add an
> assertion that this is a single-page folio and removes several calls to
> compound_head().
> 
> Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
> ---
>   mm/userfaultfd.c | 25 +++++++++++++------------
>   1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 7f1b5f8b712c..efa9e1d681ee 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -137,15 +137,15 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
>   {
>   	void *page_kaddr;
>   	int ret;
> -	struct page *page;
> +	struct folio *folio;
>   
>   	if (!*pagep) {
>   		ret = -ENOMEM;
> -		page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
> -		if (!page)
> +		folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma, dst_addr, false);
> +		if (!folio)
>   			goto out;
>   
> -		page_kaddr = kmap_local_page(page);
> +		page_kaddr = kmap_local_folio(folio, 0);

Should this variable name be kept as page_kaddr or should it be changed 
to something like folio_kaddr? kmap_local_folio() returns 
page_address(), so maybe page_kaddr is better.

>   		/*
>   		 * The read mmap_lock is held here.  Despite the
>   		 * mmap_lock being read recursive a deadlock is still
> @@ -171,36 +171,37 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
>   		/* fallback to copy_from_user outside mmap_lock */
>   		if (unlikely(ret)) {
>   			ret = -ENOENT;
> -			*pagep = page;
> +			*pagep = &folio->page;
>   			/* don't free the page */
>   			goto out;
>   		}
>   
> -		flush_dcache_page(page);
> +		flush_dcache_folio(folio);
>   	} else {
> -		page = *pagep;
> +		folio = page_folio(*pagep);
> +		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
>   		*pagep = NULL;
>   	}
>   
>   	/*
> -	 * The memory barrier inside __SetPageUptodate makes sure that
> +	 * The memory barrier inside __folio_mark_uptodate makes sure that
>   	 * preceding stores to the page contents become visible before
>   	 * the set_pte_at() write.
>   	 */
> -	__SetPageUptodate(page);
> +	__folio_mark_uptodate(folio);
>   
>   	ret = -ENOMEM;
> -	if (mem_cgroup_charge(page_folio(page), dst_vma->vm_mm, GFP_KERNEL))
> +	if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
>   		goto out_release;
>   
>   	ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
> -				       page, true, flags);
> +				       &folio->page, true, flags);
>   	if (ret)
>   		goto out_release;
>   out:
>   	return ret;
>   out_release:
> -	put_page(page);
> +	folio_put(folio);
>   	goto out;
>   }

Thanks,

Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>

>