Date:   Mon, 6 Mar 2023 20:03:25 -0500
From:   Peter Xu <peterx@redhat.com>
To:     Axel Rasmussen <axelrasmussen@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        Muchun Song <muchun.song@linux.dev>,
        Nadav Amit <namit@vmware.com>, Shuah Khan <shuah@kernel.org>,
        James Houghton <jthoughton@google.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 2/5] mm: userfaultfd: don't pass around both mm and vma
Message-ID: <ZAaNXTXs5ey4QYTl@x1n>
References: <20230306225024.264858-1-axelrasmussen@google.com>
 <20230306225024.264858-3-axelrasmussen@google.com>
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On Mon, Mar 06, 2023 at 02:50:21PM -0800, Axel Rasmussen wrote:
> Quite a few userfaultfd functions took both mm and vma pointers as
> arguments. Since the mm is trivially accessible via vma->vm_mm, there's
> no reason to pass both; it just needlessly extends the already long
> argument list.
> 
> Get rid of the mm pointer, where possible, to shorten the argument list.
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>

Acked-by: Peter Xu <peterx@redhat.com>

One nit below:

> @@ -6277,7 +6276,7 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
>  		folio_in_pagecache = true;
>  	}
>  
> -	ptl = huge_pte_lock(h, dst_mm, dst_pte);
> +	ptl = huge_pte_lock(h, dst_vma->vm_mm, dst_pte);
>  
>  	ret = -EIO;
>  	if (folio_test_hwpoison(folio))
> @@ -6319,9 +6318,9 @@ int hugetlb_mfill_atomic_pte(struct mm_struct *dst_mm,
>  	if (wp_copy)
>  		_dst_pte = huge_pte_mkuffd_wp(_dst_pte);
>  
> -	set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
> +	set_huge_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
>  
> -	hugetlb_count_add(pages_per_huge_page(h), dst_mm);
> +	hugetlb_count_add(pages_per_huge_page(h), dst_vma->vm_mm);

When vm_mm referenced multiple times (say, >=3?), let's still cache it in a
temp var?

I'm not sure whether compiler is smart enough to already do that with a
reg, even if so it may slightly improve readability too, imho, by avoiding
the multiple but same indirection for the reader.

Thanks,

-- 
Peter Xu