linux-kernel - Re: [PATCH v4 50/66] mm/gup: Use maple tree navigation instead of linked list

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Date:   Wed, 19 Jan 2022 18:39:16 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 50/66] mm/gup: Use maple tree navigation instead of
 linked list

On 12/1/21 15:30, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

Empty message.

> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
>  mm/gup.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 2c51e9748a6a..60892e5df6a2 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1570,7 +1570,6 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
>  	long ret = 0;
>  
>  	end = start + len;
> -
>  	for (nstart = start; nstart < end; nstart = nend) {
>  		/*
>  		 * We want to fault in pages for [nstart; end) address range.
> @@ -1579,10 +1578,10 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
>  		if (!locked) {
>  			locked = 1;
>  			mmap_read_lock(mm);
> -			vma = find_vma(mm, nstart);
> +			vma = find_vma_intersection(mm, start, end);

Is it ok to use start instead of nstart? At least theoretically,
populate_vma_page_range() called later can reset locked to 0, so !locked
doesn't guarantee we are in the first iteration?

>  		} else if (nstart >= vma->vm_end)
> -			vma = vma->vm_next;
> -		if (!vma || vma->vm_start >= end)
> +			vma = find_vma(mm, vma->vm_end);
> +		if (!vma)
>  			break;
>  		/*
>  		 * Set [nstart; nend) to intersection of desired address