linux-kernel - Re: [PATCH v4 63/66] i915: Use the VMA iterator

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Date:   Thu, 20 Jan 2022 15:59:11 +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 63/66] i915: Use the VMA iterator

On 12/1/21 15:30, Liam Howlett wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> Replace the O(n.log(n)) loop with an O(n) loop.

Not true?

> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> index 3173c9f9a040..39960973c130 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> @@ -425,12 +425,11 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
>  static int
>  probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
>  {
> -	const unsigned long end = addr + len;
> +	VMA_ITERATOR(vmi, mm, addr);
>  	struct vm_area_struct *vma;
> -	int ret = -EFAULT;
>  
>  	mmap_read_lock(mm);
> -	for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
> +	for_each_vma_range(vmi, vma, addr + len) {
>  		/* Check for holes, note that we also update the addr below */
>  		if (vma->vm_start > addr)
>  			break;
> @@ -438,16 +437,13 @@ probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
>  		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
>  			break;
>  
> -		if (vma->vm_end >= end) {
> -			ret = 0;
> -			break;
> -		}
> -
>  		addr = vma->vm_end;
>  	}
>  	mmap_read_unlock(mm);
>  
> -	return ret;
> +	if (vma)
> +		return -EFAULT;
> +	return 0;
>  }
>  
>  /*