linux-kernel - Re: [PATCH] mm: Refactor vma_map_pages to use vm_insert

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Message-ID: <CADyq12wpDTjHVGs7CTQ3SPNMO_ovmMk-rN7L4i_AGvdoLYQLnA@mail.gmail.com>
Date: Wed, 28 Jan 2026 17:59:12 -0500
From: Brian Geffon <bgeffon@...gle.com>
To: Justin Green <greenjustin@...omium.org>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, david@...nel.org, 
	lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz, 
	rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, 
	linux-kernel@...r.kernel.org, greenjustin@...gle.com, rientjes@...gle.com, 
	arjunroy@...gle.com
Subject: Re: [PATCH] mm: Refactor vma_map_pages to use vm_insert_pages

On Wed, Jan 28, 2026 at 5:57 PM Justin Green <greenjustin@...omium.org> wrote:
>
> vma_map_pages currently calls vm_insert_page on each individual page in
> the mapping, which creates significant overhead because we are
> repeatedly spinlocking. Instead, we should batch insert pages using
> vm_insert_pages, which amortizes the cost of the spinlock.

This makes sense, I wonder why this wasn't done previously?

>
> Tested through watching hardware accelerated video on a MTK ChromeOS
> device. This particular path maps both a V4L2 buffer and a GEM allocated
> buffer into userspace and converts the contents from one pixel format to
> another. Both vb2_mmap() and mtk_gem_object_mmap() exercise this
> pathway.
>
> Signed-off-by: Justin Green <greenjustin@...omium.org>

Acked-by: Brian Geffon <bgeffon@...gle.com>

> ---
>  mm/memory.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index da360a6eb8a4..7ae6ac42e7d8 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2499,7 +2499,6 @@ static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
>  {
>         unsigned long count = vma_pages(vma);
>         unsigned long uaddr = vma->vm_start;
> -       int ret, i;
>
>         /* Fail if the user requested offset is beyond the end of the object */
>         if (offset >= num)
> @@ -2509,14 +2508,7 @@ static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
>         if (count > num - offset)
>                 return -ENXIO;
>
> -       for (i = 0; i < count; i++) {
> -               ret = vm_insert_page(vma, uaddr, pages[offset + i]);
> -               if (ret < 0)
> -                       return ret;
> -               uaddr += PAGE_SIZE;
> -       }
> -
> -       return 0;
> +       return vm_insert_pages(vma, uaddr, pages + offset, &count);
>  }
>
>  /**
> --
> 2.53.0.rc1.217.geba53bf80e-goog
>