linux-kernel - Re: [PATCH] [media] v4l: vb2-memops: use vma slab when vma allocation

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Date:	Wed, 08 Apr 2015 18:01:02 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Cho KyongHo <pullip.cho@...sung.com>, linux-media@...r.kernel.org,
	laurent.pinchart@...asonboard.com, linux-kernel@...r.kernel.org,
	mchehab@....samsung.com
CC:	hans.verkuil@...co.com
Subject: Re: [PATCH] [media] v4l: vb2-memops: use vma slab when vma allocation

Mauro,

Please revert this patch: vm_area_cachep is not exported, so you cannot use this
in a module.

Cho KyongHo, if you believe that vm_area_cachep should be exported so it can be
used here, then please make a patch for that.

For the time being though, this patch should be reverted.

This patch slipped through the cracks and I clearly never reviewed it, and I only
noticed the problem after I compiled the media_tree git repo after this patch
was merged.

Regards,

	Hans

On 02/05/2015 06:52 AM, Cho KyongHo wrote:
> The slab for vm_area_struct which is vm_area_cachep is already prepared
> for the general use. Instead of kmalloc() for the vma copy for userptr,
> allocation from vm_area_cachep is more beneficial.
> 
> CC: Mauro Carvalho Chehab <mchehab@....samsung.com>
> CC: Hans Verkuil <hans.verkuil@...co.com>
> CC: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Cho KyongHo <pullip.cho@...sung.com>
> ---
>  drivers/media/v4l2-core/videobuf2-memops.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-memops.c b/drivers/media/v4l2-core/videobuf2-memops.c
> index 81c1ad8..dd06efa 100644
> --- a/drivers/media/v4l2-core/videobuf2-memops.c
> +++ b/drivers/media/v4l2-core/videobuf2-memops.c
> @@ -37,7 +37,7 @@ struct vm_area_struct *vb2_get_vma(struct vm_area_struct *vma)
>  {
>  	struct vm_area_struct *vma_copy;
>  
> -	vma_copy = kmalloc(sizeof(*vma_copy), GFP_KERNEL);
> +	vma_copy = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
>  	if (vma_copy == NULL)
>  		return NULL;
>  
> @@ -75,7 +75,7 @@ void vb2_put_vma(struct vm_area_struct *vma)
>  	if (vma->vm_file)
>  		fput(vma->vm_file);
>  
> -	kfree(vma);
> +	kmem_cache_free(vm_area_cachep, vma);
>  }
>  EXPORT_SYMBOL_GPL(vb2_put_vma);
>  
> 

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