linux-kernel - Re: [PATCH 17/19] dm: get rid of superfluous gfp flags

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Date:	Fri, 15 Apr 2016 08:29:28 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>, Shaohua Li <shli@...nel.org>
Subject: Re: [PATCH 17/19] dm: get rid of superfluous gfp flags



On Mon, 11 Apr 2016, Michal Hocko wrote:

> From: Michal Hocko <mhocko@...e.com>
> 
> copy_params seems to be little bit confused about which allocation flags
> to use. It enforces GFP_NOIO even though it uses
> memalloc_noio_{save,restore} which enforces GFP_NOIO at the page

memalloc_noio_{save,restore} is used because __vmalloc is flawed and 
doesn't respect GFP_NOIO properly (it doesn't use gfp flags when 
allocating pagetables).

The proper fix it to correct __vmalloc (though, it would require change to 
pagetable allocation routine on all architectures), not to remove GFP_NOIO 
from __vmalloc.

Mikulas

> allocator level automatically (via memalloc_noio_flags). It also
> uses __GFP_REPEAT for the __vmalloc request which doesn't make much
> sense either because vmalloc doesn't rely on costly high order
> allocations.
> 
> Cc: Shaohua Li <shli@...nel.org>
> Cc: Mikulas Patocka <mpatocka@...hat.com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  drivers/md/dm-ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 2adf81d81fca..dfe629a294e1 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1723,7 +1723,7 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
>  	if (!dmi) {
>  		unsigned noio_flag;
>  		noio_flag = memalloc_noio_save();
> -		dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL);
> +		dmi = __vmalloc(param_kernel->data_size, __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL);
>  		memalloc_noio_restore(noio_flag);
>  		if (dmi)
>  			*param_flags |= DM_PARAMS_VMALLOC;
> -- 
> 2.8.0.rc3
>