linux-kernel - Re: [PATCH] gfs2: use __vmalloc GFP

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Date:	Mon, 2 Feb 2015 16:37:08 +1100
From:	Dave Chinner <david@...morbit.com>
To:	green@...uxhacker.ru
Cc:	Steven Whitehouse <swhiteho@...hat.com>, cluster-devel@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gfs2: use __vmalloc GFP_NOFS for fs-related allocations.

On Sun, Feb 01, 2015 at 10:59:54PM -0500, green@...uxhacker.ru wrote:
> From: Oleg Drokin <green@...uxhacker.ru>
> 
> leaf_dealloc uses vzalloc as a fallback to kzalloc(GFP_NOFS), so
> it clearly does not want any shrinker activity within the fs itself.
> convert vzalloc into __vmalloc(GFP_NOFS|__GFP_ZERO) to better achieve
> this goal.
> 
> Signed-off-by: Oleg Drokin <green@...uxhacker.ru>
> ---
>  fs/gfs2/dir.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
> index c5a34f0..6371192 100644
> --- a/fs/gfs2/dir.c
> +++ b/fs/gfs2/dir.c
> @@ -1896,7 +1896,8 @@ static int leaf_dealloc(struct gfs2_inode *dip, u32 index, u32 len,
>  
>  	ht = kzalloc(size, GFP_NOFS | __GFP_NOWARN);
>  	if (ht == NULL)
> -		ht = vzalloc(size);
> +		ht = __vmalloc(size, GFP_NOFS | __GFP_NOWARN | __GFP_ZERO,
> +			       PAGE_KERNEL);

That, in the end, won't help as vmalloc still uses GFP_KERNEL
allocations deep down in the PTE allocation code. See the hacks in
the DM and XFS code to work around this. i.e. go look for callers of
memalloc_noio_save().  It's ugly and grotesque, but we've got no
other way to limit reclaim context because the MM devs won't pass
the vmalloc gfp context down the stack to the PTE allocations....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
--
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