linux-kernel - Re: [PATCH 1/6] btrfs: fix threshold calculation for block groups smaller than 1GB

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Date:	Mon, 23 Aug 2010 09:02:25 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Josef Bacik <josef@...hat.com>, linux-btrfs@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] btrfs: fix threshold calculation for block groups
	smaller than 1GB

On Mon, Aug 23, 2010 at 09:22:40AM +0800, Li Zefan wrote:
> If a block group is smaller than 1GB, the extent entry threadhold
> calculation will always set the threshold to 0.
> 
> So as free space gets fragmented, btrfs will switch to use bitmap
> to manage free space, but then will never switch back to extents
> due to this bug.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  fs/btrfs/free-space-cache.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index f488fac..7edbef6 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -263,14 +263,18 @@ static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
>  	u64 max_bytes;
>  	u64 bitmap_bytes;
>  	u64 extent_bytes;
> +	u64 size = block_group->key.offset;
>  
>  	/*
>  	 * The goal is to keep the total amount of memory used per 1gb of space
>  	 * at or below 32k, so we need to adjust how much memory we allow to be
>  	 * used by extent based free space tracking
>  	 */
> -	max_bytes = MAX_CACHE_BYTES_PER_GIG *
> -		(div64_u64(block_group->key.offset, 1024 * 1024 * 1024));
> +	if (size < 1024 * 1024 * 1024)
> +		max_bytes = MAX_CACHE_BYTES_PER_GIG;
> +	else
> +		max_bytes = MAX_CACHE_BYTES_PER_GIG *
> +			div64_u64(size, 1024 * 1024 * 1024);
>  
>  	/*
>  	 * we want to account for 1 more bitmap than what we have so we can make
> -- 
> 1.7.0.1
> 

Reviewed-by: Josef Bacik <josef@...hat.com>

Thanks,

Josef
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