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SubjectRe: [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@cn.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@redhat.com>

Thanks,

Josef


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