On Mon, Jul 24, 2017 at 02:37:06PM +0300, Timofey Titovets wrote:
> Get small sample from input data
> and calculate byte type count for that sample
>
> Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
> ---
> fs/btrfs/compression.c | 24 ++++++++++++++++++++++--
> fs/btrfs/compression.h | 11 +++++++++++
> 2 files changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 63f54bd2d5bb..1501d4fe90cc 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -1068,15 +1068,35 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
> u64 index = start >> PAGE_SHIFT;
> u64 end_index = end >> PAGE_SHIFT;
> struct page *page;
> - int ret = 1;
> + struct heuristic_bucket_item *bucket;
> + int a, b, ret;
> + u8 symbol, *input_data;
> +
> + ret = 1;
> +
> + bucket = kcalloc(BTRFS_HEURISTIC_BUCKET_SIZE,
> + sizeof(struct heuristic_bucket_item), GFP_NOFS);
> +
> + if (!bucket)
> + goto out;
>
> while (index <= end_index) {
> page = find_get_page(inode->i_mapping, index);
> - kmap(page);
> + input_data = kmap(page);
> + a = 0;
> + while (a < PAGE_SIZE) {
> + for (b = 0; b < BTRFS_HEURISTIC_READ_SIZE; b++) {
> + symbol = input_data[a+b];
> + bucket[symbol].count++;
> + }
> + a += BTRFS_HEURISTIC_ITERATOR_OFFSET;
> + }
> kunmap(page);
> put_page(page);
> index++;
> }
>
> +out:
> + kfree(bucket);
> return ret;
> }
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index d1f4eee2d0af..984943e5e1ae 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -129,6 +129,17 @@ struct btrfs_compress_op {
> extern const struct btrfs_compress_op btrfs_zlib_compress;
> extern const struct btrfs_compress_op btrfs_lzo_compress;
>
> +struct heuristic_bucket_item {
> + u8 padding;
> + u8 symbol;
> + u16 count;
> +};
> +
> +#define BTRFS_HEURISTIC_READ_SIZE 16
> +#define BTRFS_HEURISTIC_READS_PER_PAGE 8*PAGE_SIZE/4096
I hate magic numbers, why is this 8*PAGE_SIZE/4096? If you want to check every
512 bytes why not just set BTRFS_HEURISTIC_ITERATOR_OFFSET to 512? That makes
it easier to understand what you are trying to accomplish. Thanks,
Josef
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
