On Fri, Aug 25, 2017 at 12:18:44PM +0300, Timofey Titovets wrote:
> Calculate byte set size for data sample:
> Calculate how many unique bytes has been in sample
> By count all bytes in bucket with count > 0
> If byte set low (~25%), data are easily compressible
>
> Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
> ---
> fs/btrfs/heuristic.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/fs/btrfs/heuristic.c b/fs/btrfs/heuristic.c
> index f1fa6e4f1c11..ef723e991576 100644
> --- a/fs/btrfs/heuristic.c
> +++ b/fs/btrfs/heuristic.c
> @@ -24,6 +24,7 @@
> #define ITER_SHIFT 256
> #define BUCKET_SIZE 256
> #define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED*READ_SIZE/ITER_SHIFT)
> +#define BYTE_SET_THRESHOLD 64
Explanation needed, partially covered by the changelog but we need to
see it in the code as well.
>
> struct bucket_item {
> u32 count;
> @@ -66,6 +67,27 @@ static struct list_head *heuristic_alloc_workspace(void)
> return ERR_PTR(-ENOMEM);
> }
>
> +static u32 byte_set_size(const struct workspace *ws)
> +{
> + u32 a = 0;
Please use 'i'.
> + u32 byte_set_size = 0;
> +
> + for (; a < BYTE_SET_THRESHOLD; a++) {
for (i = 0; ...)
> + if (ws->bucket[a].count > 0)
> + byte_set_size++;
> + }
> +
> + for (; a < BUCKET_SIZE; a++) {
So here the initialization is intentionally skipped, please add a
comment that this is expected or explain like "continue past the first
sample until ...".
> + if (ws->bucket[a].count > 0) {
> + byte_set_size++;
> + if (byte_set_size > BYTE_SET_THRESHOLD)
> + return byte_set_size;
> + }
> + }
> +
> + return byte_set_size;
> +}
> +
> static bool sample_repeated_patterns(struct workspace *ws)
> {
> u32 i = 0;
> @@ -138,6 +160,10 @@ static int heuristic(struct list_head *ws, struct inode *inode,
> workspace->bucket[byte].count++;
> }
>
> + a = byte_set_size(workspace);
> + if (a > BYTE_SET_THRESHOLD)
> + return 2;
> +
> return 1;
> }
>
> --
> 2.14.1
> --
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