[PATCH v6 2/6] Btrfs: heuristic workspace add bucket and sample items

[Timofey Titovets]

Heuristic workspace:
 - Add bucket for storing byte type counters
 - Add sample array for storing partial copy of
   input data range
 - Add counter for store current sample size to workspace

Signed-off-by: Timofey Titovets <nefelim...@gmail.com>
---
 fs/btrfs/heuristic.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/fs/btrfs/heuristic.c b/fs/btrfs/heuristic.c
index d0e9f9112b7e..9a212674f527 100644
--- a/fs/btrfs/heuristic.c
+++ b/fs/btrfs/heuristic.c
@@ -20,13 +20,29 @@
 #include <linux/bio.h>
 #include "compression.h"

+#define READ_SIZE 16
+#define ITER_SHIFT 256
+#define BUCKET_SIZE 256
+#define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED*READ_SIZE/ITER_SHIFT)
+
+struct bucket_item {
+       u32 count;
+};
+
 struct workspace {
+       u8  *sample;
+       /* Partial copy of input data */
+       u32 sample_size;
+       /* Bucket store counter for each byte type */
+       struct bucket_item bucket[BUCKET_SIZE];
        struct list_head list;
 };

 static void heuristic_free_workspace(struct list_head *ws)
 {
        struct workspace *workspace = list_entry(ws, struct workspace, list);
+
+       kvfree(workspace->sample);
        kfree(workspace);
 }

@@ -38,9 +54,16 @@ static struct list_head *heuristic_alloc_workspace(void)
        if (!workspace)
                return ERR_PTR(-ENOMEM);

+       workspace->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
+       if (!workspace->sample)
+               goto fail;
+
        INIT_LIST_HEAD(&workspace->list);

        return &workspace->list;
+fail:
+       heuristic_free_workspace(&workspace->list);
+       return ERR_PTR(-ENOMEM);
 }

 static int heuristic(struct list_head *ws, struct inode *inode,
--
2.14.1
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