pack-objects: shrink z_delta_size field in struct object_entry

We only cache deltas when it's smaller than a certain limit. This limit
defaults to 1000 but save its compressed length in a 64-bit field.
Shrink that field down to 20 bits, so you can only cache 1MB deltas.
Larger deltas must be recomputed at when the pack is written down.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d97f10722c1683b08d1ef312525c9513c4310d1d..a62134264e34b4bff1a492f67633d6fa7ead7c00 100644 (file)
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2459,7 +2459,8 @@ pack.deltaCacheLimit::
        The maximum size of a delta, that is cached in
        linkgit:git-pack-objects[1]. This cache is used to speed up the
        writing object phase by not having to recompute the final delta
-       result once the best match for all objects is found. Defaults to 1000.
+       result once the best match for all objects is found.
+       Defaults to 1000. Maximum value is 65535.
 
 pack.threads::
        Specifies the number of threads to spawn when searching for best

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index ec02641d2e773841ed85541d696a711cd34fee11..211bb1ad0efc047db77749b193a21b892623aead 100644 (file)
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2099,12 +2099,19 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
                 * between writes at that moment.
                 */
                if (entry->delta_data && !pack_to_stdout) {
-                       entry->z_delta_size = do_compress(&entry->delta_data,
-                                                         entry->delta_size);
-                       cache_lock();
-                       delta_cache_size -= entry->delta_size;
-                       delta_cache_size += entry->z_delta_size;
-                       cache_unlock();
+                       unsigned long size;
+
+                       size = do_compress(&entry->delta_data, entry->delta_size);
+                       if (size < (1U << OE_Z_DELTA_BITS)) {
+                               entry->z_delta_size = size;
+                               cache_lock();
+                               delta_cache_size -= entry->delta_size;
+                               delta_cache_size += entry->z_delta_size;
+                               cache_unlock();
+                       } else {
+                               FREE_AND_NULL(entry->delta_data);
+                               entry->z_delta_size = 0;
+                       }
                }
 
                /* if we made n a delta, and if n is already at max
@@ -3087,6 +3094,11 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
                        depth, (1 << OE_DEPTH_BITS) - 1);
                depth = (1 << OE_DEPTH_BITS) - 1;
        }
+       if (cache_max_small_delta_size >= (1U << OE_Z_DELTA_BITS)) {
+               warning(_("pack.deltaCacheLimit is too high, forcing %d"),
+                       (1U << OE_Z_DELTA_BITS) - 1);
+               cache_max_small_delta_size = (1U << OE_Z_DELTA_BITS) - 1;
+       }
 
        argv_array_push(&rp, "pack-objects");
        if (thin) {

diff --git a/pack-objects.h b/pack-objects.h
index e962dce3c05be345bf0184d76d3ea3b7be190885..9d0391c1739e58c9ed8dd18d98362561c53477d4 100644 (file)
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -6,6 +6,7 @@
 #define OE_DFS_STATE_BITS      2
 #define OE_DEPTH_BITS          12
 #define OE_IN_PACK_BITS                10
+#define OE_Z_DELTA_BITS                20
 
 /*
  * State flags for depth-first search used for analyzing delta cycles.
@@ -77,7 +78,7 @@ struct object_entry {
                                     */
        void *delta_data;       /* cached delta (uncompressed) */
        unsigned long delta_size;       /* delta data size (uncompressed) */
-       unsigned long z_delta_size;     /* delta data size (compressed) */
+       unsigned z_delta_size:OE_Z_DELTA_BITS;
        unsigned type_:TYPE_BITS;
        unsigned in_pack_type:TYPE_BITS; /* could be delta */
        unsigned type_valid:1;