pack-objects: move in_pack out of struct object_entry

Instead of using 8 bytes (on 64 bit arch) to store a pointer to a
pack. Use an index instead since the number of packs should be
relatively small.

This limits the number of packs we can handle to 1k. Since we can't be
sure people can never run into the situation where they have more than
1k pack files. Provide a fall back route for it.

If we find out they have too many packs, the new in_pack_by_idx[]
array (which has at most 1k elements) will not be used. Instead we
allocate in_pack[] array that holds nr_objects elements. This is
similar to how the optional in_pack_pos field is handled.

The new simple test is just to make sure the too-many-packs code path
is at least executed. The true test is running

make test GIT_TEST_FULL_IN_PACK_ARRAY=1

to take advantage of other special case tests.

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

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index d9c89e87cd29e39e3d647e450c296307ce4750c9..2784d58ec22ff7d0550178bfd50d938d4ba990f1 100644 (file)
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -31,6 +31,8 @@
 #include "packfile.h"
 #include "object-store.h"
 
+#define IN_PACK(obj) oe_in_pack(&to_pack, obj)
+
 static const char *pack_usage[] = {
        N_("git pack-objects --stdout [<options>...] [< <ref-list> | < <object-list>]"),
        N_("git pack-objects [<options>...] <base-name> [< <ref-list> | < <object-list>]"),
@@ -367,7 +369,7 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
                                unsigned long limit, int usable_delta)
 {
-       struct packed_git *p = entry->in_pack;
+       struct packed_git *p = IN_PACK(entry);
        struct pack_window *w_curs = NULL;
        struct revindex_entry *revidx;
        off_t offset;
@@ -478,7 +480,7 @@ static off_t write_object(struct hashfile *f,
 
        if (!reuse_object)
                to_reuse = 0;   /* explicit */
-       else if (!entry->in_pack)
+       else if (!IN_PACK(entry))
                to_reuse = 0;   /* can't reuse what we don't have */
        else if (oe_type(entry) == OBJ_REF_DELTA ||
                 oe_type(entry) == OBJ_OFS_DELTA)
@@ -1074,7 +1076,7 @@ static void create_object_entry(const struct object_id *oid,
        else
                nr_result++;
        if (found_pack) {
-               entry->in_pack = found_pack;
+               oe_set_in_pack(&to_pack, entry, found_pack);
                entry->in_pack_offset = found_offset;
        }
 
@@ -1399,8 +1401,8 @@ static void cleanup_preferred_base(void)
 
 static void check_object(struct object_entry *entry)
 {
-       if (entry->in_pack) {
-               struct packed_git *p = entry->in_pack;
+       if (IN_PACK(entry)) {
+               struct packed_git *p = IN_PACK(entry);
                struct pack_window *w_curs = NULL;
                const unsigned char *base_ref = NULL;
                struct object_entry *base_entry;
@@ -1535,14 +1537,16 @@ static int pack_offset_sort(const void *_a, const void *_b)
 {
        const struct object_entry *a = *(struct object_entry **)_a;
        const struct object_entry *b = *(struct object_entry **)_b;
+       const struct packed_git *a_in_pack = IN_PACK(a);
+       const struct packed_git *b_in_pack = IN_PACK(b);
 
        /* avoid filesystem trashing with loose objects */
-       if (!a->in_pack && !b->in_pack)
+       if (!a_in_pack && !b_in_pack)
                return oidcmp(&a->idx.oid, &b->idx.oid);
 
-       if (a->in_pack < b->in_pack)
+       if (a_in_pack < b_in_pack)
                return -1;
-       if (a->in_pack > b->in_pack)
+       if (a_in_pack > b_in_pack)
                return 1;
        return a->in_pack_offset < b->in_pack_offset ? -1 :
                        (a->in_pack_offset > b->in_pack_offset);
@@ -1578,7 +1582,7 @@ static void drop_reused_delta(struct object_entry *entry)
 
        oi.sizep = &entry->size;
        oi.typep = &type;
-       if (packed_object_info(entry->in_pack, entry->in_pack_offset, &oi) < 0) {
+       if (packed_object_info(IN_PACK(entry), entry->in_pack_offset, &oi) < 0) {
                /*
                 * We failed to get the info from this pack for some reason;
                 * fall back to sha1_object_info, which may find another copy.
@@ -1848,8 +1852,8 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
         * it, we will still save the transfer cost, as we already know
         * the other side has it and we won't send src_entry at all.
         */
-       if (reuse_delta && trg_entry->in_pack &&
-           trg_entry->in_pack == src_entry->in_pack &&
+       if (reuse_delta && IN_PACK(trg_entry) &&
+           IN_PACK(trg_entry) == IN_PACK(src_entry) &&
            !src_entry->preferred_base &&
            trg_entry->in_pack_type != OBJ_REF_DELTA &&
            trg_entry->in_pack_type != OBJ_OFS_DELTA)
@@ -3192,6 +3196,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
                }
        }
 
+       prepare_packing_data(&to_pack);
+
        if (progress)
                progress_state = start_progress(_("Counting objects"), 0);
        if (!use_internal_rev_list)

diff --git a/object-store.h b/object-store.h
index fef33f345f0a2334f99e09f544d8ea9a8b034e81..71d408786743651b9ee2be9d74696c182752d1b0 100644 (file)
--- a/object-store.h
+++ b/object-store.h
@@ -69,6 +69,7 @@ struct packed_git {
        int index_version;
        time_t mtime;
        int pack_fd;
+       int index;              /* for builtin/pack-objects.c */
        unsigned pack_local:1,
                 pack_keep:1,
                 freshened:1,

diff --git a/pack-objects.c b/pack-objects.c
index 9558d13834e2842d32fa4015f2e3c00538d52dcd..08cfe68b6befe673abe78f99bd3d976449ce0152 100644 (file)
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -2,6 +2,8 @@
 #include "object.h"
 #include "pack.h"
 #include "pack-objects.h"
+#include "packfile.h"
+#include "config.h"
 
 static uint32_t locate_object_entry_hash(struct packing_data *pdata,
                                         const unsigned char *sha1,
@@ -86,6 +88,63 @@ struct object_entry *packlist_find(struct packing_data *pdata,
        return &pdata->objects[pdata->index[i] - 1];
 }
 
+static void prepare_in_pack_by_idx(struct packing_data *pdata)
+{
+       struct packed_git **mapping, *p;
+       int cnt = 0, nr = 1U << OE_IN_PACK_BITS;
+
+       ALLOC_ARRAY(mapping, nr);
+       /*
+        * oe_in_pack() on an all-zero'd object_entry
+        * (i.e. in_pack_idx also zero) should return NULL.
+        */
+       mapping[cnt++] = NULL;
+       for (p = get_packed_git(the_repository); p; p = p->next, cnt++) {
+               if (cnt == nr) {
+                       free(mapping);
+                       return;
+               }
+               p->index = cnt;
+               mapping[cnt] = p;
+       }
+       pdata->in_pack_by_idx = mapping;
+}
+
+/*
+ * A new pack appears after prepare_in_pack_by_idx() has been
+ * run. This is likely a race.
+ *
+ * We could map this new pack to in_pack_by_idx[] array, but then we
+ * have to deal with full array anyway. And since it's hard to test
+ * this fall back code, just stay simple and fall back to using
+ * in_pack[] array.
+ */
+void oe_map_new_pack(struct packing_data *pack,
+                    struct packed_git *p)
+{
+       uint32_t i;
+
+       REALLOC_ARRAY(pack->in_pack, pack->nr_alloc);
+
+       for (i = 0; i < pack->nr_objects; i++)
+               pack->in_pack[i] = oe_in_pack(pack, pack->objects + i);
+
+       FREE_AND_NULL(pack->in_pack_by_idx);
+}
+
+/* assume pdata is already zero'd by caller */
+void prepare_packing_data(struct packing_data *pdata)
+{
+       if (git_env_bool("GIT_TEST_FULL_IN_PACK_ARRAY", 0)) {
+               /*
+                * do not initialize in_pack_by_idx[] to force the
+                * slow path in oe_in_pack()
+                */
+       } else {
+               prepare_in_pack_by_idx(pdata);
+       }
+}
+
 struct object_entry *packlist_alloc(struct packing_data *pdata,
                                    const unsigned char *sha1,
                                    uint32_t index_pos)
@@ -95,6 +154,9 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
        if (pdata->nr_objects >= pdata->nr_alloc) {
                pdata->nr_alloc = (pdata->nr_alloc  + 1024) * 3 / 2;
                REALLOC_ARRAY(pdata->objects, pdata->nr_alloc);
+
+               if (!pdata->in_pack_by_idx)
+                       REALLOC_ARRAY(pdata->in_pack, pdata->nr_alloc);
        }
 
        new_entry = pdata->objects + pdata->nr_objects++;
@@ -107,5 +169,8 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
        else
                pdata->index[index_pos] = pdata->nr_objects;
 
+       if (pdata->in_pack)
+               pdata->in_pack[pdata->nr_objects - 1] = NULL;
+
        return new_entry;
 }

diff --git a/pack-objects.h b/pack-objects.h
index 71ea992c3cd384b34bf3925d70feed1b59c0c8e7..7bedd5af811534ebc5cb10b07fea7e0afb65007c 100644 (file)
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -1,8 +1,11 @@
 #ifndef PACK_OBJECTS_H
 #define PACK_OBJECTS_H
 
+#include "object-store.h"
+
 #define OE_DFS_STATE_BITS      2
 #define OE_DEPTH_BITS          12
+#define OE_IN_PACK_BITS                10
 
 /*
  * State flags for depth-first search used for analyzing delta cycles.
@@ -65,7 +68,7 @@ enum dfs_state {
 struct object_entry {
        struct pack_idx_entry idx;
        unsigned long size;     /* uncompressed size */
-       struct packed_git *in_pack;     /* already in pack */
+       unsigned in_pack_idx:OE_IN_PACK_BITS;   /* already in pack */
        off_t in_pack_offset;
        struct object_entry *delta;     /* delta base object */
        struct object_entry *delta_child; /* deltified objects who bases me */
@@ -100,8 +103,18 @@ struct packing_data {
        uint32_t index_size;
 
        unsigned int *in_pack_pos;
+
+       /*
+        * Only one of these can be non-NULL and they have different
+        * sizes. if in_pack_by_idx is allocated, oe_in_pack() returns
+        * the pack of an object using in_pack_idx field. If not,
+        * in_pack[] array is used the same way as in_pack_pos[]
+        */
+       struct packed_git **in_pack_by_idx;
+       struct packed_git **in_pack;
 };
 
+void prepare_packing_data(struct packing_data *pdata);
 struct object_entry *packlist_alloc(struct packing_data *pdata,
                                    const unsigned char *sha1,
                                    uint32_t index_pos);
@@ -158,4 +171,27 @@ static inline void oe_set_in_pack_pos(const struct packing_data *pack,
        pack->in_pack_pos[e - pack->objects] = pos;
 }
 
+static inline struct packed_git *oe_in_pack(const struct packing_data *pack,
+                                           const struct object_entry *e)
+{
+       if (pack->in_pack_by_idx)
+               return pack->in_pack_by_idx[e->in_pack_idx];
+       else
+               return pack->in_pack[e - pack->objects];
+}
+
+void oe_map_new_pack(struct packing_data *pack,
+                    struct packed_git *p);
+static inline void oe_set_in_pack(struct packing_data *pack,
+                                 struct object_entry *e,
+                                 struct packed_git *p)
+{
+       if (!p->index)
+               oe_map_new_pack(pack, p);
+       if (pack->in_pack_by_idx)
+               e->in_pack_idx = p->index;
+       else
+               pack->in_pack[e - pack->objects] = p;
+}
+
 #endif

diff --git a/t/README b/t/README
index d5e0a3c786d6439550f21bf6c4ad0b387b15a2b4..a06a85bae8afbc07e972aa40c0212da3bca6e521 100644 (file)
--- a/t/README
+++ b/t/README
@@ -304,6 +304,11 @@ environment set.
 GIT_TEST_SPLIT_INDEX=<boolean> forces split-index mode on the whole
 test suite. Accept any boolean values that are accepted by git-config.
 
+GIT_TEST_FULL_IN_PACK_ARRAY=<boolean> exercises the uncommon
+pack-objects code path where there are more than 1024 packs even if
+the actual number of packs in repository is below this limit. Accept
+any boolean values that are accepted by git-config.
+
 Naming Tests
 ------------
 

diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 65ff60f2ee9b4af61f3f2d7d0f889fc4529e2b60..54eff03851dfcb6ba0d4a41a4d0a221edde43729 100755 (executable)
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -457,6 +457,11 @@ test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'pack-objects --threads=N or pack.
        grep -F "no threads support, ignoring pack.threads" err
 '
 
+test_expect_success 'pack-objects in too-many-packs mode' '
+       GIT_TEST_FULL_IN_PACK_ARRAY=1 git repack -ad &&
+       git fsck
+'
+
 #
 # WARNING!
 #