do not discard revindex when re-preparing packfiles

When an object lookup fails, we re-read the objects/pack
directory to pick up any new packfiles that may have been
created since our last read. We also discard any pack
revindex structs we've allocated.

The discarding is a problem for the pack-bitmap code, which keeps
a pointer to the revindex for the bitmapped pack. After the
discard, the pointer is invalid, and we may read free()d
memory.

Other revindex users do not keep a bare pointer to the
revindex; instead, they always access it through
revindex_for_pack(), which lazily builds the revindex. So
one solution is to teach the pack-bitmap code a similar
trick. It would be slightly less efficient, but probably not
all that noticeable.

However, it turns out this discarding is not actually
necessary. When we call reprepare_packed_git, we do not
throw away our old pack list. We keep the existing entries,
and only add in new ones. So there is no safety problem; we
will still have the pack struct that matches each revindex.
The packfile itself may go away, of course, but we are
already prepared to handle that, and it may happen outside
of reprepare_packed_git anyway.

Throwing away the revindex may save some RAM if the pack
never gets reused (about 12 bytes per object). But it also
wastes some CPU time (to regenerate the index) if the pack
does get reused. It's hard to say which is more valuable,
but in either case, it happens very rarely (only when we
race with a simultaneous repack). Just leaving the revindex
in place is simple and safe both for current and future
code.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/pack-revindex.c b/pack-revindex.c
index 0bb13b1ba62ed4bc091c9a2a22266839dba05d7d..5bd7c619803c8457a8c1a1a69a11758d34b49eac 100644 (file)
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -245,14 +245,3 @@ struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
 
        return pridx->revindex + pos;
 }
-
-void discard_revindex(void)
-{
-       if (pack_revindex_hashsz) {
-               int i;
-               for (i = 0; i < pack_revindex_hashsz; i++)
-                       free(pack_revindex[i].revindex);
-               free(pack_revindex);
-               pack_revindex_hashsz = 0;
-       }
-}

diff --git a/pack-revindex.h b/pack-revindex.h
index 866ca9c57137b0c4143157bc97f4aa21aac87887..d737f989659da7f58d7df153de9a2ac30b162108 100644 (file)
--- a/pack-revindex.h
+++ b/pack-revindex.h
@@ -15,6 +15,5 @@ struct pack_revindex *revindex_for_pack(struct packed_git *p);
 int find_revindex_position(struct pack_revindex *pridx, off_t ofs);
 
 struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs);
-void discard_revindex(void);
 
 #endif

diff --git a/sha1_file.c b/sha1_file.c
index 129496250c3673c1f62a5da5db728703501ddf0f..36d55c05f782e717c8d3a730878050fee390fe5a 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1279,7 +1279,6 @@ void prepare_packed_git(void)
 
 void reprepare_packed_git(void)
 {
-       discard_revindex();
        prepare_packed_git_run_once = 0;
        prepare_packed_git();
 }