Re: [PATCH 1/2] packfile: close and free packs upon releasing an object store

[Jeff King]

On Wed, May 09, 2018 at 05:12:10PM -0700, Stefan Beller wrote:

> In d0b59866223 (object-store: close all packs upon clearing the object
> store, 2018-03-23), we made sure to close all packfiles on releasing
> an object store, but we also have to free the memory of the closed packs.

I know we've assumed in a few places that a "struct packed_git" will
never go away. The one that comes to mind is the mru list.

It looks like we'll be OK here:

> diff --git a/object.c b/object.c
> index 66cffaf6e51..3e64a4a26dd 100644
> --- a/object.c
> +++ b/object.c
> @@ -485,6 +485,6 @@ void raw_object_store_clear(struct raw_object_store *o)
>   o->alt_odb_tail = NULL;
>  
>   INIT_LIST_HEAD(>packed_git_mru);
> - close_all_packs(o);
> + close_and_free_packs(o);
>   o->packed_git = NULL;
>  }

because we clear the list above. But it would be dangerous for anybody
else to call close_and_free_packs(). Should that INIT_LIST_HEAD get
moved down into that function?

Probably the same applies to setting NULL here; you're left with a
dangling pointer if you just call close_and_free_packs(). Should
that helper maybe just be a static function in object.c?


Just brainstorming other places where the immutability of "struct
packed_git" might be important:

  - pack-objects keeps a pointer from each object_entry to its
containing packed_git. That's probably OK, as you wouldn't expect to
be able to close the object store in the middle of that operation.

  - the reachability bitmap code holds a pointer to the pack that has a
bitmap. Probably that whole "struct bitmap_index" needs to be part
of the object_store (arguably it should all just be _inside_ the
packed_git, but the current implementation avoids complexity by just
having a single bitmap-per-repo).

-Peff

[PATCH 1/2] packfile: close and free packs upon releasing an object store

[Stefan Beller]

In d0b59866223 (object-store: close all packs upon clearing the object
store, 2018-03-23), we made sure to close all packfiles on releasing
an object store, but we also have to free the memory of the closed packs.

Signed-off-by: Stefan Beller 
---
 object.c   |  2 +-
 packfile.c | 11 +++
 packfile.h |  1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/object.c b/object.c
index 66cffaf6e51..3e64a4a26dd 100644
--- a/object.c
+++ b/object.c
@@ -485,6 +485,6 @@ void raw_object_store_clear(struct raw_object_store *o)
o->alt_odb_tail = NULL;
 
INIT_LIST_HEAD(>packed_git_mru);
-   close_all_packs(o);
+   close_and_free_packs(o);
o->packed_git = NULL;
 }
diff --git a/packfile.c b/packfile.c
index 6c3ddc3c31d..ba4baa55531 100644
--- a/packfile.c
+++ b/packfile.c
@@ -322,6 +322,17 @@ void close_all_packs(struct raw_object_store *o)
close_pack(p);
 }
 
+void close_and_free_packs(struct raw_object_store *o)
+{
+   close_all_packs(o);
+
+   while (o->packed_git) {
+   struct packed_git *p = o->packed_git;
+   o->packed_git = p->next;
+   free(p);
+   }
+}
+
 /*
  * The LRU pack is the one with the oldest MRU window, preferring packs
  * with no used windows, or the oldest mtime if it has no windows allocated.
diff --git a/packfile.h b/packfile.h
index 9c2f8859945..cdab0557979 100644
--- a/packfile.h
+++ b/packfile.h
@@ -67,6 +67,7 @@ extern unsigned char *use_pack(struct packed_git *, struct 
pack_window **, off_t
 extern void close_pack_windows(struct packed_git *);
 extern void close_pack(struct packed_git *);
 extern void close_all_packs(struct raw_object_store *o);
+extern void close_and_free_packs(struct raw_object_store *o);
 extern void unuse_pack(struct pack_window **);
 extern void clear_delta_base_cache(void);
 extern struct packed_git *add_packed_git(const char *path, size_t path_len, 
int local);
-- 
2.17.0.255.g8bfb7c0704