Re: [PATCH] bisect: save heap memory. allocate only the required amount

Arjun Sreedharan [off-list ref] writes:

Find and allocate the required amount instead of allocating extra
100 bytes

Signed-off-by: Arjun Sreedharan <redacted>
---

Interesting.  How much memory do we typically waste (in other words,
how big did "cnt" grew in your repository where you noticed this)?

Decl-after-stmt.

You do not have to run a separate strlen() for this.  The return
value from sprintf() should tell you how much you need to allocate,
I think.

+		struct name_decoration *r = xmalloc(sizeof(*r) + name_len);
 		struct object *obj = &(array[i].commit->object);
 
-		sprintf(r->name, "dist=%d", array[i].distance);
+		memcpy(r->name, name, name_len + 1);
 		r->next = add_decoration(&name_decoration, obj, r);
 		p->item = array[i].commit;
 		p = p->next;

On 26 August 2014 02:44, Junio C Hamano [off-list ref] wrote:

Arjun Sreedharan [off-list ref] writes:

quoted

Find and allocate the required amount instead of allocating extra
100 bytes

Signed-off-by: Arjun Sreedharan <redacted>
---

Interesting.  How much memory do we typically waste (in other words,
how big did "cnt" grew in your repository where you noticed this)?

I did not try to make an observation of that. I was thinking we're
anyway better off
not using a magic number to allot memory on the heap for each item in
the commit list.

quoted

 bisect.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/bisect.c b/bisect.c
index d6e851d..c96aab0 100644
--- a/bisect.c
+++ b/bisect.c

@@ -215,10 +215,13 @@ static struct commit_list *best_bisection_sorted(struct commit_list *list, int n
      }
      qsort(array, cnt, sizeof(*array), compare_commit_dist);
      for (p = list, i = 0; i < cnt; i++) {
-             struct name_decoration *r = xmalloc(sizeof(*r) + 100);
+             char name[100];
+             sprintf(name, "dist=%d", array[i].distance);
+             int name_len = strlen(name);

Decl-after-stmt.

You do not have to run a separate strlen() for this.  The return
value from sprintf() should tell you how much you need to allocate,
I think.

Yes. yes.

quoted

+             struct name_decoration *r = xmalloc(sizeof(*r) + name_len);
              struct object *obj = &(array[i].commit->object);

-             sprintf(r->name, "dist=%d", array[i].distance);
+             memcpy(r->name, name, name_len + 1);
              r->next = add_decoration(&name_decoration, obj, r);
              p->item = array[i].commit;
              p = p->next;