Re: [GSOC] [QUESTION] ref-filter: can %(raw) implement reuse oi.content?

On Wed, Aug 18, 2021 at 6:51 AM ZheNing Hu [off-list ref] wrote:

Christian Couder [off-list ref] 于2021年8月18日周三 上午12:10写道：

quoted

Hi,

On Mon, Aug 16, 2021 at 4:00 PM ZheNing Hu [off-list ref] wrote:

quoted

Hi,

In the implementation of %(raw) atom
(bd0708c7 ref-filter: add %(raw) atom), we use xmemdupz()
to copy the content of the object. But if we can reuse the content
of the object?

Since git cat-file --batch needs to use ref-filter
as the backend, if the object buffer can be reused correctly here,
we can save a lot of copies and improve its performance by about 6%.

Yeah, that would be great.

quoted

Tracing back to the source, the object buffer is allocated from
oid_object_info_extended(), but in parse_object_buffer() we may lose
the ownership of the buffer (maybe the buffer is eaten), but I browsed the
source code of for-each-ref.c or cat-file.c, and I don’t seem to find that the
buffers which have been eaten are released by the program.

So can we reuse it?

This is what I want to do:

diff --git a/ref-filter.c b/ref-filter.c
index 93ce2a6ef2..1f6c1daabd 100644
--- a/ref-filter.c
+++ b/ref-filter.c

@@ -1443,7 +1443,7 @@ static void grab_sub_body_contents(struct

atom_value *val, int deref, struct exp
                        unsigned long buf_size = data->size;

                        if (atom->u.raw_data.option == RAW_BARE) {
-                               v->s = xmemdupz(buf, buf_size);
+                               v->s = buf;

It seems to me that this could work only if 'buf' isn't freed. Have
you checked that? Did we leak 'buf' before this patch? Otherwise when
are we freeing it?

This is how I use gdb find out if this buffer have been freed:

I was asking about 'buf' before the patch.

Before the patch, we were doing:

v->s = xmemdupz(buf, buf_size);

which means that in v->s there is a copy of 'buf', not 'buf' itself.
So I was wondering if 'buf' was freed then, not the copy in in v->s.