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Re: [PATCH] fetch-pack.c: use oidset to check existence of loose object




2018-03-09 2:19 GMT+09:00 René Scharfe <l.s.r@xxxxxx>:
> Am 08.03.2018 um 13:06 schrieb Takuto Ikuta:
>> +static int add_loose_objects_to_set(const struct object_id *oid,
>> +                                 const char *path,
>> +                                 void *data)
>> +{
>> +     struct oidset* set = (struct oidset*)(data);
>
> This cast is not needed (unlike in C++).  And the asterisk should be stuck
> to the variable, not the type (see Documentation/CodingGuidelines).
>
>> +     oidset_insert(set, oid);
>
> In fact, you could just put "data" in here instead of "set" (without a
> cast), with no loss in readability or safety.
>

Thank you for review, changed to use data directly in v2.

>> +     return 0;
>> +}
>> +
>>   static int everything_local(struct fetch_pack_args *args,
>>                           struct ref **refs,
>>                           struct ref **sought, int nr_sought)
>> @@ -719,16 +728,21 @@ static int everything_local(struct fetch_pack_args *args,
>>       int retval;
>>       int old_save_commit_buffer = save_commit_buffer;
>>       timestamp_t cutoff = 0;
>> +     struct oidset loose_oid_set = OIDSET_INIT;
>> +
>> +     for_each_loose_object(add_loose_objects_to_set, &loose_oid_set, 0);
>>
>>       save_commit_buffer = 0;
>>
>>       for (ref = *refs; ref; ref = ref->next) {
>>               struct object *o;
>> +             unsigned int flag = OBJECT_INFO_QUICK;
>>
>> -             if (!has_object_file_with_flags(&ref->old_oid,
>> -                                             OBJECT_INFO_QUICK))
>> -                     continue;
>> +             if (!oidset_contains(&loose_oid_set, &ref->old_oid))
>> +                     flag |= OBJECT_INFO_SKIP_LOOSE;
>>
>> +             if (!has_object_file_with_flags(&ref->old_oid, flag))
>> +                     continue;
>>               o = parse_object(&ref->old_oid);
>>               if (!o)
>>                       continue;
>> @@ -744,6 +758,8 @@ static int everything_local(struct fetch_pack_args *args,
>>               }
>>       }
>>
>> +     oidset_clear(&loose_oid_set);
>> +
>
> This part looks fine to me.  (Except perhaps call the variable "flags"
> because you sometimes have two?)
>

Changed flag names.

> Why not include packed objects as well?  Probably because packs have
> indexes which can queried quickly to determine object existence, and
> because there are only few loose objects in typical repositories,
> right?
>

Correct. In my target repository, chromium, fetch-pack's slowness
comes from many lstat
to non-existing loose objects for remote refs. I focus on to remove such lstat.

> A similar cache was introduced by cc817ca3ef (sha1_name: cache
> readdir(3) results in find_short_object_filename()) to speed up
> finding unambiguous shorts object hashes.  I wonder if it could be
> used here as well, but I don't see an easy way.
>
>>       if (!args->no_dependents) {
>>               if (!args->deepen) {
>>                       for_each_ref(mark_complete_oid, NULL);
>> diff --git a/sha1_file.c b/sha1_file.c
>> index 1b94f39c4..c903cbcec 100644
>> --- a/sha1_file.c
>> +++ b/sha1_file.c
>> @@ -1262,6 +1262,9 @@ int sha1_object_info_extended(const unsigned char *sha1, struct object_info *oi,
>>               if (find_pack_entry(real, &e))
>>                       break;
>>
>> +             if (flags & OBJECT_INFO_SKIP_LOOSE)
>> +                     return -1;
>> +
>>               /* Most likely it's a loose object. */
>>               if (!sha1_loose_object_info(real, oi, flags))
>>                       return 0;
>>
>
> This early return doesn't just skip checking loose objects.  It
> also skips reloading packs and fetching missing objects for
> partial clones.  That may not be a problem for fetch-pack, but
> it means the flag has a misleading name.  Do you get the same
> performance improvement if you make it only skip that
> sha1_loose_object_info() call?
>

I changed the flag name following Junio's suggestion. If we skip
sha1_loose_object_info call,
reprepare_packed_git(...) runs for every non-existing refs and git
fetch becomes slower.

Takuto