I sent 2 versions of this patchset. Here is the second one
with discussed approach:
https://lists.tarantool.org/pipermail/tarantool-patches/2020-February/014191.html
And tarantool/small patch:
https://lists.tarantool.org/pipermail/tarantool-patches/2020-February/014190.html 
>Суббота, 15 февраля 2020, 0:00 +03:00 от Konstantin Osipov <kostja.osipov@gmail.com>:
> 
>* Ilya Kosarev < i.kosarev@tarantool.org > [20/02/14 22:41]:
>> Changes in v2:
>> Approach changed completely: now we are not trying to allocate
>> service tuples in some safe way, but increasing memtx quota so
>> that space:truncate() and space:delete() won't fail on allocation.
>
>
>>
>> Changes in v3:
>> Now we are not increasing memtx quota. Instead we just set a flag to
>> allow quota overuse for space:truncate() and space:delete().
>>
>> Changes in v4:
>> improved quota on/off flag style
>> took into account fail cases for box_upsert in space_truncate
>> now we are switching the quota off for deletion only in case there is
>> OutOfMemory error in diag
>> removed extra checks
>> added tests
>
>Is it intentional that first you discuss the
>recommendation I make on the mailing list, and then silently
>disregard it?
>
>--
>Konstantin Osipov, Moscow, Russia 
 
 
--
Ilya Kosarev