Add umf_ba_linear_pool_contains_pointer

[ldorau]

Add umf_ba_linear_pool_contains_pointer().
It returns:

• 0 if ptr does not belong to the pool or
• size (> 0) of the memory region from ptr to the end of the pool if ptr belongs to the pool.

It will be useful to implement realloc() in the proxy library.

Requires:

• Fix: make it possible to allocate more than initial pool size #221

[ldorau]

BTW: the code was copied from #218 by @igchor

[igchor]

Looks good. But can you explain why this will be needed for proxy pool? I still don't understand why we can't just detect recursion in malloc/free (globally, not per pointer) and then call appropriate function (base_alloc or umf*)

[ldorau]

Looks good. But can you explain why this will be needed for proxy pool? I still don't understand why we can't just detect recursion in malloc/free (globally, not per pointer) and then call appropriate function (base_alloc or umf*)

If free() is called from "outside world" (not from inside of malloc()), it does not know if the pointer it gets comes from the base allocator or from the pool manager, so it has to check that.

[igchor]

Looks good. But can you explain why this will be needed for proxy pool? I still don't understand why we can't just detect recursion in malloc/free (globally, not per pointer) and then call appropriate function (base_alloc or umf*)

If free() is called from "outside world" (not from inside of malloc()), it does not know if the pointer it gets comes from the base allocator or from the pool manager, so it has to check that.

How can a pointer from the 'outside world' come from the base allocator? If a user calls 'free', the pointer has to come from a 'malloc' which means it has to be part of the umf pool, right?

[bratpiorka]

this code looks ok but please don't merge unless we need it

[ldorau]

Looks good. But can you explain why this will be needed for proxy pool? I still don't understand why we can't just detect recursion in malloc/free (globally, not per pointer) and then call appropriate function (base_alloc or umf*)

If free() is called from "outside world" (not from inside of malloc()), it does not know if the pointer it gets comes from the base allocator or from the pool manager, so it has to check that.

How can a pointer from the 'outside world' come from the base allocator? If a user calls 'free', the pointer has to come from a 'malloc' which means it has to be part of the umf pool, right?

@igchor Hundreds of pointers can come from the base allocator:

1. An app starts with LD_PRELOAD=proxy_lib
2. libc calls malloc() ... (they come from the base allocator):

>>> malloc(72704)
>>> realloc(0x0, 416)
>>> malloc(20)
>>> malloc(24)

3. The constructor of proxy_lib starts ...
4. The constructor of proxy_lib calls umfMemoryProviderCreate(umfOsMemoryProviderOps()) and hwloc calls hundreds of malloc()s (they come from the base allocator):

>>> malloc(896)
>>> malloc(32)
>>> malloc(32816)
>>> malloc(100)
>>> malloc(44)
...

5. The constructor of proxy_lib calls umfPoolCreate(umfJemallocPoolOps())
6. The UMF pool is created. All allocations starting from this point come from the UMF pool.
   ...
7. An app calls free(ptr) - does the ptr come from the base allocator or from the UMF pool ???

[ldorau]

Closing for now - it will be reopened as a part of the pull request with the proxy library ...