Double shared memory allocation for SLRU LWLocks

Hi, all!

It seems to me that we're allocating shared memory for SLRU lwlocks twice,
unless I'm missing something.

SimpleLruShmemSize() calculates total SLRU shared memory size including
lwlocks size.

SimpleLruInit() starts with line

shared = (SlruShared) ShmemInitStruct(name,
SimpleLruShmemSize(nslots, nlsns),
&found);

which allocates SLRU shared memory (LWLocks size is included because
SimpleLruShmemSize() is used for size computation).

Following line allocates shared memory for LWLocks again:
shared->buffer_locks = (LWLockPadded *) ShmemAlloc(sizeof(LWLockPadded) *
nslots);

Attached patch fixes that by removing extra ShmemAlloc for SLRU.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company