Re: Move PinBuffer and UnpinBuffer to atomics

I was looking into this patch, overall patch looks good to me, I want to
know what is the current state of this patch, is there some pending task in
this patch ?

Patch was not applying on head so i have re based it and re based version is
attached in the mail.

I have done some performance testing also..

Summary:
---------------
1. In my test for readonly workload i have observed some improvement for scale factor 1000.
2. I have also observed some regression with scale factor 300 (I can't say
it's actual regression  or just run to run variance), I thought that may be problem with lower scale factor so tested with scale factor 100 but with s.f. 100 looks fine.

Machine Detail:
cpu   : POWER8

cores: 24 (192 with HT)

Non Default Parameter:
------------------------
Shared Buffer= 30GB
max_wal_size= 10GB
max_connections=500

Test1:
pgbench -i -s 1000 postgres
pgbench -c$ -j$ -Mprepared -S postgres

Client             Base                      Pached

1                       19753                   19493
32                   344059                 336773
64                   495708                 540425
128                 564358                 685212
256                 466562                 639059

Test2:
pgbench -i -s 300 postgres
pgbench -c$ -j$ -Mprepared -S postgres

Client             Base                      Pached

1                      20555                    19404
32                  375919                  332670
64                  509067                  440680
128                431346                  415121
256                380926                  379176       

Test3:
pgbench -i -s 100 postgres
pgbench -c$ -j$ -Mprepared -S postgres

Client             Base                      Pached

1                      20555                    19404
32                  375919                  332670
64                  509067                  440680
128                431346                  415121
256                380926                  379176