RE: [Patch] Optimize dropping of relation buffers using dlist

Hi Amit,

In last
mail(https://www.postgresql.org/message-id/66851e198f6b41eda59e6257182564b6%40G08CNEXMBPEKD05.g08.fujitsu.local),
I've sent you the performance test results(run only 1 time) on single table. Here is my the retested results(average by
15times) which I think is more accurate.
 

In terms of 20G and 100G, the optimization on 100G is linear, but 20G is nonlinear(also include test results on shared
buffersof 50G/60G), so it's a little difficult to decide the threshold from the two for me. 
 
If just consider 100G, I think NBuffers/32 is the optimized max relation size. But I don't know how to judge for 20G.
Ifyou have any suggestion, kindly let me know.
 

#%reg            128M    1G    20G    100G
---------------------------------------------------------------
%reg(NBuffers/512)     0%    -1%    -5%    -26%
%reg(NBuffers/256)     0%     0%     5%    -20%
%reg(NBuffers/128)    -1%    -1%    -10%    -16%
%reg(NBuffers/64)    -1%     0%     0%     -8%    
%reg(NBuffers/32)     0%     0%    -2%    -4%
%reg(NBuffers/16)     0%     0%    -6%     4%
%reg(NBuffers/8)     1%     0%     2%    -2%
%reg(NBuffers/4)     0%     0%     2%     2%

Optimization details(unit: second):
patched     (sec)                    
shared_buffers    NBuffers/512    NBuffers/256    NBuffers/128    NBuffers/64    NBuffers/32    NBuffers/16
NBuffers/8   NBuffers/4
 

----------------------------------------------------------------------------------------------------------------------------------------------------------
128M        0.107        0.107        0.107        0.107        0.107        0.107        0.108        0.208
1G        0.107        0.108        0.107         0.108         0.208         0.208         0.308         0.409 
20G        0.199         0.299         0.317         0.408         0.591         0.900         1.561         2.866 
100G        0.318         0.381         0.645         0.992         1.913         3.640         6.615         13.389

master(HEAD) (sec)                    
shared_buffers    NBuffers/512    NBuffers/256    NBuffers/128    NBuffers/64    NBuffers/32    NBuffers/16
NBuffers/8   NBuffers/4
 

----------------------------------------------------------------------------------------------------------------------------------------------------------
128M        0.107        0.107        0.108        0.108        0.107        0.107        0.107        0.208
1G        0.108         0.108         0.108         0.108         0.208         0.207         0.308         0.409 
20G        0.208         0.283         0.350         0.408         0.601         0.955         1.529         2.806 
100G        0.400         0.459         0.751         1.068         1.984         3.506         6.735         13.101

Regards
Tang