dd if=/dev/urandom of=file1 bs=4M count=100procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ ---timestamp--- r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st 1  0  81292 167664 201032 1508732    0    0     0    32 2454 2348  1 26 73  0  0   2016-08-03 15:48:20 EDT 3  0  81292 146876 201044 1529212    0    0     0    36 2475 2354  1 26 74  0  0   2016-08-03 15:48:22 EDT 1  1  86708 118788  97164 1666232    0 2710    60 455344 3758 2568  0 35 61  3  0  2016-08-03 15:48:24 EDT 1  1  87100  46968  78276 1785072    0  196 177784 344372 10116 19394  0 18 57 25  0   2016-08-03 15:48:26 EDT 1  1  87100  46980  14140 1858056    0    0 180438 335958 8920 13661  0 16 52 32  0    2016-08-03 15:48:28 EDT 1  1  87100  47056   1800 1873748    0    0 172372 344166 11690 32146  0 17 59 24  0   2016-08-03 15:48:30 EDT 1  2  87100  47148   1144 1875992    0    0 173494 409690 6167 5277  0 17 49 34  0 2016-08-03 15:48:32 EDT 0  2  87100  47124   1312 1873632    0    0 151148 475280 7945 16188  0 18 54 28  0    2016-08-03 15:48:34 EDT 0  2  87100  47144   1248 1877000    0    0 149456 409720 6872 4996  0 17 51 32  0 2016-08-03 15:48:36 EDT 1  1  87108 191464   1476 1731200    0    4 104284 552572 10381 20498  6 21 48 24  0   2016-08-03 15:48:38 EDT 1  1  87116  63164   1300 1860596    0    4  4790 819374 9791 44709  0 28 60 11  0 2016-08-03 15:48:40 EDT 1  0  87116  83424   1340 1834620    0    0  3294 803514 6719 21763  1 29 57 13  0 2016-08-03 15:48:42 EDT 1  1  87116  52400   1436 1865280    0    0    36 780498 5422 2537  0 28 71  1  0  2016-08-03 15:48:44 EDT 1  0  87116  56136   1472 1865336    0    0     2 784830 6392 27997  0 28 69  2  0 2016-08-03 15:48:46 EDTWhy I am observing a deep drop in the buff and Swpd values? while my cache size grows?  observing this behaviour only when I try to use 4M block size. When using 1M block size I simply see the buff content grows. is there a logical explantion what is happening?
dd command 4M block size - buff cache
linux;caching;dd