Having troubles in updating MTD partitions

hi,
i am trying to change mtd partition sizes, I am successfully able to change size of mtdblock as u can see

cat /proc/partitions
major minor  #blocks  name

  31     0       8192 mtdblock0
  31     1        256 mtdblock1
  31     2       2048 mtdblock2
  31     3       5884 mtdblock3
  31     4          4 mtdblock4
  
 but when i try to use memory relevant tools, it shows me something like 
 # df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root                 5824      5824         0 100% /

5824 was the previous size of mtdblock3

all i have  done is build rootfs with size 5884*1024 and update mtd partition array in kernel, build jffs2 and burn jffs2 in device

there is one more thing, Can any one tell me how i can change eraseblock for a partition, i believe i also having wrong eraseblock for mtdblock3


any help would be appreciative...
thanks