a question about page cache and buffer cache in kernel 2.4.18

["Bao zhao" <paozhaokeats@xxxxxxxxxxx>]

    when a block device such as /dev/hda1 was read  as device file 
open("/dev/hda1",...) ,page cache was set up,the buffer cache's physical 
block number  for the page is adjacent  .  but when a file name a.txt  in 
/dev/hda1 was read  . open("/../a.txt",...),page cache was set up too,but 
the buffer cache needn't be adjacent.
so, there may be two copy in page cache for the same physical block,how can 
they be consitent?
when read a regular file,block_read_full_page was called ,it never find if 
the buffer cache of the page has already in the anothe page .
     I am  confused by this,anyone helps me out? Thanks!

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