clarification about Algorithm of page replacement LRU with reference bits Studying LRU approximation Algorithms I think to have not understand how it works, for example: 

consider a process with 3 logical pages and 2 frames allocated , an approximation of the
Algorithm Last Recently Used based of reference bits where every four references there is
a shift and where are considered just the first 2 bits, and the follow reference string:



  1 2 1 1 1 1 0 1 0 0 


I'd solve it in this way:


  1 2 1 1 (m1) 1 1 (m2) 0 1 0 0  


(m1)

4 references so I'd pass from 

 frame                     frame
 -----+---+---     to       -----+---+---
    1 | 1 | 0                  1 | 0 | 1 
    2 | 1 | 0                  2 | 0 | 1 


(m2)

page fault so I'd pass from 

 frame                     frame
 -----+---+---     to       -----+---+---
    1 | 1 | 1                  1 | 0 | 0 
    2 | 0 | 1                  0 | 0 | 0 


So the questions are:


Is my doing correct?
At m2 there is a page fault, is there a "reset" and all bits puts at 0?
the shift frequency (4 in the example) restart counting every page fault?
Is my doing correct?


If I don't misunderstand your notation, when you manipulate the frame for first time (filling it with page 1, then page 2) and then page 1 is called again, you shouldn't send to disk page 2, there is no need because page 1 it is already in frame.