Module IV Memory Organization LFU Page Replacement Algorithm

LFU Page Replacement Algorithm • It involves keeping track of the number of times

LFU Page Replacement • Example • Consider the reference string : 7, 0, 1,

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1,

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Module IV Memory Organization

LFU Page Replacement Algorithm • It involves keeping track of the number of times a page is referenced in memory. • Implementation: – Assign a counter to every block that is loaded into the cache. – Each time a reference is made the counter is incremented – When the cache reaches capacity, system will search for the page with lowest counter and remove it from the cache

LFU Page Replacement • Example • Consider the reference string : 7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 • for a memory with three frames.

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page 7 Frame Hit -1 -1 -1 7(1) -1 -1 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0 2 2(1) 0(1) 1(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0 2 2(1) 0(1) 1(1) 0 0 2(1) 0(2) 1(1) 1

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0 2 2(1) 0(1) 1(1) 0 0 2(1) 0(2) 1(1) 1 3 2(1) 0(2) 3(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0 2 2(1) 0(1) 1(1) 0 0 2(1) 0(2) 1(1) 1 3 2(1) 0(2) 3(1) 0 0 2(1) 0(3) 3(1) 1

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 0 1 7(1) 0(1) 1(1) 0 2 2(1) 0(1) 1(1) 0 0 2(1) 0(2) 1(1) 1 3 2(1) 0(2) 3(1) 0 0 2(1) 0(3) 3(1) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 2(1) 0(2) 1(1) 1 3 2(1) 0(2) 3(1) 0 0 2(1) 0(3) 3(1) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 0 1(1) 0(5) 2(3) 1 2(1) 0(2) 1(1) 1 3 2(1) 0(2) 3(1) 0 0 2(1) 0(3) 3(1) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 0 1(1) 0(5) 2(3) 1 2(1) 0(2) 1(1) 1 1 1(2) 0(5) 2(3) 1 3 2(1) 0(2) 3(1) 0 0 2(1) 0(3) 3(1) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 0 1(1) 0(5) 2(3) 1 2(1) 0(2) 1(1) 1 1 1(2) 0(5) 2(3) 1 3 2(1) 0(2) 3(1) 0 7 7(1) 0(5) 2(3) 0 0 2(1) 0(3) 3(1) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 0 1(1) 0(5) 2(3) 1 2(1) 0(2) 1(1) 1 1 1(2) 0(5) 2(3) 1 3 2(1) 0(2) 3(1) 0 7 7(1) 0(5) 2(3) 0 0 2(1) 0(3) 3(1) 1 0 7(1) 0(6) 2(3) 1 4 4(1) 0(3) 3(1) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0

7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1 Page Frame Hit -1 -1 -1 2 3(2) 0(4) 2(2) 1 0 1 1(1) 0(4) 2(2) 0 1(1) 0 2 1(1) 0(4) 2(3) 1 0(1) 1(1) 0 0 1(1) 0(5) 2(3) 1 2(1) 0(2) 1(1) 1 1 1(2) 0(5) 2(3) 1 3 2(1) 0(2) 3(1) 0 7 7(1) 0(5) 2(3) 0 0 2(1) 0(3) 3(1) 1 0 7(1) 0(6) 2(3) 1 4 4(1) 0(3) 3(1) 0 1 1(1) 0(6) 2(3) 0 2 4(1) 0(3) 2(1) 0 3 3(1) 0(3) 2(1) 0 0 3(1) 0(4) 2(1) 1 3 3(2) 0(4) 2(1) 1 -1 -1 -1 7 7(1) -1 -1 0 0 7(1) 0(1) -1 1 7(1) 0(1) 2 2(1) 0 Hit Ratio = 9/20 No. of Page Faults = 11