CSE 120 Lecture Notes - Lecture 12: Working Set, Readwrite, Busy Waiting

50 views3 pages
Published on 27 Feb 2018
School
Course
Resident Set Manageement
-”resident set” - process’ pages in physical memory
-Need: how big the set is, and WHICH pages
Local: limit frame selection to requesting process
-I.e. If a process needs to bring in a page, it HAS to kick out one of its existing pages
-isolates effects of behavior on processes
Global approach: select ANY frame (from ANY process)
-may get more “efficiency”
-lose isolation - processes can negatively affect another
Multiprogramming Level - the # of processes in physical memory
(i.e. non-empty resident sets)
-Processor utilization - how “busy” a process is doing useful work (NOT busy waiting, or time it
takes to execute a context switch)
Goal: as MP level increases, so does Process utilization
Note: not all processes are “compute-bound” - i.e. ONLY use the CPU
-thrashing: we don’t want a whole bunch of processes ASKING for resources, and then they
are all “busy-waiting” to get them
-that’s why you see the curve “crashing down” at the end
-how do we deal with this? Concept of the working set
-we want the resident set to be part of the working set
Denning’s Working Set Model
Working Set: pages referenced during the window of Δ of time units
| ← Working Set → |
t - Δ t
-Varies based on # of pages referenced during the window
-if there is locality, the WS represents pages that were recently used
-if WS doesn’t “fit”, swap a process out!
-instead of “partially” allowing a process’s pages in the window, just remove the process
entirely
=> swap - if you can bring in a process’ WS in PM, then do it. If you can’t, throw it out!
Vs paging - bringing pages in “one at a time”
-WS is a local replacement policy - process’ page fault behavior does NOT affect others
Problem: difficult to implement!
- Have to “categorize” ALL pages as IN the WS or OUT
- Must “timestamp” pages in WS
- Assumes an “intelligent” Δ is picked (we could’ve chose a Δ too big that we have pages
that we really do NOT need, or a Δ too small we are missing crucial pages!)
- Have to experiment on Δ!
-in contrast to Clock - easy to implement, but a global policy
Summary
Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
Monthly
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.