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Satori: Enlightened page sharing

Satori: Enlightened page sharing. Grzegorz Milos et al., USENIX 09. presenter : Dongwoo Kang rediori@dankook.ac.kr. Contents. Motivation Satori Implementation Evaluation Conclusion. Motivation. Difficult to Increase the Memory Size. Increase memory capacity

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Satori: Enlightened page sharing

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  1. Satori: Enlightened page sharing Grzegorz Milos et al., USENIX 09 presenter : Dongwoo Kang rediori@dankook.ac.kr

  2. Contents • Motivation • Satori • Implementation • Evaluation • Conclusion

  3. Motivation

  4. Difficult to Increase the Memory Size • Increase memory capacity • Need Extra slots on the mother board • Need higher-capacity modules • Consume significant power • High density memory is expensive source : http://www.legitreviews.com/article/1882/4/

  5. Page Sharing Cycle Duplicates Page Copy Shared Page Private Page Write Attempt Reclaimed Duplicates

  6. Motivation -1 • Previous work • Detect sharing page by periodically scanning the memory of all guest VMs • Scanning at a higher rate • More sharing opportunities, • Use more CPU • Scan, Compare fingerprints • Overcommit • VMM must be able to page guest memory to and from disk

  7. Motivation -2 • Life time of many shareable pages is short • KBUILD-256 • Vanilla Linux 2.6.24 kernel build with 256MB of physical memory • KBUILD-512 • Vanilla Linux 2.6.24 kernel build with 512MB of physical memory

  8. Satori The state of sudden indescribable intuitive enlightenment from Wiki VMs

  9. Satori

  10. What is the goal of Satori? • Two Goals • Detect short-lived sharing • Detect sharing cheaply • Two Technique • Sharing-aware block devices • Repayment FIFO

  11. How are duplicates detected? • Many sharing opportunities are short-lived • 63.8% ~ 93.0% of shareable pages between VMs are part of the page cache • J.F.Kloster et al., “Determining the use of Interdomain Shareable Pages using Kernel Introspection”, 2007 • Use Sharing-aware block devices • low-overhead mechanism for detecting duplicates pages

  12. Sharing-aware block devices • It was implemented in tapdisk • Content-based sharing • Copy-on-write disk sharing • Identical OSes use identical data • binaries( kernel + programs ) • libraries • configuration files • some data files source : presentation of satori

  13. How are memory savings distributed? • Difference Engine • Satori New VM Page Shared Page Reclaimed Duplicates VM VM VM Page Reclaimed Duplicates Shared Page

  14. Sharing entitlement • n is duplicates of the same page • it will reclaim n – 1 redundant copies • Contributing VM • (n-1)/n • Sharing entitlement p : each page n(p) : sharing rank of page M(i) : For VM i, which uses the set of pages s(i) : Sharing entitlement

  15. Example of Sharing entitlements sharing entitlements pseudo-physical pages machine pages VM 1 VM 2

  16. Example of Sharing entitlements sharing entitlements 1/2 1/2 pseudo-physical pages machine pages VM 1 VM 2

  17. Example of Sharing entitlements sharing entitlements 1/2 1/2 pseudo-physical pages New Page machine pages VM 1 VM 2

  18. Example of Sharing entitlements sharing entitlements 1/2 1/2 pseudo-physical pages Shareable machine pages VM 1 VM 2

  19. Example of Sharing entitlements sharing entitlements 2/3 4/3 2/3 2/3 pseudo-physical pages 2/3 machine pages VM 1 VM 2

  20. What if sharing is broken? • Need some more memory • Typically use Host Paging • Modify the OS to nominate “Volatile Pages” • Clean buffer cache pages Duplicates Page Copy Shared Page Private Page Write Attempt Reclaimed Duplicates repay use Repayment FIFO

  21. Satori • Detect sharing quickly and cheaply • HVM scans guest memory and compares fingerprints • Monitors virtual I/O devices • Distribute memory saving fairly • HVM manages common pool of surplus memory • VMs receive sharing entitlements in proportion to # pages shared • Reclaim memory efficiently • HVM implements secondary memory paging algorithm • Memory managed exclusively by the VMs sharing exposed to the VMs

  22. Implementation

  23. Implementation • Xen Hypervisor • 5351 LOC • Low-level sharing support • sharing entitlement computation • fault handling • Dom 0 • 3894 LOC • sharing-aware block devices • management tools • Dom U • 2306 LOC • Repayment FIFO • based IBM CMM

  24. Evaluation

  25. Environments • Dell PowerEdge 1425 server • 2 x 2.8GHz Xeon CPUs • 2.5GB memory • 80GB Seagate SATA disk • VMs ran Ubuntu Linux 8.04 • Benchmark • KBUILD-256,512 • HTTPERF(512MB) • RUBiS(512MB)

  26. Shareable Opportunities • Achieves 94% Opp HTTPERF • Achives 91% OppRUBiS • Achives 50% Opp KBUILD-512

  27. Performance

  28. Conclusion

  29. Conclusion • Satori no need memory scan • Detection cheap and effective • Satori is effective • High Coverage( HTTPERF, RUBiS)

  30. Q & A

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