[HAIFUX LECTURE] Efficient Virtual Memory: Hash, Don't Walk -- Idan Yaniv

[Eli Billauer]

On Monday, June 23rd at 18:30, Haifux will gather to hear a talk by Idan Yaniv:

    Efficient Virtual Memory: Hash, Don't Walk

Abstract

Radix page tables as implemented in the x86-64 micro-architecture incur 
a penalty of four memory references on each TLB miss. The problem 
aggravates in virtualized environments with nested page tables where 
every page walk requires 24 memory references. The virtual memory 
overhead on guest performance can approach 90% in servers or scientific 
applications.

Trying to mitigate the cost of TLB misses hardware vendors have added 
MMU caches that store partial translations. Current MMU caches exploit 
the reuse of page table entries to accelerate native address 
translation. Extending those caches to support 2D page walks in 
virtualized systems will make the hardware more complicated and power 
consuming.

We propose using hashed page tables for both native and virtualized 
systems. A recent study have concluded that hashed page tables increase 
the number of DRAM accesses per walk by over 400%. However we show that 
properly designed hashed page tables are even superior to the radix page 
tables augmented with MMU caches. Our results indicate that hash-based 
page tables are particularly effective for virtualized systems and 
nested virtualization.


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We meet in Taub building, room 6. For instructions see:
http://www.haifux.org/where.html

Attendance is free, and you are all invited!

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Future lectures:

There are no scheduled lectures.


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