virtual memory

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RANGE TRANSLATIONS FOR FAST
VIRTUAL MEMORY
Rahul &Sunil
Mtech-CSE Sem-I
ASE Bangalore
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Introduction to Virtual memory and TLB
• virtual memory is a memory management technique that is implemented using
both hardware and software. It maps memory addresses used by a program,
called virtual addresses into physical addresses in computer memory.
• Each process has a large private virtual address space which are typically 4K
bytes in size.
• Memory Manager divides the virtual address space into equal sized pieces
called pages
• Memory Manager divides the physical address space into equal sized pieces
called frames
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3. MMU with TLB
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• TLB hit.
• TLB miss.
• Logical address.
• Physical address.
Size of(page)=size of(frame)
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Problem Statement
• Physical memory is growing exponentially
• But TLB size have grown slowly
 Limited TLB reach

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Recent work

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RMM design

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Components for RMM

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TLB operations in RMM design

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RMM node design with CR-RT register

10. • If memory is requested on demand, it may be assigned out of order.
• Demand paging allocates single pages even when large amount of physical
memory is available.
• Used in place of demand paging.
• Allocates contiguous memory.
• Similar to buddy paging.
Eager Paging
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Pseudocode of RMM memory allocator
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12. • Implemented in Linux kernel v3.15.5.
• RMM is defined with respect to Intel x86-64 Snady Bridge dual-socket Xeon E5-
2430 core.
• Chosen a 32-entry fully associative range TLB accessed in parallel with the L2
page TLB.
• Workloads with poor TLB performance from SPEC 2006, BioBench, Parsec, and
big-memory workload were selected.
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Evaluating RMM with different workloads
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Summary
 Redundant memory mappings is a robust translation
mechanism that improves performance by reducing cost
of virtual memory.
 RMM efficiently represents ranges of many pages that
are virtually and physically contiguous.
 RMM requires modest changes to existing hardware and
oprating system.
 The resulting system delivers a virtual memory system
that gives high performance, flexibility and completely
transparent to applications.
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Thank
you!
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