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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 284
SEC. 3.8
RESEARCH ON MEMORY MANAGEMENT
253
paging for performance (Lee et al., 2013), and latency reasons (Saito and Oikawa,
2012), and because they wear out if used too much (Bheda et al., 2011, 2012).
More generally, research on paging is still ongoing, but it focuses on newer
kinds of systems.
For example, virtual machines have rekindled interest in mem-
ory management (Bugnion et al., 2012).
In the same area, the work by Jantz et al.
(2013) lets applications provide guidance to the system with respect to deciding on
the physical page to back a virtual page.
An aspect of server consolidation in the
cloud that affects paging is that the amount of physical memory available to a vir-
tual machine can vary over time, requiring new algorithms (Peserico, 2013).
Paging in multicore systems has become a hot new area of research (Boyd-
Wickizer et al., 2008, Baumann et al., 2009).
One contributing factor is that multi-
core systems tend to have a lot of caches shared in complex ways (Lopez-Ortiz and
Salinger, 2012). Closely related to this multicore work is research on paging in
NUMA systems, where different pieces of memory may have different access
times (Dashti et al., 2013; and Lankes et al., 2012).
Also, smartphones and tablets have become small PCs and many of them page
RAM to ‘‘disk,’’ only disk on a smartphone is flash memory.Some recent work is
reported by Joo et al. (2012).
Finally, interest is memory management for real-time systems continues to be
present (Kato et al., 2011).
3.9 SUMMARY
In this chapter we have examined memory management.
We saw that the sim-
plest systems do not swap or page at all.
Once a program is loaded into memory, it
remains there in place until it finishes. Some operating systems allow only one
process at a time in memory, while others support multiprogramming.
This model
is still common in small, embedded real-time systems.
The next step up is swapping. When swapping is used, the system can handle
more processes than it has room for in memory. Processes for which there is no
room are swapped out to the disk.
Free space in memory and on disk can be kept
track of with a bitmap or a hole list.
Modern computers often have some form of virtual memory.
In the simplest
form, each process’ address space is divided up into uniform-sized blocks called
pages, which can be placed into any available page frame in memory. There are
many page replacement algorithms; two of the better algorithms are aging and
WSClock.
To make paging systems work well, choosing an algorithm is not enough;
attention to such issues as determining the working set, memory allocation policy,
and page size is required.
Segmentation helps in handling data structures that can change size during ex-
ecution and simplifies linking and sharing.
It also facilitates providing different
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