<< Chapter < Page Chapter >> Page >

Need dynamic memory allocation both for main memory and for file space on disk.

Two basic operations in dynamic storage management:

  • Allocate
  • Free

Dynamic allocation can be handled in one of two general ways:

  • Stack allocation (hierarchical): restricted, but simple and efficient.
  • Heap allocation: more general, but less efficient, more difficult to implement.

Stack organization: memory allocation and freeing are partially predictable (as usual, we do better when we can predict the future).Allocation is hierarchical: memory is freed in opposite order from allocation. If alloc(A) then alloc(B) then alloc(C), then it must be free(C) then free(B)then free(A).

  • Example: procedure call. Program calls Y, which calls X. Each call pushes another stack frame on top of the stack. Each stack frame has space forvariable, parameters, and return addresses.
  • Stacks are also useful for lots of other things: tree traversal, expression evaluation, top-down recursive descent parsers, etc.

A stack-based organization keeps all the free space together in one place.

Heap organization: allocation and release are unpredictable. Heaps are used for arbitrary list structures, complex dataorganizations. Example: payroll system. Do not know when employees will join and leave the company, must be able to keep track of all them using the leastpossible amount of storage.

  • Inevitably end up with lots of holes. Goal: reuse the space in holes to keep the number of holes small, their size large.
  • Fragmentation: inefficient use of memory due to holes that are too small to be useful. In stack allocation, all the holes are together in one bigchunk.
  • Refer to Knuth volume 1 for detailed treatment of what follows.
  • Typically, heap allocation schemes use a free list to keep track of the storage that is not in use. Algorithms differ in how they manage the freelist.
    • Best fit: keep linked list of free blocks, search the whole list on each allocation, choose block that comesclosest to matching the needs of the allocation, save the excess for later. During release operations, merge adjacent free blocks.
    • First fit: just scan list for the first hole that is large enough. Free excess. Also mergeon releases. Most first fit implementations are rotating first fit.
  • Bit Map: used for allocation of storage that comes in fixed-size chunks (e.g. disk blocks, or 32-byte chunks). Keep a large array of bits, onefor each chunk. If bit is 0 it means chunk is in use, if bit is 1 it means chunk is free. Will be discussed more when talking about file systems.

Pools: keep a separate allocation pool for each popular size. Allocation is fast, no fragmentation.

Reclamation Methods: how do we know when memory can be freed?

  • It is easy when a chunk is only used in one place.
  • Reclamation is hard when information is shared: it cannot be recycled until all of the sharers are finished. Sharing is indicated by thepresence of pointers to the data (show example). Without a pointer, cannot access (cannot find it).

Two problems in reclamation:

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Operating systems' conversation and receive update notifications?

Ask