Thrashing is a high paging activity.A process is thrashing
if it is spending more time with paging rather than execution.
* global replacement algorithm.
* under allocation of the minimum
number of pages required by a process.
* very high degree of multiprogramming.
*reducing level or degree of multiprogramming.
*use local replacement algorithm.
*while allocating check minimum sufficient frame required
for a process.
Thrashing is caused by under allocation of the minimum
number of pages required by a process, forcing it to
continuously page fault. The system can detect thrashing by
evaluating the level of CPU utilization as compared to the
level of multiprogramming. It can be eliminated by reducing
the level of multiprogramming.
If the number of frames allocated to a low priority process
is lower than the minimum number required by the computer
architecture then in this case we must suspend the
execution of this low priority process.After this we should
page out all of its remaining pages and freeing all of its
allocated frames.This provision introduces a swap in,swap-
out level of intermediate CPU scheduling.Let take a example
of a process that does not have enough number of frames.If
the process does not have the number of frames it needs to
support pages in active use, it will quickly page fault.The
oly option remains here for process is to replace some
active pages with the page that requires a
frame.However,since all of its pages are in active use,it
must replace a page that will be needed again right
away.Consequently,it quickly faults again and again that
mean replacing pages that it must bring back in
immediately.This high paging activity is called
Thrashing.Or we can say that a process is Thrashing if it
is spending more time in paging then executing.Thrashing
results in severe performance problems.
Thrashing is the process of encountering frequent page
faults on replacing the existing pages in the main memory
with the new ones being referenced by the process.In this
the process on a system require more memory than it has.
- Each time one page is brought in,another page, whose
contents will soon be referenced, is thrown out.
-Processes will spend all of their time blocked, waiting for
pages to be fetched from disk.
-I/O devices at 100% utilization but system not getting much
of useful work done.
Thrasing occours when a system spends more time
processingpage fault than executing transsction.thrashing
has negative effect on the system that's why it becomes a
greater threat. CPU utilization reaches maximun before a
swift decline as the degree of multiprogramming increases
and thrasing occours in overextended system.
there are two technique for avoiding thrashing:
2.page fault rate
Thrashing is a concept in which a process spends its time in
searching of pages rather then execution the page required
so, A large process assigned a less no of frames
CAUSEes of thrashing:
as we increase the degree of multiprogramming the cpu
utilization is increasing and decrease after certain time
thrashing is said to occur when the system spends a large
amount of time transferring shared data blocks from one
node to another ,compared to the time spent doing the
useful work of executing application processes.
A process may not have enough frame.there is some number of
pages in active use.if process does not have this number of
frame,it will quickly page faults.at this point it must
replace some page.this high paging activity is thrashing.