Modern Operating Systems by Herbert Bos ...
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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 265
for them. Space has to be allocated in memory for the page table and it has to be
initialized. The page table need not be resident when the process is swapped out
but has to be in memory when the process is running.
In addition, space has to be
allocated in the swap area on disk so that when a page is swapped out, it has some-
where to go. The swap area also has to be initialized with program text and data so
that when the new process starts getting page faults, the pages can be brought in.
Some systems page the program text directly from the executable file, thus saving
disk space and initialization time. Finally, information about the page table and
swap area on disk must be recorded in the process table.
When a process is scheduled for execution, the MMU has to be reset for the
new process and the TLB flushed, to get rid of traces of the previously executing
process. The new process’ page table has to be made current, usually by copying it
or a pointer to it to some hardware register(s). Optionally, some or all of the proc-
ess’ pages can be brought into memory to reduce the number of page faults ini-
tially (e.g., it is certain that the page pointed to by the program counter will be
When a page fault occurs, the operating system has to read out hardware regis-
ters to determine which virtual address caused the fault. From this information, it
must compute which page is needed and locate that page on disk.
It must then find
an available page frame in which to put the new page, evicting some old page if
need be. Then it must read the needed page into the page frame.
Finally, it must
back up the program counter to have it point to the faulting instruction and let that
instruction execute again.
When a process exits, the operating system must release its page table, its
pages, and the disk space that the pages occupy when they are on disk.
If some of
the pages are shared with other processes, the pages in memory and on disk can be
released only when the last process using them has terminated.
3.6.2 Page Fault Handling
We are finally in a position to describe in detail what happens on a page fault.
The sequence of events is as follows:
The hardware traps to the kernel, saving the program counter on the
stack. On most machines, some information about the state of the
current instruction is saved in special CPU registers.
An assembly-code routine is started to save the general registers and
other volatile information, to keep the operating system from destroy-
ing it. This routine calls the operating system as a procedure.
3. The operating system discovers that a page fault has occurred, and
tries to discover which virtual page is needed. Often one of the hard-
ware registers contains this information.
If not, the operating system

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