CODEWITHSUNDEEP
linuxmemorymemory-managementoperating-systempage-fault
Dan
Dan

Reputation: 99

Page Table Entry, Present Bit?

Quoting from: http://www.cburch.com/books/vm/index.html

The final bit (labeled P) indicates whether the page is present in RAM. If this bit is 0, then any access to the page will trigger a page fault.

My professor doesn't agree, he said the bit can be 0 while page is in RAM and he added that this can happen when the page is shared between multiple processes and someone does something or so.

Can someone kindly explain this, still I don't get it I'm looking for detailed examples when page is in RAM but it's present bit in PTE is 0 and not 1.

Upvotes: 1

Views: 652

Answers (1)

Neeraj
Neeraj

Reputation: 1

Yes, It's possible to have a page in RAM with p-bit disabled. This method was useful while creating a software/kernel with multi-threading and multi-processor environment, where a process needs exclusive rights or if a piece code must not cross some other. We can temporarily disable it's access to other core/processor by demoting p-bit in page-table and the kernel/software must handle the page fault accordingly.

Upvotes: 0

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