A page-fault occurs. No free frames are available. All entries in the page table have the dirty-bit set. What happens next?

Question

Accepted Answer

The page-fault causes a trap to kernel code. The kernel code invokes the page-replacement algorithm which chooses a page to evict from memory. Because the page is flagged as dirty, the data in the frame currently allocated to that page is copied out to backing store and the data for the requested page is then copied in to replace it. The page-table entry for the requested page is updated to point to the re-allocated frame, setting the valid bit and un-setting the dirty bit. The instruction that caused the page-fault is then restarted.

Answer

The page-fault causes a trap to kernel code. The kernel code invokes the page-replacement algorithm which chooses a page to evict from memory but, because all pages are flagged as dirty, no victim page can be chosen. In this (very rare) situation, the memory management system will fail, causing a "kernel panic" or "blue screen of death".

Answer

The page-fault causes a trap to kernel code. The kernel code invokes the page-replacement algorithm which chooses a page to evict from memory. Because the page is flagged as dirty, the data in the frame currently allocated to that page is discarded and the data for the requested page is then copied in to replace it. The page-table entry for the requested page is updated to point to the re-allocated frame, setting the valid bit and un-setting the dirty bit. The instruction that caused the page-fault is then restarted.

Answer

The page-fault causes a trap to kernel code. Because no free-frames are available, the process that caused the page-fault is terminated. All frames that were previously allocated in the page table are moved on to the free-frame list and the dirty-bits are all un-set.

Answer

The page-fault causes a trap to kernel code. Because the requested page is faulty, it is removed from the page-table, un-setting the dirty-bit and terminating the process that executed the offending instruction.

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A page-fault occurs. No free frames are available. All entries in the page table...

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