On Thu, 15 Nov 2018 23:53:56 +0800, "Larry" said:
I'm curious when multiple process has the same PTE which points to the samepage, how can kernel differenciate which page from swap space should be swappedin?
The PTE tells where in /dev/swap to find the page. If it's a shared page, the references all point at the same place, so "process 1's PAGE_A info" is the same as "process 2's PAGE_A" info. They may have different addresses in the two processes, but they're both referencing the same swap page.
Process 2 get scheduled, PAGE_A was from Process 1, so it should be swapped out
Why? In general, there's no need to do so - and if it's shared, it's probably a hot page so it won't be chosen for swapout. (Remember - the kernel doesn't do swapin/swapout decisions in schedule(), it only takes action once Process 2 starts running and references a page that requires something be done.