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Is there a page table for each process?
Each process has its own page table in the kernel. Having a separate page table for each process is necessary for process isolation as they should not be allowed to stomp on each others memory. Since each process has a different page table, there is not one pmap that will work for every process.
What does a page table do in a process?
Page table translates from virtual to physical page addresses. Since each process has its own virtual address space and usually maps the same virtual address to a different physical address it needs a separate page table. Curiously, multiple processes may map different virtual addresses to the same physical memory.
What can be applied into a page table to detect whether pages in memory or not?
Pages can be paged in and out of physical memory and the disk. The present bit can indicate what pages are currently present in physical memory or are on disk, and can indicate how to treat these different pages, i.e. whether to load a page from disk and page another page in physical memory out.
What is stored in a page table entry?
A page table entry contains information about an individual page in a process’s logical address space. It typically has a size of 4 bytes (32 bits). It contains two kinds of information: Bits to represent the frame number.
Are page tables stored in cache?
The CPU’s memory management unit (MMU) stores a cache of recently used mappings from the operating system’s page table. This is called the translation lookaside buffer (TLB), which is an associative cache. When a virtual address needs to be translated into a physical address, the TLB is searched first.
How many bits are required for each page table entry?
44 bits
So, each entry is at least 44 bits (6 bytes for byte-aligned, 8 bytes for word-aligned). Each top-level page table is therefore 256*6 = 1536 bytes (256 * 8 = 2048 bytes).
How are page tables maintained by each process?
The page tables are managed by the kernel, and indeed various processes may use different -or sometimes same- page tables. (So context switches managed by the kernl may need to reconfigure the MMU). You don’t care, (and the user processes don’t see page tables) the kernel will manage them.
What do page table entries do in PTE?
Page table has page table entries where each page table entry stores a frame number and optional status (like protection) bits. Many of status bits used in the virtual memory system. The most important thing in PTE is frame Number. Page table entry has the following information –
How to examine process page tables in Linux?
Select the maps you are interested in – all of them, or a particular library, or the stack or the heap, etc. Open /proc/pid/pagemap and seek to the pages you would like to examine. Read a u64 for each page from pagemap.
How many entries does a page table need?
The page table needs one entry per page. Assuming a 4GB (2^32 byte) virtual and physical address space and a page size of 4kB (2^12 bytes), we see that the the 2^32 byte address space must be split into 2^20 pages. This means the page table must have 2^20 entries.