I am using a VM with Ubuntu and am looking at memory managment and wanted to kno
ID: 3665803 • Letter: I
Question
I am using a VM with Ubuntu and am looking at memory managment and wanted to know why some of the values changed after I opened a few applications like Firefox and LibreOffice Writer so I understand. The ones I need to know about are amount of memory used by buffers in the kernel, size of the page cache (Memory used for holding physical memory page tables), amount of memory containing “dirty” pages, and the amount of memory being used for page tables, and the number of shared Memory Segments. Also what is the page cache, page tables, resident memory, and what is shared memory and talk about the command used to view shared memory segement information.
Explanation / Answer
(i)Page cache
Page cache of data residing on a storage device, kept by the operating systems and stored in unused main memory.
(ii)Page tables
A page table is the data structure used as memory management technique to store the mapping between virtual addresses and physical addresses.
(iii)Resident memory
A resident memory is a portion of memory occupied by a process that is held in main memory.
(iv)Shared memory
Shared memory is memory that is accessible to a number of processes. By several orders of magnitude, it is the quickest way of sharing information among a set of processes. Keep in mind that shared memory is available on all operating systems. Only the calls will be different.
command used to view shared memory segement information:
The ipcs -mS command can be used to view all shared memory segments that have been allocated on the entire system, and the svmon -P <PID> command can be used to view shared memory segments that are currently being used by a specific process.
Buffer Cache, is often used for the Page Cache. Linux kernels up to version 2.2 had both a Page Cache as well as a Buffer Cache. As of the 2.4 kernel, these two caches have been combined. Today, there is only one cache, the Page Cache
Functional Approach:
Memory Usage
Under Linux, the number of megabytes of main memory currently used for the page cache is indicated in the Cached column of the report produced by the free -m command.
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