The maximum amount of physical memory currently supported by Windows	ranges from 2 GB to 24 TB
the memory manager has two primary tasks	Translating, or mapping, a process’s virtual address space into physical memory Paging some of the contents of memory to disk when it becomes overcommitted
Translating, or mapping, a process’s virtual address space into physical memory	when a thread running in the context of that process reads or writes to the virtual address space, the correct physical address is referenced.
Paging some of the contents of memory to disk when it becomes overcommitted	when running threads try to use more physical memory than is currently available—and bringing the contents back into physical memory when needed.
HAL	Hardware Abstraction Layer: layer of software that interacts between the hardware and the rest of the operating system
What is the Memory manager?	it is part of the Windows executive and therefore exists in the file Ntoskrnl.exe
Components of the memory manager	A set of executive systems in charge of allocate and deallocate virtual memory A fault trap, to handle the memory exceptions *Six key top-level routines running in their own thread
The six key top-level routines of the memory manager	The balance set manager (keBalanceSetManager, priority 17) The process/stack swapper (KeSwapProcessOrStack, priority 23) The modified page writer (MiModifiedPageWriter, Priority 18) The mapped page writer (MiMapedPageWriter, priority 18) The segment deference thread (MiDeferenceSegmentThread, priority 19) The zero page thread (MiZeroPageThread, priority 0)
The balance set manager	This calls an inner routine, the working set manager (MmWorkingSetManager), once per second as well as when free memory falls below a certain threshold.
The working set manager	drives the overall memorymanagement policies, such as working set trimming, aging, and modified page writing.
What does the The process/stack swapper?	This performs both process and kernel thread stack inswapping and outswapping.
What does the modified page writer?	This writes dirty pages on the modified list back to the appropriate paging files.
What does The mapped page writer	This writes dirty pages in mapped files to disk or remote storage.
What does the segment dereference thread	This is responsible for cache reduction as well as for page file growth and shrinkage.
What does the zero page thread	This zeroes out pages on the free list so that a cache of zero pages is available to satisfy future demand-zero page faults.
Page size	x86, 4KB→ 2MB =512 x64, 4KB→ 2MB=512 ARM, 4KB→ 4MB=1024
Primary advantage of large pages	Speed, it uses less TLB´s to translating the adresses
TLB	Translation look-aside buffer, contains the first byte within the page, and iy uses it to translate the adresses into physical memory
What does Windows map?	Windows maps with large pages the core operating system images as well as core operating system data. Windows allows to the applications to map their images, private memory and page file-backed sections with large pages
What could make the attemptps to allocate large pages fail?	When the operating system has been running for a long time, because a large page uses a large amount of contiguous small pages, and memory could become fragmented, this may not affect small pages, but will affect large pages.
Huge pages	Pages of 1GB of size, if a allocation request needs more than one huge page, it could use one plus some other larger pages
Disadvantage of large pages	If a block of read only code is put along with a writable part of code, the whole page is marked as write/read page, and a malicious attempt, or just a bug, could modify a critical part of the code and the respective memory access violation won´t appear.
VMMap	This shows the usage of virtual memory within a process to a fine level of detail.
RAMMap	This shows detailed physical memory usage.
!vm command	Shows the basic memory management information available through the memory related performance counters. This command can be useful if you’re looking at a crash dump or hung system.
Internal synchronization	The memory manager supports simultaneous execution on multiprocessors systems
Some of the resources which the memory manager must control access	■Dynamically allocated portions of the system virtual address space ■ System working sets ■ Kernel memory pools ■ The list of loaded drivers ■ The list of paging files ■ Physical memory lists ■ Image base randomization address space layout randomization (ASLR) structures ■ Each individual entry in the page frame number (PFN) database
Working set lock	Needs synchronization, This is held while changes are made to the working set list.
Address space lock	Needs synchronization, This is held whenever the address space is being changed.
State	is a particular arrangement of bits. For example, if you have four bits in your memory, 0110, 0001, and 1011 represent three different states
image	particular physical arrangement of bits.
Tasks of kernel´s memory management	• The kernel must have its own private area in memory that user processes can’t access. • Each user process needs its own section of memory. • One user process may not access the private memory of another process. • User processes can share memory. • Some memory in user processes can be read-only. • The system can use more memory than is physically present by using disk space as auxiliary.
MMU	Memory Manage Unit, translates the virtual memory addresses used by processes into real ones
page table	The implementation of a memory address map
on-demand paging	A user process does not actually need all of its pages to be immediately available in order to run. The kernel generally loads and allocates pages as a process needs them
page fault	a memory page is not ready when a process wants to use it, the process triggers it
Minor Page Faults	occurs when the desired page is actually in main memory but the MMU doesn’t know where it is. This can happen when the process requests more memory or when the MMU doesn’t have enough space to store all of the page locations for a process.
Major Page Faults	occurs when the desired memory page isn’t in main memory at all, which means that the kernel must load it from the disk or some other slow storage mechanism.
command "time"	displays page faults
command "top"	Shows the page faults of processes as they’re running
command "ps"	you can use a custom output format to view the page faults for a particular process
vmstat procs	for processes
vmstat memory	for memory usage *The buff column indicates the amount of memory that the kernel is using for disk buffers
vmstat swap	for the pages pulled in and out of swap * si (swap-in) * so (swap-out)
vmstat io	for disk usage
vmstat system	for the number of times the kernel switches into kernel code
vmstat cpu	for the time used by different parts of the system us= the percentage of time that the CPU is spending on user tasks, sy = system (kernel) tasks, id = idle time wa = waiting for I/O

Descubre

Crear Tarjetas

Acerca de Nosotros

Explore Tarjetas

Comparta este Set de Tarjetas de Aprendizaje

Tarjetas de Aprendizaje relacionadas

Sistemas Operativos

Cómo estudiar sus tarjetas

Rango de Cartas a estudiar

47 Cartas en este set