Memory management in android operating system

"Memory management in android operating system"








All routines are kept on disk in a re-locatable load format. A blue "Ex" label will then be present next to the processes name. Plan for a lot more QA than you ever expected. Not the phone or OS). Most of the time the memory leak occurs due to the same mistake: keeping a long-lived reference to a Context. Unlike either of these frameworks, the Android run time also manages the process lifetimes. Android ensures application responsiveness by stopping and killing processes as necessary to free resources for higher-priority applications. Bottomline To conclude the explanation, it only affects devices without external memory card. When it combines the libraries at load time, the linking is called static linking and when this linking is done at the time of execution, it is called as dynamic linking. Execution time -- If the process can be moved during its execution from one memory segment to another, then binding must be delayed to be done at run time Dynamic Loading In dynamic loading, a routine of a program is not loaded until it is called by the program. NET, Android uses its own run time and virtual machine to manage application memory. Dynamic loading makes better memory space utilization and unused routines are never loaded. Here are several tips: Understand potential sources of issues: if you know what not to do, you never need to know how to fix it. Inactive applications have been preloaded into memory, but are not actually using up any system resources. These are the processes Android is trying to keep responsive by reclaiming resources. Here's the rest if you're interested (highly recommended. Swapping is a mechanism in which a process can be swapped temporarily out of main memory to a backing store. The smallest hole that is big enough is allocated to program. Background Processes Processes hosting Activities that aren’t visible and that don’t have any Services that have been started are considered background processes. Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. By contrast, introduces less accessibility for the smartphone be used as an external memory. Motorola Xoom is the first Tablet PC running this OS. Having lots of available empty memory is not a good thing. The set of holes is searched to determine which hole is best to allocate. There will generally be a large number of background processes that Android will kill using a last-seen-first-killed pat - tern to obtain resources for foreground processes. Hence prevents a bug within a process from affecting other processes, or the operating system itself, and instead results in a segmentation fault or storage violation exception being sent to the disturbing process, generally killing of process. The best way to effectively pass timely, event-driven data around in Android ecosystems can be debated without end. It decides which process will get memory at what time. On Android, this is not the case. Sun has been pushing Java technology on mobiles for years, it was successfully deployed on most of the mobile phones, but lack of standardization made it difficult to reach the depths of Mobile phone market. Dalvik is an open source, register-based virtual machine (VM) that is part of the Android Operating System. Excluding Processes You can specifically exclude critical processes from being terminated when pressing the "End All" button. It takes the same amount of power to hold "nothing" in memory as it does to hold actual data. Active processes include: Activities in an “active” state; that is, they are in the foreground and responding to user events. In this chapter we will be learning about Architecture of android operating system. This will notify DDMS when a device is connected or disconnected. The End All button should only be used when absolutely necessary. Dynamic Linking Linking is the process of collecting and combining various modules of code and data into a executable file that can be loaded into memory and executed. This feature is beneficial in cases where you have important processes that you never want terminated even in the case where you have to use End All. Normally Java was used to create Java games on mobile; many other applications are still build on the native OS and not on the Java layer. Very thorough unit testing. The more applications Android can keep in memory, the faster it will be for the user to switch between his apps. But sometimes there is not enough main memory to hold all the currently active processes in a timesharing system. Today, the name Android operating system has become synonymous with a handheld device which can show movies, allow one to talk to another person, send messages, pictures, emails, play games and let you stay in touch with everybody. Any system which will require a simple, elegant and easy to develop User Interface might be built on Android framework. Some of these applications may be terminated manually, but they will be immediately restarted afterward by the OS. The internal memory of Ice Cream Sandwich is not divided between application memory and storage memory. MMU uses following mechanism to convert virtual address to physical address. DDMS provides services like screen capture on the device, threading, heap information on the device, logcat, processes, incoming calls, SMS checking, location, data spoofing, and many other things related to testing your Android application. This means that it closes the applications when the system needs more memory. Java is already available on majority of the mobile phones. Virtual and physical addresses differ in execution-time address-binding scheme. Generally speaking, you should only "End" applications if you see one which is not working correctly. Logical address is also known a Virtual address. Memory management keeps track of each and every memory location either it is allocated to some process or it is free. The OS may also preload applications into memory which it thinks might soon be needed. Services support ongoing processing that should continue without a visible interface. Android applications are limited to 16 MB of heaped memory. In theory, and up leaving an extremist view, this means that we have 16 GB of installed applications and files anything, which was impossible in previous versions of Android. It tracks whenever some memory gets freed or unallocated and correspondingly it updates the status. As such, there is no need to manually remove these applications, as you will see no tangible benefit from doing so. For example, if the base register holds 300000 and the limit register is 1209000, then the program can legally access all addresses from 300000 through 411999. The Linux kernel was chosen because it was proven to be stable and powerful. A systematic examination and evaluation of data or information is very important so that we can manage the available memory in an effective way. For example, if the base register value is 10000, then an attempt by the user to use address location 100 will be dynamically reallocated to location 10100. It checks how much memory is to be allocated to processes. A process needs to be in memory for execution. Current Java on mobile (J2ME) have a lot of limitation, so major mobile phone company add in their own extension to the Java library, this makes portability of Java application on mobile more difficult. Visible Processes Visible, but inactive processes are those hosting “visible” Activities. Using "End All" The "End All" button, shown on the home screen of the application, is used to terminate all running tasks. Sometimes complete program is loaded into the memory, but some times a certain part or routine of the program is loaded into the main memory only when it is called by the program, this mechanism is called Dynamic Loading. Android is a Mobile Operating System, developed By Android Inc. This differentiates ICS from others and removes the absurd limitation of current Android smartphones to install applications. The Dalvik VM executes files in the Dalvik Executable (. Main memory is also known as RAM. This is why all the widgets receive a Context parameter in their constructor. Its software stack and framework is built on Linux kernel, which has been very instrumental in its seamless acceptance as an OS of choice in Mobile phones. For this we have DDMS in Android Studio IDE, using which we can analyze the memory being utilized. The run-time mapping from virtual to physical address is done by the memory management unit (MMU) which is a hardware device. It is of three types : First Fit The first hole that is big enough is allocated to program. To do so, tap the process item and then tap the "Exclude" button. The free blocks of memory are known as holes. I will come soon with tracking the memory allocation and avoiding the memory leaks. I have a task killer installed only to kill unresponsive apps that the OS can't kill for whatever reason (which by the way, is a fault generally of the app's developer(s). Services that are executing an onStart, onCreate, or onDestroy event handler. Android will simply cache new applications into memory once it detects free memory is available. How to Use a Task Manager Android was designed from the ground up as an operating system (OS) for mobile devices. While Physical address is the address that actually exists on memory. The specialty of this version is that it is specially designed for tablet PCs. Dalvik and the Android run time sit on top of a Linux kernel that handles low-level hardware interaction including drivers and memory management, while a set of APIs provide access to all the under-lying services, features and hardware. But where do you start? And it is poised to become an all-encompassing framework which will be used not only on simple hand held devices like smart phones but its uses will also be on HDTV’s, Automotive Infotainment systems. Rather than use a traditional Java virtual machine (VM) such as Java ME (Java Mobile Edition), Android uses its own custom VM designed to ensure that multiple instances run efficiently on a single device. Utilize prayer, lucky rabbit feet, or indomitable willpower in the face of the inevitable flood of negative reviews when you ignore this issue. Also, at times the physical memory is broken into fixed size blocks and memory is allocated in unit of block sizes. It’s important to structure your application correctly to ensure that its priority is appropriate for the work it’s doing. On a desktop OS, like Windows, Mac OS X, or Ubuntu Linux, the user is responsible for closing programs in order to keep a reasonable amount of memory available. As a result of this, free holes exists to satisfy a request but is non contiguous i. The largest hole that is big enough is allocated to program. The most common scenario to warrant its use would be if your phone becomes very unresponsive and you are unable or do not have time to discern the cause. Page Table A Page Table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual address and physical addresses. Instructions and data to memory addresses can be done in following ways Compile time -- When it is known at compile time where the process will reside, compile time binding is used to generate the absolute code. Resources are simple files in xml format. Virtual and physical addresses are the same in compile-time and load-time address-binding schemes. Each segment in this scheme is divided into pages and each segment is maintained in a page table. On Android, every application runs in its own process, each of which hosts its own virtual machine (VM). For a new hardware mobile manufacturer, the first thing to do for building an Android platform is to build the device driver on the Linux kernel, there should be a lot of developers around who have the know-how to build the software stack from scratch or customize it from the available software. In such situation processes are loaded and removed from the memory. This formed base for many doubts so, we try to clear them with all the information gathered in this regard. The difference between allocated and required memory is known as Internal fragmentation i. Operating system can link system level libraries to a program. Unlike either of these frameworks, the Android run time also manages the lifetime processes. The value in the base register is added to every address generated by a user process which is treated as offset at the time it is sent to memory. U nderstanding Application Priority and Process States The order in which processes are killed to reclaim resources is determined by the priority of the hosted applications. An active application may be running in the background and not have any information currently displayed on the screen. In such a case, rather than loading all the dependent programs, CPU links the dependent programs to the main executing program when its required. Android has a very reach and standardized set of API’s and libraries, developers can use those API to develop games and applications, integrate well into mobile phones, and Java will make Android application portable on all (Android) mobile phones. And each process listens for a debugger on a different port. And, in fact, it often is. As such, using the task manager feature of SystemPanel to constantly clear memory by killing all apps is strongly NOT RECOMMENDED. It is generally termed as inability to use the available memory. Process Types The SystemPanel process listing groups applications into three categories: "Active", "Inactive", and "Internal": Active applications are actually running at the present time on the device. The use of MTP. Because of this and the fact that Java apps can be effortlessly built through SDK’s the applications are portable on all mobile devices. Each Android application runs in a separate process within its own Dalvik instance, relinquishing all responsibility for memory and process management to the Android run time, which stops and kills processes, necessary to manage resources. Segmentation Segmentation is another memory management scheme that supports the user-view of memory. If you don’t, your application could be killed while it’s in the middle of something important. One method is attaching an implementation of an interface definition to the object sending the data, and holding that implementation within the receiver object. Memory allocation is a process by which computer programs are assigned memory or space. The set of all physical addresses corresponding to these logical addresses is referred to as a physical address space. An Android Debugger is used for debugging the Android app and starts a device monitoring service between the two. It must be capable of providing direct access to these memory images. In particular, part 2 does a great job of explaining how Android (and really Linux) is different then most people's OS experience. Such behavior is normal, will improve performance of the phone, and will not cause additional battery drain. The computer is able to change only data that is in main memory. Since, Ice Cream Sandwich if natively supports the USB Mass Storage Class protocol. So, excess process are kept on disk and brought in to run dynamically. I think, Now you might be clear the memory concept of android. Swapping is the process of bringing in each process in main memory, running it for a while and then putting it back to the disk. This mechanism is known as Dynamic Linking. The combined scheme is known as 'Page the Elements'. Internal applications are those which are part of the Android operating system itself. All Android applications will remain running and in memory until the system needs its resources for other applications. Since the library runs on top of the Linux kernel, there are a lot of drivers and libraries available which can be customized as per the vendor’s requirement. Android is built on top of Linux 2. Java language was chosen as the development language. There are generally very few visible processes, and they’ll only be killed in extreme circumstances to allow active processes to continue. Fragmentation Fragmentation occurs in a dynamic memory allocation system when most of the free blocks are too small to satisfy any request. Basically Android can make any app run as long as it can be converted to Dalvik byte code. It relies on the Linux kernel for threading and low-level memory management. When a device is connected, a VM monitoring service is created between ADB and DDMS, which will notify DDMS when a VM on the device is started or terminated. NET, Android uses its own run time and virtual machine to manage application memory. Features of DDMS DDMS connects the IDE to the applications running on the device. Segmentation with Paging Both paging and segmentation have their advantages and disadvantages, it is better to combine these two schemes to improve on each. Each Android application runs in a separate process within its own Dalvik instance, relinquishing all responsibility for memory and process management to the Android run time, which stops and kills processes as necessary to manage resources. There are generally very few of these processes, and they will be killed only as a last resort. By technical point of view, Android using Java over Linux is a smart move. Nokia has an Internet Table device (N770) which was build using Linux operating system too. Android maintains this cache to improve the start-up time of applications when they’re re-launched. Load time -- When it is not known at compile time where the process will reside in memory, then the compiler generates re-locatable code. All the programs are loaded in the main memeory for execution. The main program is loaded into memory and is executed. The memory used by these applications can be immediately reclaimed should other applications require it. Total transfer time is directly proportional to the amount of memory swapped. Other routines methods or modules are loaded on request. The base register holds the smallest legal physical memory address and the limit register specifies the size of the range. Dalvik and the Android run time sit on top of a Linux kernel that handles low-level hardware interaction including drivers and memory management, while a set of APIs provides access to all of the under - lying services, features, and hardware. As the name suggests, visible Activities are visible, but they aren’t in the foreground or responding to user events. The Dalvik VM executes Dalvik executable files, a format optimized to ensure minimal memory foot - print. The set of all logical addresses generated by a program is referred to as a logical address space. In static linking, libraries linked at compile time, so program code size becomes bigger whereas in dynamic linking libraries linked at execution time so program code size remains smaller. This phenomenon is known as External Fragmentation. What is MTP The use of MTP instead of the usual MSC (Mass Storage Class) implies certain advantages for users who regularly use Windows, particularly Windows Media Player. Memory Protection Memory protection is a phenomenon by which we control memory access rights on a computer. Memory is divided into several fixed size partitions. Its built-in application and memory-management systems were engineered with battery life as one of the most critical concerns. Linux Kernel provides the basic system functionality such as process management, memory management and device management Linux kernel also provides array of device drivers which make our task easier while interfacing the android with peripheral devices. They are still considered to be foreground processes and won’t be killed unless resources are needed for active or visible processes. Usually a lot of memory is used for a phone and very little memory is left for what some developers want to achieve. The Android OS does not work like a desktop operating system. However, this improvement comes with its drawbacks, namely that the absence of internal divisions, the memory space is seen as a whole System and does not allow it to be mounted as a storage unit while it is connected via USB. There were a lot of companies trying to build mobile phone operating system based on Linux kernel before Android did, but have not been very successful. Both Java and Linux are proven technology, and provide portability for mobile application on Android platform. Also, at times one program is dependent on some other program. Here physical memory is divided into blocks of equal size called Pages. Holding down the End All button will terminate all running applications, but will not attempt to terminate system-level processes. On Android, a Context is used for many operations, but mostly to load and access resources. Dalvik Virtual Machine Dalvik is a register-based virtual machine that’s been optimized to ensure that a device can run multiple instances efficiently. Contiguous Memory Allocation In contiguous memory allocation each process is contained in a single contiguous block of memory. With the unified storage model introduced in Honeycomb, you get full 32GB (or 16GB or whatever) between app data and media data. Virtual address is also known as Logical address and is generated by the CPU. Memory management provides protection by using two registers, a base register and a limit register. The pages belonging to a certain process are loaded into available memory frames. There are a lot of mobile developers who are well versed in Java and hence can have a seamless transition to writing Mobile apps and widgets on Android powered Smart phones Java is a proven technology, portable on different software and hardware platform. The following list details each of the application states shown in Figure. Such applications will not consume any battery power whatsoever. Even Motorola and Nokia had released some mobile and internet devices which run on Linux operating system, but they were not very successful as well, like the Motorola A series phone started with A760. However, most android users are not very satisfied with how it does its things because sometimes it leaves too many processes running which causes sluggishness’ in everyday performance. Tapping the button will open a menu allowing you to choose the "severity" of the operation, e. The Dalvik Virtual Machine One of the key elements of Android is the Dalvik virtual machine. As a developer, we often run into memory leaks issues in Android applications. Process priority is also affected by interprocess dependencies; if an application has a dependency on a Service or Content Provider supplied by a second application, the secondary application will have at least as high a priority as the application it supports. By using a VM to host application execution, developers have an abstraction layer that ensures they never have to worry about a particular hardware implementation. The user program deals with virtual addresses; it never sees the real physical addresses. The Dalvik VM uses the device’s underlying Linux kernel to handle low-level functionality including security, threading, and process and memory management. An application’s priority is equal to its highest-priority component. The OS itself automatically removes programs from memory as memory is needed. Attempting to constantly use "End All" to keep memory free will however cause the phone to have to do more work (reloading applications), which can actually have a negative impact on your battery life. Activities, Services, or Broadcast Receivers that are currently executing an onReceive event handler. Paging is a memory management mechanism that allows the physical address space of a process to be non-contagious. As of Android 2. You will explore Activity states in greater detail later in this chapter. Let us assume that the user process is of size 100KB and the backing store is a standard hard disk with transfer rate of 1 MB per second. Empty Processes To improve overall system performance, Android often retains applications in memory after they have reached the end of their lifetimes. When a partition is free, a process is selected from the input queue and loaded into it. Logical versus Physical Address Space An address generated by the CPU is a logical address whereas address actually available on memory unit is a physical address. Each partition contains exactly one process. The main aim of it is to prevent a process from accessing memory that has not been allocated to it. The word main is used to distinguish it from external mass storage devices such as disk drives. In a regular Android application, you usually have two kinds of Context – Activity and Application. Android studio includes a debugging tool called the Dalvik Debug Monitor Service (DDMS). These processes are rou - tinely killed as required. The memory allocated to a space may be slightly larger than the requested memory. Even if you do not plan on using all of this memory, you should use memory as little as possible to let other applications run without getting them killed. Because Services don’t interact directly with the user, they receive a slightly lower priority than visible Activities. The Java program doesn’t run directly on Android, it is converted into Dalvik byte code. This happens when an Activity is only partially obscured (by a non-full-screen or transparent Activity). Started Service Processes Processes hosting Services that have been started. Where two applications have the same priority, the process that has been at a lower priority longest will be killed first. Segmentation allows breaking of the virtual address space of a single process into segments that may be placed in non-contiguous areas of physical memory. It uses native open source C libraries which power Linux machines. Major time consuming part of swapping is transfer time. Therefore, every program we execute and every file we access must be copied from a storage device into main memory. A solution to fragmentation problem is Paging. There are a great many misconceptions about how Android works with regard to starting and stopping applications. All Android hardware and system service access is managed using Dalvik as a middle tier. Android is perhaps one of the most used Operating System cum framework available for what we call smartphones today.