Memory Zone App [TOP] Download

I have inserted a 32GB SanDisk SD card in my Neuropad2 tablet (Cortex A8 processor, 8GB internal memory, -Neuropad2-Tablet-Capacitive-preinstalled/dp/B0076NR2F0/ref=/ref=cm_cd_f_pb_t) after having it FAT32 formatted. The SD card is correctly mounted, I can save files on it via ES File Explorer under \mnt\extsd, and I can see it on my Windows Explorer when the tablet is connected via USB in USB mass storage mode.

I want to up project locally. When I try to use php-fpm with this line fastcgi_pass unix:/run/php/php7.0-fpm.sock; then nginx doesn't reload, it exits with error: nginx: [emerg] zero size shared memory zone "one".

Memory Zone App Download

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SanDisk Memory Zone is a memory management utility for Android. The application is designed to help you take control of your internal memory, SD card memory, and even your cloud-based storage.

There are plenty of ways in which SanDisk Memory Zone can help you manage your files. The app gives you an overview of the remaining internal memory on your device, on your SD card, and on online storage services such as Google Drive, Dropbox, OneDrive, Picasa, and Facebook.

A neat feature of SanDisk Memory Zone is that it lets you easily download files from your cloud storage accounts and move them to your SD card or internal memory. Equally, you can upload files stored on your phone to your online storage.

The user interface of SanDisk Memory Zone is very attractive. I love the memory overview graphic, which provides a great visual view of what is eating into your storage. The file viewer interface is colorful and friendly, and you can slide between the different file type lists with a simple swipe.

Linux is available for a wide range of architectures so there needs to be anarchitecture-independent way of describing memory. This chapter describesthe structures used to keep account of memory banks, pages and the flagsthat affect VM behaviour.

Each node is divided up into a number of blocks calledzones which represent ranges within memory. Zones shouldnot be confused with zone based allocators as they are unrelated. A zone isdescribed by a struct zone_struct, typedeffedto zone_t and each one is of type ZONE_DMA,ZONE_NORMAL or ZONE_HIGHMEM. Each zone typesuitable a different type of usage. ZONE_DMA is memory in the lowerphysical memory ranges which certain ISA devices require. Memory withinZONE_NORMAL is directly mapped by the kernel into the upper regionof the linear address space which is discussed further in Section 4.1. ZONE_HIGHMEMis the remaining available memoryin the system and is not directly mapped by the kernel.

It is important to note that many kernel operations can only take place usingZONE_NORMAL so it is the most performance critical zone. Zones arediscussed further in Section 2.2. Each physical page frame isrepresented by a struct page and all the structs are kept in aglobal mem_map array which is usually stored at the beginningof ZONE_NORMAL or just after the area reserved for the loaded kernelimage in low memory machines. struct pages are discussed indetail in Section 2.4 and the global mem_maparray is discussed in detail in Section 3.7. The basic relationship betweenall these structs is illustrated in Figure 2.1.

As the amount of memory directly accessible by the kernel (ZONE_NORMAL)is limited in size, Linux supports the concept of High Memorywhich is discussed further in Section 2.5. This chapterwill discuss how nodes, zones and pages are represented before introducinghigh memory management.

As we have mentioned, each node in memory is described by apg_data_t which is a typedef for a structpglist_data. When allocating a page, Linux uses anode-local allocation policy to allocatememory from the node closest to the running CPU. As processes tend to runon the same CPU, it is likely the memory from the current node will be used.The struct is declared as follows in :

Zones are described by a struct zone_struct andis usually referred to by it's typedef zone_t. Itkeeps track of information like page usage statistics, free area informationand locks. It is declared as follows in :

Each zone has three watermarks called pages_low,pages_min and pages_high which help trackhow much pressure a zone is under. The relationship between themis illustrated in Figure 2.2. The numberof pages for pages_min is calculated in the functionfree_area_init_core() during memory init and is based on aratio to the size of the zone in pages. It is calculated initially asZoneSizeInPages / 128. The lowest value it will be is 20 pages(80K on a x86) and the highest possible value is 255 pages (1MiB on a x86).

The PFN is an offset, counted in pages, within the physical memory map. Thefirst PFN usable by the system, min_low_pfn is located at thebeginning of the first page after _end which is the end ofthe loaded kernel image. The value is stored as a file scope variable inmm/bootmem.c for use with the boot memory allocator.

How the last page frame in the system, max_pfn, iscalculated is quite architecture specific. In the x86 case, the functionfind_max_pfn() reads through the whole e820 map forthe highest page frame. The value is also stored as a file scope variable inmm/bootmem.c. The e820 is a table provided by the BIOS describingwhat physical memory is available, reserved or non-existent.

The value of max_low_pfn is calculated on the x86with find_max_low_pfn() and it marks the end ofZONE_NORMAL. This is the physical memory directly accessible by thekernel and is related to the kernel/userspace split in the linear addressspace marked by PAGE_OFFSET. The value, with the others,is stored in mm/bootmem.c. Note that in low memory machines,the max_pfn will be the same as the max_low_pfn.

With the three variables min_low_pfn, max_low_pfnand max_pfn, it is straightforward to calculate thestart and end of high memory and place them as file scope variablesin arch/i386/mm/init.c as highstart_pfn andhighend_pfn. The values are used later to initialise the highmemory pages for the physical page allocator as we will much later in Section5.5.

When IO is being performed on a page, such are during page-in or page-out, itis locked to prevent accessing it with inconsistent data. Processes wishingto use it have to join a wait queue before it can be accessed by callingwait_on_page(). When the IO is completed, the page will beunlocked with UnlockPage() and any process waiting on the queuewill be woken up. Each page could have a wait queue but it would be veryexpensive in terms of memory to have so many separate queues so instead,the wait queue is stored in the zone_t.

The zones are initialised after the kernel page tables have been fully setupby paging_init(). Page table initialisation is coveredin Section 3.6. Predictably, each architectureperforms this task differently but the objective is always the same, todetermine what parameters to send to either free_area_init()for UMA architectures or free_area_init_node() for NUMA. Theonly parameter required for UMA is zones_size. The full listof parameters:

It is the core function free_area_init_core() which is responsiblefor filling in each zone_t with the relevant information and theallocation of the mem_map array for the node. Note that informationon what pages are free for the zones is not determined at this point. Thatinformation is not known until the boot memory allocator is being retired whichwill be discussed much later in Chapter 5.

The core function free_area_init_core() allocates a locallmem_map for the node being initialised. The memory for the array isallocated from the boot memory allocator with alloc_bootmem_node()(see Chapter 5). With UMA architectures,this newly allocated memory becomes the global mem_map but it isslightly different for NUMA.

MAX_NR_ZONES is the maximum number of zones that canbe in a node, i.e. 3. MAX_NR_NODES is the maximum numberof nodes that may exist. The function EXPORT_SYMBOL() makeszone_table accessible to loadable modules. This table is treatedlike a multi-dimensional array. During free_area_init_core(),all the pages in a node are initialised. First it sets the value for the table

As the addresses space usable by the kernel (ZONE_NORMAL) is limited insize, the kernel has support for the concept of High Memory. Two thresholds ofhigh memory exist on 32-bit x86 systems, one at 4GiB and a second at 64GiB. The4GiB limit is related to the amount of memory that may be addressed by a32-bit physical address. To access memory between the range of 1GiB and 4GiB,the kernel temporarily maps pages from high memory into ZONE_NORMALwith kmap(). This is discussed further in Chapter 9.

The second limit at 64GiB is related to Physical Address Extension(PAE) which is an Intel invention to allow more RAM to be used with 32bit systems. It makes 4 extra bits available for the addressing of memory,allowing up to 236 bytes (64GiB) of memory to be addressed.

Secondly, PAE does not allow the kernel itself to have this much RAMavailable. The struct page used to describe each page framestill requires 44 bytes and this uses kernel virtual address space inZONE_NORMAL. That means that to describe 1GiB of memory, approximately11MiB of kernel memory is required. Thus, with 16GiB, 176MiB of memoryis consumed, putting significant pressure on ZONE_NORMAL. This doesnot sound too bad until other structures are taken into account which useZONE_NORMAL. Even very small structures such as Page TableEntries (PTEs) require about 16MiB in the worst case. This makes 16GiB aboutthe practical limit for available physical memory Linux on an x86. If morememory needs to be accessed, the advice given is simple and straightforward,buy a 64 bit machine.

At first glance, there has not been many changes made to howmemory is described but the seemingly minor changes are wide reaching. The nodedescriptor pg_data_t has a few new fields which are as follows:

Even at first glance, zones look very different. Theyare no longer called zone_t but instead referred to as simplystruct zone. The second major difference is the LRU lists.As we'll see in Chapter 10, kernel 2.4 hasa global list of pages that determine the order pages are freed or pagedout. These lists are now stored in the struct zone. The relevantfields are: 2351a5e196