ram | 易学教程

i.MX35 suspend CPU and DDR2 from IRAM

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问题 I have to put my device into a very deep low power mode from Linux 2.6.38 and therefore, it's necessary to suspend all components, including CPU und DDR2. What I found out so far is that I have to copy the core assembler function into the processor's internal memory and execute it from there. Basically, it looks like this: cpaddr = iram_alloc(SZ_1K, &iram_addr); if(!cpaddr) return -ENOMEM; suspend_iram_base = __arm_ioremap(iram_addr, SZ_1K, MT_HIGH_VECTORS); memcpy(suspend_iram_base, cpu_v6

Android Available Ram

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问题 How much RAM is available for use by each app? I read somewhere that each app could only use a max of 16 mb, but the total system memory is much higher. 回答1: Each application is limited to 16MB of Java heap space, at least for devices with "normal" class screens. That limit has apparently been bumped to 24MB for devices with "large" class screens -- in part because of larger bitmaps such screens might manipulate, and probably in a trade-off for the minimum amount of device RAM such devices

How does the internal implementation of memcpy work?

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问题 How does the standard C function 'memcpy' work? It has to copy a (large) chunk of RAM to another area in the RAM. Since I know you cannot move straight from RAM to RAM in assembly (with the mov instruction) so I am guessing it uses a CPU register as the intermediate memory when copying? But how does it copy? By blocks (how would it copy by blocks?), by individual bytes (char) or the largest data type they have (copy in long long double's - which is 12 bytes on my system). EDIT: Ok apparently

Need to load the whole postgreSQL database into the RAM

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问题 How do I put my whole PostgreSql database into the RAM for a faster access?? I have 8GB memory and I want to dedicate 2 GB for the DB. I have read about the shared buffers settings but it just caches the most accessed fragment of the database. I needed a solution where the whole DB is put into the RAM and any read would happen from the RAM DB and any write operation would first write into the RAM DB and then the DB on the hard drive.(some thing like the default fsync = on with shared buffers

浅谈RAM、ROM、EPROM、闪存FLASH

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RAM Random Access Memory，随机存取存储器，主要用来储存实时数据，表格等，可以通过指令随机地访问储存单元。它的速度快，但是需要供电才能工作，一旦掉电数据就会丢失。通俗的讲，就类似于手机上的运行内存 ROM Read Only Memory，只读式存储器，通俗的讲，它只支持读，不支持擦写，一般用来存储文件、固定代码和一些固定指令等，不会因掉电而丢失数据。但是写入ROM中的信息只能被读出，不能修改。 EPROM (英文名太长了。)可擦除可编程只读存储器，它是一种可以用特殊的装置擦除或重写其中内容的存储器闪存FLASH 一种非易失性（ Non-Volatile ）内存，就算没有供电它也可以长久的保存数据，可理解为硬盘，支持在线传输，读写速度快来源： CSDN 作者：漠失沉沦链接： https://blog.csdn.net/sinat_39560711/article/details/103578473

what's the difference between working set and commit size?

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问题 when debugging OOM bugs, what's the difference between working set and commit size? Especially what's the exact meaning for commit size? 回答1: From here, the working set is: ... a count of physical memory (RAM) rather than virtual address space. It represents the subset of the process's virtual address space that is valid, meaning that it can be referenced without incurring a page fault. The commit size is: the total amount of pageable virtual address space for which no backing store is

YARN的内存和CPU配置

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时间 2015-06-05 00:00:00 JavaChen's Blog 原文 http://blog.javachen.com/2015/06/05/yarn-memory-and-cpu-configuration.html 主题 YARN Hadoop YARN同时支持内存和CPU两种资源的调度，本文介绍如何配置YARN对内存和CPU的使用。 YARN作为一个资源调度器，应该考虑到集群里面每一台机子的计算资源，然后根据application申请的资源进行分配Container。Container是YARN里面资源分配的基本单位，具有一定的内存以及CPU资源。在YARN集群中，平衡内存、CPU、磁盘的资源的很重要的，根据经验，每两个container使用一块磁盘以及一个CPU核的时候可以使集群的资源得到一个比较好的利用。内存配置关于内存相关的配置可以参考hortonwork公司的文档 Determine HDP Memory Configuration Settings 来配置你的集群。 YARN以及MAPREDUCE所有可用的内存资源应该要除去系统运行需要的以及其他的hadoop的一些程序，总共保留的内存=系统内存+HBASE内存。可以参考下面的表格确定应该保留的内存：每台机子内存系统需要的内存 HBase需要的内存 4GB 1GB 1GB 8GB 2GB

How can I find out the total physical memory (RAM) of my linux box suitable to be parsed by a shell script?

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问题 I'm typing a shell script to find out the total physical memory in some RHEL linux boxes. First of all I want to stress that I'm interested in the total physical memory recognized by kernel, not just the available memory . Therefore, please, avoid answers suggesting to read /proc/meminfo or to use the free , top or sar commands -- In all these cases, their " total memory " values mean " available memory " ones. The first thought was to read the boot kernel messages: Memory: 61861540k

How to delete multiple pandas (python) dataframes from memory to save RAM?

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问题 I have lot of dataframes created as part of preprocessing. Since I have limited 6GB ram, I want to delete all the unnecessary dataframes from RAM to avoid running out of memory when running GRIDSEARCHCV in scikit-learn. 1) Is there a function to list only, all the dataframes currently loaded in memory? I tried dir() but it gives lot of other object other than dataframes. 2) I created a list of dataframes to delete del_df=[Gender_dummies, capsule_trans, col, concat_df_list, coup_CAPSULE

转载： QEMU深入浅出: guest物理内存管理

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作者：Stefan Hajnoczi 领域：Open source and virtualization 适宜读者：对虚拟化有一定了解背景知识：KVM，Qemu 前言：众所周知，内存是计算机系统的一个关键组成部分。使用Qemu-kvm方式创建虚拟机时，guest物理内存是由几个不同层面共同管理的。本篇基于Qemu2.5的代码对管理guest物理内存的这几个重要层面进行概括性的解释，为读者深究Qemu源代码奠定了理论基础。需要注意的是本篇并未涉及guest虚拟内存方面的内容，后续会对其介绍。毕竟使用KVM虚拟化技术的一个重要前提是支持guest与host之间物理内存的转换，并未涉及Qemu中软件模拟的内存管理（即guest虚拟地址与guest物理地址之间的转换）。一、Guest RAM的配置参数 Qemu命令行选项“-m [size=]megs[,slots=n,maxmem=size]”分别定义了guest物理内存的初始化值，内存条（如DIMM）的可用插槽数以及可支持的guest物理内存最大值。有了slot与maxmem这两个参数的定义，在Qemu模拟DIMM热插拔的过程中，guest操作系统像host一样，能够监测到内存块的添加或移除。比如向guest中热插拔一块DIMM内存条，就像是在真实物理机上进行的。再者，guest内存热插拔的操作单位并不是字节

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