Zram stat. Aug 13, 2025 · 前言 最近在折腾几台小内存的VPS�...

Zram stat. Aug 13, 2025 · 前言 最近在折腾几台小内存的VPS，发现内存经常不够用，交换分区又会拖慢系统性能。偶然发现了ZRAM这个好东西，可以在内存中创建压缩的交换空间，既能缓解内存压力，又不会有传统swap的IO瓶颈。今天就来分享一下如何在Linux服务器上配置ZRAM。 什么是ZRAM ZRAM（压缩RAM）是Linux内核的一个模块，它 Sep 20, 2023 · 2. 04 LTSの場合での話)。 zramctlコマンドを使う $ cat /sys/block/zram0/mm_stat 266240 11081 98304 0 98304 2 0 $ zramctl NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STRE… Sep 1, 2025 · I was wrong! zswap IS better than zram September 1, 2025 by Hayden James, in Blog Linux Rule of thumb / TL;DR: If your system only uses swap occasionally and keeping swap demand within ~20–30% of your physical RAM as zram is enough, ZRAM is the simpler and more effective option. For each algorithm I calculated how long time it would take to compress and decompress that amount of data. It covers common tasks, monitoring procedures, and operational workflows. It consists of a single line of text and contains the following stats separated by whitespace: However, with zRam or swap on ramdisk, the kernel is able to move pages to swap and relocate during swapin. Follow this step-by-step guide to boost memory efficiency and responsiveness without hardware upgrades. 6 days ago · Troubleshooting Relevant source files This page provides solutions to common issues encountered when configuring and operating the rpi-swap system. Unit: bytes The zram module creates RAM-based block devices named /dev/zram<id> (<id> = 0, 1, ). Sep 12, 2025 · 内存节省量： original_size - compressed_size，实际释放的内存空间 I/O操作延迟：zram设备的读写延迟，理想情况下应远低于磁盘Swap 这些指标的计算逻辑主要在zram_stats. This excludes same-element-filled pages (same_pages) since no memory is allocated for them. zRAM is a compressed swap device that resides solely in RAM and does not require a backing swap device (i. Mar 20, 2022 · 结合 zramctl 和 mm_stat 的输出，不难发现我们配置的 ZRAM 大小其实是未压缩的大小，而非是压缩后的大小，前面我们提到了一个算法，当 ZRAM 大小为 30GB 且压缩率为 2:1 时，可以获得 60G - (30G / 2) + 30G > 75G 的可用内存，这就是假设了 30GB 的未压缩数据可以压缩到 15G Mar 10, 2026 · zswap is a kernel feature that provides a compressed RAM cache for swap pages. Thus, the allocator is supposed to work well under low memory conditions. After the page has been decompressed into the swap Sep 28, 2022 · ZSwap operates as a compressed RAM cache and works in conjunction with an uncompressed standard swap device described above. conf. 技术背景 说到压缩这个词，我们并不陌生，应该都能想到是降低占用空间，使同样的空间可以存放更多的东西，类似于我们平时常用的文件压缩,内存压缩同样也是为了节省内存。 尽管当前android手机6GB，8GB甚至 Sep 12, 2025 · 最佳实践总结 合理设置zram大小：通常为物理内存的50-100% 选择合适的压缩算法：平衡速度和压缩比 监控关键指标：定期检查 mm_stat 和 io_stat 启用写回功能：处理不可压缩数据和冷数据 定期优化：利用重新压缩功能提高压缩效率 Dec 10, 2019 · Early versions of Raspbian used zram based swap (compressed memory), which by default took a 100 MB chunk of the 512 MB model 1 RAM. 14 引入的zRAM，其原理是实现一个基于RAM的块设备，将那些暂时不用的内存数据进行压缩后存储在这个设备上。 zRAM机制是在低内存下工作，而其自身又要分配内存。 Aug 13, 2025 · 前言 最近在折腾几台小内存的VPS，发现内存经常不够用，交换分区又会拖慢系统性能。偶然发现了ZRAM这个好东西，可以在内存中创建压缩的交换空间，既能缓解内存压力，又不会有传统swap的IO瓶颈。今天就来分享一下如何在Linux服务器上配置ZRAM。 什么是ZRAM ZRAM（压缩RAM）是Linux内核的一个模块，它 文章浏览阅读758次。本文介绍了Linux下使用zram的流程。首先加载zram模块，接着阐述块设备驱动的一般流程，包括注册、申请、初始化队列等步骤。还详细说明了zram_init、zram_add等环节，以及zram设备挂载为swap设备的操作，最后提及可通过相关节点获取zram使用信息。 ZRAM is a kernel module which creates a thinly-provisioned layer over RAM that serves as a compressed swap device that lives only in memory. Z-RAM was developed between 2002 and 2010 by a now-defunct [1] company named Innovative Silicon. ZRAM stops either when re-compression was successful (re-compressed object is smaller in size than the original one) and matches re-compression criteria (e. However, I haven't wrapped my head around its configuration yet or if it's really applicable; the traditional behaviour of zram is that it operates very poorly when it fills and disk-based swap starts being used. Even when assuming that zstd only achieves a conservative 1:2 compression ratio (real world data Apr 9, 2018 · 199 200 File /sys/block/zram<id>/mm_stat 201 202 The stat file represents device's mm statistics. What I have noticed is, dphys-swapfile does not seem to increase the swapfile size it is managing. File /sys/block/zram/mm_stat The stat file represents device’s mm statistics. 205 This excludes same-element-filled pages (same_pages) since Jan 1, 2021 · The updated value can be checked by reading /sys/block/zramX/mm_stat. d/` to override defa File /sys/block/zram<id>/mm_stat The stat file represents device's mm statistics. The device does not consume any memory by default, instead gradually growing and shrinking as it compresses and frees memory. Enhanced Performance and Responsiveness The primary benefit is a significant boost in system performance. After the page has been decompressed into the swap I then dumped swap with dd and used that representative dump to test the compression ratio. 14. What: /sys/block/zram<id>/bd_stat Date: November 2018 Contact: Minchan Kim <minchan@kernel. For automatically entering sleep state on power buttons, menu clicks, or laptop lid events, refer to Power management#ACPI events. a RAM disk with on-the-fly disk compression. That's only my theory, though. You can configure multiple zram devices 6 days ago · Zram Statistics and Performance Metrics When using zram or zram+file mechanisms, detailed compression and performance statistics are available through the sysfs interface at /sys/block/zram0/: 6 days ago · User Guide Relevant source files This guide provides practical information for end users installing, configuring, and managing swap on Raspberry Pi systems using rpi-swap. These algorithms take raw data, analyze patterns within it, and encode it in a more compact form. It consists of a single line of text and contains the following stats May 2, 2025 · ZRAM, on the other hand, operates within RAM, allowing data access hundreds of times faster than disk swap with only microsecond-level latency. In particular, it never attempts higher order page allocation which is very likely to fail under memory pressure. It consists of a single line of text and contains the following stats separated by whitespace: Mar 10, 2026 · zswap is a kernel feature that provides a compressed RAM cache for swap pages. For deep technical implementation details, see Technical Reference. Compression happens in parallel, with one compression stream per core. To test compression time I used statistics of the total amount of data read and written to swap I had collected over a few years. It consists of a single line of text and contains the following stats separated by whitespace: File /sys/block/zram<id>/mm_stat The stat file represents device's mm statistics. Some of the usecases include /tmp storage, use as swap disks, various caches under /var and maybe many more :) Statistics for zsmalloc ¶ 这个分配器是为与zram一起使用而设计的。 因此，该分配器应该在低内存条件下工作良好。 特别是， 它从未尝试过higher order页面的分配，这在内存压力下很可能会失败。 初めに 久しぶりに Fedora (fedora 33) を触ったところ、swap が swap-on-zram という見慣れない形式に変わっていたので zram について調べてみました サマリー メモリ上にブロックデバイスを構成し、そこに書き込むデータを圧縮するこ Swapped: a dirty page can be written to the swap file on disk (on most Linux desktop distributions) or compressed (on Android and CrOS through ZRAM). What: /sys/block/zram<id>/io_stat Date: August 2015 Contact: Sergey Senozhatsky <sergey. It consists of a single line of text and contains the following stats separated by whitespace: Initially the created zram block device does not reserve or use any RAM. Aug 15, 2025 · Unveiling the Power of ZRAM: Key Benefits and Advantages ZRAM delivers several compelling advantages that make it a valuable addition to any Ubuntu system, particularly those with limited RAM. org> Description: The bd_stat file is read-only and represents backing device's statistics (bd_count, bd_reads, bd_writes) in a format similar to block layer statistics file format. As shown in Figure 1, ZRAM compresses the inactive virtual pages and transfers them to the physical memory, which can free a lot of physical memory. This compression happens in real-time, storing data in memory rather than on disk. In 6. Jan 1, 2021 · 前回記事log2ramでzramという便利機能がありました。 興味が出てきたので、ユーザーが指定可能なパラメーターを調べてみます。 log2ramはこちら。 Zram is a Linux kernel module that creates a swap space in RAM as opposed to having it on your disk. Pages written to these disks are compressed and stored in memory itself. For detailed configuration file syntax and options, see Configuration. Introduction ¶ The zram module creates RAM based block devices named /dev/zram<id> (<id> = 0, 1, …). zsmalloc ¶ This allocator is designed for use with zram. I remember in the days of MS-DOS you could use a “RAM doubler” to compress your memory storage and get “more” RAM, and then a bit later on there was a joke website where you could “download” more RAM. " This page updates in real-time to show how your Chromebook is running. 2. When I check the statistics with cat /sys/block/zram0/mm_stat, the value mem_used_max is a bit higher than the TOTAL value (but far below DATA). The block device created with zram can then be used for swap or as a general-purpose RAM disk. It works like MS Windows’ “virtual memory”, that uses the hard disk for additional memory when there is not enough physical RAM for all tasks request. This was not a good choice, in my opinion, whereas the dphys-swapfile thing seems sensible enough. Some of the use cases include /tmp storage, use as swap disks, various caches under /var and maybe many more. Oct 8, 2023 · 一文彻底理解Memory barrier（内存屏障） 一篇文带你搞懂，虚拟内存、内存分页、分段、段页式内存管理（超详细） 在 Linux-3. Here is the whole tutorial about zRam in Ubuntu: zRam is a code inside kernel, that once activated, creates a RAM based block device which acts as a swap disk, but is compressed and stored in memory, allowing very fast I/O and increasing the amount of memory available before the system starts swapping to disk. It is a module of the Linux kernel since 3. :) Statistics for individual zram 目前， comp_algorithm 内容仅显示 zram 支持的压缩算法。 3) 设置压缩算法参数：可选 ¶ 压缩算法可能支持特定的参数，可以针对特定的数据集进行调整。 ZRAM 有一个 algorithm_params 设备属性，它提供每个算法的参数配置。 例如，几种压缩算法支持 level 参数。此外，某些压缩算法支持预训练的字典，这会 0 0 0 652572 -- zram<id>/mm_stat accumulates zram mm stats and contains: orig_data_size compr_data_size mem_used_total mem_limit mem_used_max zero_pages num_migrated Example: cat /sys/block/zram0/mm_stat 434634752 270288572 279158784 0 579895296 15060 0 per-stat sysfs nodes are now considered to be deprecated and we plan The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. Optimize your low-RAM VPS with ZRAM for enhanced performance. 概述zsmalloc是Seth Jenningsd 为内存压缩zram实现的一种内存分配器。已经有了slab， 为何还需要zsmalloc？ 在内核中，slab分配器用于分配较小块内存，它将多个相同大小的对象放在同一个内存页中，但这些对象可… Mar 17, 2021 · Take advantage of compressed RAM based block devices to create temporary filesystems and swap disks. This is particularly useful for memory constrained systems. e. Aug 22, 2024 · Zram Performance Analysis Introduction Zram is a kernel module that utilizes a compressed virtual memory block device allowing for efficient memory management. Because zram can transparently compress data, it may be used as a swapfile which effectively allows RAM to be compressed as it is paged out. zRam is integrated into the Linux kernel 3. Pages which would otherwise be swapped out to disk are instead compressed and stored into a memory pool in RAM. Swap partition/files on an HDD/SSD are very slow and often results in stuttering when the machine decides to start using the swap space. ” When the system needs to access the data, it decompresses it back to its original form. The module has been part of the mainline kernel since version 3. It consists of a single line of text and contains the following stats separated by whitespace: Jun 24, 2020 · I can see that zram definitely helps to get more out of available RAM, despite that these DATA values appear to contradict each other. g. conf 6 days ago · This page provides practical configuration examples for common rpi-swap use cases. Users may create a swap space during installation or at any later time as desired. The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. 10，main或master分支不维护请勿使用） - zhgding/istoreos_istoreos zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i. The choice of compression Jul 12, 2025 · Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and more. Once the pool is full or the RAM is exhausted, the least recently used (LRU) page is decompressed and written to disk, as if it had not been intercepted. The page will stay swapped until a new page fault on its virtual address happens, at which point the kernel will bring it back in main memory. 3. It consists of a single line of text and contains the following stats separated by whitespace: ABI file testing/sysfs-class-zram ¶ Has the following ABI: /sys/class/zram-control/ /sys/class/zram-control/hot_add /sys/class/zram-control/hot_remove ABI file testing/sysfs-dev ¶ Has the following ABI: /sys/dev ABI file testing/sysfs-devices ¶ Has the following ABI: /sys/devices ABI file testing/sysfs-devices-consumer ¶ Has the following ABI: Jun 24, 2020 · I can see that zram definitely helps to get more out of available RAM, despite that these DATA values appear to contradict each other. It is only recommended for tight disk spaces /embedded systems where regular swap partition does not make sense. Jan 30, 2025 · ZRAM relies on compression algorithms to reduce the size of data stored in memory. Nov 18, 2023 · zram is a Linux kernel module that creates a RAM backed block device with features including on-the-fly compression. Swap on disk Sep 26, 2020 · 问题描述 我们可以通过 cat /sys/block/zram0/mm_stat 来查看某个ZRAM区块的使用情况 这条命令运行后会得到这样一组数据 1007837184 266412961 281042944 0 392597504 28298 1341647 16923 0 0 按照Linux内核官方文档，这组数据的含义是 The stat file represents device's mm statistics. uncompressed swap space on a hard drive or SSD). Z-RAM is a tradename of a now-obsolete dynamic random-access memory technology that did not require a capacitor to maintain its state. The zram block device will then dynamically grow or shrink as required. 1 (stable in Debian), zram's data stat matched swapon's stat (which is the same as the swap stat in free, top, etc). It consists of a single line of text and contains the following stats separated by whitespace: Aug 28, 2024 · This is a step by step tutorial shows how to enable zram Kernel module and use as Swap device for better system performance in Ubuntu 24. Unit: bytes The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. senozhatsky@gmail. Zram is an alternative to a disk swap space that compresses memory before storing it in a designated space Nov 11, 2022 · Zram is a tool for creating an in-RAM compressed cache, specifically for use as swap space. For configuration syntax and options, see swap. For general monitoring and status checking procedures, see Monitoring and Status. Jul 7, 2024 · In 6. Z-RAM relies on the floating body effect, [2] an artifact of the silicon on insulator (SOI) process which places transistors in isolated tubs (the transistor body . See Linux zram documentation and Zram for more info. Linux systems use zram primarily for swap space and temporary file storage. File format is similar to block layer statistics file format. On the other hand, if we just use single (0-order) pages, it would suffer from very high fragmentation -- any object of size PAGE_SIZE/2 or larger Zram actually harms system performance as it allocates static space on ram and wastes cpu time trying to compress data regardless of it is compressable or not. This greatly helps maintain system responsiveness even in low-memory situations. Whether or not it is beneficial to extend the virtual memory with swap depends on the amount of May 31, 2018 · もしかしたら環境によっては入っていないかもしれない (以下はUbuntu 18. 04 PC/laptop with limited RAM. On the other hand, if we just use single (0-order) pages, it would suffer from very high fragmentation -- any object of size PAGE_SIZE/2 or larger Mar 2, 2026 · Note The goal of the high level interface is to provide binaries/scripts that can be invoked to perform suspend/hibernate and ways to hook extra preparatory/cleanup work into the said process. Only as files need or want to be swapped out, they will be compressed and moved into the zram block device. On the other hand, if we just use single (0-order) pages, it would suffer from very high fragmentation -- any object of size PAGE_SIZE/2 or larger Sep 26, 2020 · 问题描述 我们可以通过 cat /sys/block/zram0/mm_stat 来查看某个ZRAM区块的使用情况 这条命令运行后会得到这样一组数据 1007837184 266412961 281042944 0 392597504 28298 1341647 16923 0 0 按照Linux内核官方文档，这组数据的含义是 The stat file represents device's mm statistics. Well both of these are a reality in Linux (no joke), called Zram On my test system, the Odroid-m1, without zram - I have 8GB of physical RAM, and no swap: zram (previously called compcache) can create RAM based compressed block devices. ZRAM Memory Compression System We revisit a popular Linux kernel software memory compression subsystem, namely the ZRAM module. 12, they differ. It consists of a single line of text and contains the following stats separated by whitespace: Jun 7, 2020 · 每当重置zram时，写回限制计数将重置（例如，系统重新启动，echo 1>/sys /block /zramX /reset）， 保证写回次数直到重新设置zram分配的写回预算，是用户的工作。 如果管理员想在某个时间段内测量写回计数，他可以通过 /sys /block /zram0 /bd_stat的第 3列了解它。 Mar 20, 2022 · 结合 zramctl 和 mm_stat 的输出，不难发现我们配置的 ZRAM 大小其实是未压缩的大小，而非是压缩后的大小，前面我们提到了一个算法，当 ZRAM 大小为 30GB 且压缩率为 2:1 时，可以获得 60G - (30G / 2) + 30G > 75G 的可用内存，这就是假设了 30GB 的未压缩数据可以压缩到 15G However, with zRam or swap on ramdisk, the kernel is able to move pages to swap and relocate during swapin. The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. But if swap use regularly pushes far beyond that, is unpredictable, or if your system has fast storage (NVMe Mar 8, 2020 · zRAM内存压缩技术原理与应用 作者： OPPO内核团队 发布于：2020-3-8 8:38 分类： 内存管理 1. :) Statistics for Apr 25, 2025 · Allocate compressed swap space in RAM with Zram to improve Linux system responsiveness and reduce reliance on slow disk swap, especially on devices with limited memory. If physical swap devices exist, they will also be used by the system, but with a lower priority than a Zram device. Aug 14, 2017 · what is zram? Zram wiki zram zram（也称为 zRAM，先前称为 compcache）是 Linux 内核的一项功能，可提供虚拟内存压缩。zram 通过在 RAM 内的压缩块设备上分页，直到必须使用硬盘上的交换空间，以避免在磁盘上进行分页，从而提高性能。由于 zram 可以用内存替代硬盘为系统提供交换空间的功能，zram 可以在需要 May 2, 2025 · ZRAM, on the other hand, operates within RAM, allowing data access hundreds of times faster than disk swap with only microsecond-level latency. ) TL;DR: zRam in a system without real swap space allows kernel to use all swap related codepaths which may avoid some bugs. For example, failed_reads, failed_writes, etc. It consists of a single line of text and contains the following stats 提供一个人人会用的的路由、NAS系统 （目前活跃的分支是 istoreos-24. Feb 12, 2016 · Here you go. Jan 17, 2026 · Swap space can take the form of a disk partition or a file. It consists of a single line of text and contains the following stats separated by whitespace: zram block device … zram compressor zram的compressor在每个cpu有独立stream object，每个核可以独立并行处理压缩过程。 zram的压缩算法定义在zcomp的显式list中，除了这个静态压缩算法列表，仍然可以设置crypto中存在的其他算法。 write back CONFIG_ZRAM_WRITEBACK Sep 21, 2020 · This opens the "System Internals" overview page. It consists of a single 203 line of text and contains the following stats separated by whitespace: 204 orig_data_size uncompressed size of data stored in this disk. It consists of a single line of text and contains the following stats separated by whitespace: orig_data_size uncompressed size of data stored in this disk. Mar 17, 2021 · Take advantage of compressed RAM based block devices to create temporary filesystems and swap disks. Each example demonstrates how to configure the system using drop-in files in `/etc/rpi/swap. 2 and above, so it's Zram actually harms system performance as it allocates static space on ram and wastes cpu time trying to compress data regardless of it is compressable or not. I then dumped swap with dd and used that representative dump to test the compression ratio. As you may know, Ubuntu usually includes a swap space. 0 0 0 652572 -- zram<id>/mm_stat accumulates zram mm stats and contains: orig_data_size compr_data_size mem_used_total mem_limit mem_used_max zero_pages num_migrated Example: cat /sys/block/zram0/mm_stat 434634752 270288572 279158784 0 579895296 15060 0 per-stat sysfs nodes are now considered to be deprecated and we plan Jan 21, 2026 · The zram module creates compressed block devices in RAM. It covers configuration change problems, swap activation failures, writeback issues, and diagnostic procedures. These disks allow very fast I/O and compression provides good amounts of memory savings. The amount they differ is variable and unpredictable, suggesting the discrepancy is somehow related to the nature of the data itself. It consists of a single line of text and contains the following stats separated by whitespace: – orig_data_size – compr_data_size – mem_used_total – mem_limit – mem_used_max – zero_pages Nov 18, 2023 · zram is a Linux kernel module that creates a RAM backed block device with features including on-the-fly compression. c中实现，通过内核统计框架向用户空间暴露。 监控方案实战 掌握zram监控方法是系统优化的关键。 Jun 8, 2021 · Zram, Kernel,Native Cached+Free的内存代表着当前整个手机的可用内存，如果值很小，意味着处于内存紧张状态。 一般低内存的判定阈值为：4G 内存手机以下阀值：350MB，以上阀值则为：450MB ps:如果ANR时间点前后，日志里有打印onTrimMemory，也可以作为内存紧张的一个参考 Feb 12, 2026 · ZRAM iterates the list of registered alternative compression algorithms in order of their priorities. 14 引入了一种名为 zRAM 的技术，zRAM 的原理是：将进程不常用的内存压缩存储，从而达到节省内存的使用。 如下图所示： Introduction ¶ The zram module creates RAM-based block devices named /dev/zram<id> (<id> = 0, 1, …). On the other hand, if we just use single (0-order) pages, it would suffer from very high fragmentation -- any object of size PAGE_SIZE/2 or larger Apr 14, 2025 · 但是建立在swap机制上的zRAM机制将压缩后的数据存储在内存中，对性能影响较小。 在 Linux-3. These devices compress data automatically when you write to them. There are three columns for "CPU," "Memory," and " Zram. Swap space can be used for two purposes, to extend the virtual memory beyond the installed physical memory (RAM), and also for suspend-to-disk support. 结合 zramctl 和 mm_stat 的输出，不难发现我们配置的 ZRAM 大小其实是未压缩的大小，而非是压缩后的大小，前面我们提到了一个算法，当 ZRAM 大小为 30GB 且压缩率为 2:1 时，可以获得 60G - (30G / 2) + 30G > 75G 的可用内存，这就是假设了 30GB 的未压缩数据可以压缩到 15G zramctl is used to quickly set up zram device parameters, to reset zram devices, and to query the status of used zram devices. 1. I have read the later versions of zram allow it to operate as a writeback cache, which implies it now can do what zswap does. It consists of a single line of text and contains the following stats separated by whitespace: The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. For swapon -s it is the reported uncompressed size for sure. com> Description: The io_stat file is read-only and accumulates device's I/O statistics not accounted by block layer. size threshold) or when there are no secondary algorithms left to try. The compressed data is then stored in a portion of RAM designated as a “compressed block device. 14 引入了一种名为 zRAM 的技术，zRAM 的原理是：将进程不常用的内存压缩存储，从而达到节省内存的使用。 如下图所示： The stat file represents device’s I/O statistics not accounted by block layer and, thus, not available in zram<id>/stat file. xlasau kdcizj xhofp xkxi ceoqa hhnnse dhqjyo ueh xqsyyd uxs