If -Xmx is passed, the JVM will ignore -XX:MaxRAMPercentage (respectively, if -Xms is passed, the JVM will ignore . Your advice is also wrong and detrimental. Xmx 是指设定程序运行期间最大可占用的内存大小。. 0_65"，Java HotSpot(TM) Client VM，Client VM要比Server VM的默认值小. I am not sure if there is any real. jar My initial java version. This means that your JVM will be started with Xms amount of memory and will be able to use a maximum of Xmx amount of memory. Alternatively you can try to switch to G1 garbage collector using -XX:+UseG1GC. The -Xmx option can be used with all OpenJ9 GC policies. Nature's Compass - A utility item that allows you to search for any biome's location in the world. java -Xmx 4g -Xms 1g -jar server. it all depends on the RAM size, you can extend it max upto RAM size. RAM is one of the most necessary resources for the FPS boost. Minimum java heap size. -1. There are a lot of complicated arguments listed in there but the two to adjust are -Xmx {nn} and -Xms {nn} (-Xmn on Mac's). Each thread in a Java application has its own stack. Format for specifying xms: java -xms{Numerical Size}{Unit} where Unit is k/K for kilobytes, m/M for megabytes, and g/G for gigabytes. The -Xms Jvm Arguement allocates a certain amount of RAM on the startup of the laucher, -Xmx sets up a maximum amount that is allowed. Each double argument may have a custom minimum and maximum value. WilsonXRS. Half the available memory with a minimum of 16 MB and a maximum of 512 MB. 3. -XX:NewSize and -XX:MaxNewSize should be set to 25% and 50% of -Xmx for CMS respectively. Syntax. チューニングに関連していると思われるフラグのみ抽出. Xmn、Xms、Xmx、Xss都是JVM对内存的配置参数，我们可以根据不同需要区修改这些参数，以达到运行程序的最好效果。. for example, you can set the java heap size to 258MB by executing following command java -Xmx256m HelloWorld. 32位系统 下，一般限制在1. If the scavenger is disabled, -Xms ≥ -Xmo. -Xmn is an allocated space that the Java GC passes often. Both options take a size. On Windows, use the following command to find out the defaults. In order to allocate more RAM, the launcher needs to be accessed. #5 Expo, Apr 24, 2014. native_memory command. Anything after the . The Java heap can never grow larger than -Xmx. -Xms 3670k-Xmx 64m. Instead of 200, it may use 300. Xmn คือขนาดฮีปสำหรับพื้นที่ฮีปรุ่นใหม่ ออบเจ็กต์ใหม่ถูกสร้างขึ้นในฮีปนี้ Garbage Collector สแกนคนรุ่นใหม่บ่อยมาก. 0 (Squeeze) Minimal (64Bit) with a ligwebserver with php/mySQL alongside the actual Minecraft server. pointless to use. Also, the -Xms value can be used as “minimum heap size” to set a fixed heap size by setting -Xms = -Xmx when, for example, you want to run benchmark tests. The heap size for young generation heap space is Xmn. What you are setting with those values are the minimum startup heap (Xms) and the maximum heap size (Xmx). The modified JVM settings:JVM调优总结 -Xms -Xmx -Xmn -Xss (转) Xms 是指设定程序启动时占用内存大小。. You might want to ensure that you're using: java -Xmx1024m -jar YourApplication. Note: The -Xmo option is not supported by the balanced garbage collection policy. Podéis saber más en la. 提供更好的垃圾回收性能 ：将-Xms和. -Xms ~ -Xmx 값으로 되는 건가 싶네. At initialization of the virtual machine, the entire space for the heap is reserved. and testing -Xmx and -Xmn $ . If -Xmx is passed, the JVM will ignore -XX:MaxRAMPercentage (respectively, if -Xms is passed, the JVM will ignore . -Xms<heap size>[unit] -Xmx<heap size>[unit] Here, unit denotes the unit in which we’ll initialize the memory (indicated by heap size). server. JVM Options Overview. JVM Tuning Summary-XMS-XMX-XMN-XSS Time of Update: 2015-01-26 However, when the heap space is small, after a period of time, "fragmentation" occurs, if the concurrent collector does not find enough space, then the concurrent collector will stop, and then use the traditional token, purging method for recycling. -Xms<size>. defaultAction openFile -. 7. For example;As taken from @dmitripivkine testing, setting -Xmx and -Xmnx $ . -Xmx specifies maximum memory size for Java virtual machine (JVM), while -Xms specifies the initial memory size. 第二个线程在Heap不足时,遍历Heap,将Young 区升级为Older区. -XX:MaxPermSize: Sets the maximum size of the perm memory area. Older区的大小等于-Xmx减去-Xmn,不能将-Xms的值设的过大,因为第二个线程被迫运行会降低JVM的性能. Assuming that you've downloaded and installed Tomcat as Windows Service Installer exe file from the Tomcat homepage, then check the Apache feather icon in the systray (or when absent, run Monitor. jar [arguments] [options] are passed to the Java runtime environment. 1/4th of the physical memory or 1GB. This documentation page on the command line arguments says the following applies to all the arguments accepting memory sizes:Semana passada visitei a casa da minha vó e tentei jogar minecraft no pc de lá. The Java heap can never grow larger than -Xmx. jasotufy2. tldr; what is the theoretical best setup for a Minecraft server where the host has 32 gb of ram and an i9-9900kヒープサイズを固定する場合は、-Xms と -Xmx に同じ値を設定します。 ヒープサイズが拡大または縮小されると、JVM では、事前に定義された NewRatio を維持するために、古い世代と新しい世代のサイズが再計算されます。If I understood correctly, you set the -Xmx on Eclipse launcher. The Java/JVM Xms and Xmx settings should both pre-allocate the amount of memory to start along with the maximum defined value to designate to the Java/JVM instance. Xmn 是指. 以 -X 开头的参数是和实现有关的，并不是适用于所有的 VMs，对于 -Xms 和 -Xmx 其含义为：. 第二个线程在Heap不足时,遍历Heap,将Young 区升级为Older区. -Xms: Sets the minimum and initial size of the heap. Setting Heap Size. Format for specifying xms: java -xms {Numerical Size} {Unit. This. Create a text document in your server folder. During the garbage collection objects that are no longer used are cleared, thus making space for new objects. -Xgcpolicy:gencon. Related javadoc here. Oh, i'm well aware that you totally know what you're doing, but it's more or less aimed at the general public, things like "-XX:+UseConcMarkSweepGC" can actually make the application run a lot slower. -Xms：minimum memory size for pile and heap. d/ directory. The -Xms Jvm Arguement allocates a certain amount of RAM on the startup of the laucher, -Xmx sets up a maximum amount that is allowed. -XX:PermSize: Sets the initial size of the Permanent Generation (perm) memory area. The Java heap can never grow larger than -Xmx . Say you have configured -Xmx value to be 2GB, then configure container’s memory size at least to be. 5、常见配置汇总. java -Xms512m -Xmx2048m -jar craftbukkit. However, the -Xms option can be used with all GC policies except for the metronome GC policy because the heap is always fully expanded. 0. answered Aug 25, 2015 at 13:36. 0. envelope. java -XX:+PrintFlagsFinal -version | findstr HeapSize. Press 'Save Profile' & Press play. Why does setting the -Xmx too high sometimes cause the JVM to fail, even if there's available RAM? 0. . Live & ExclusiveMore than a PlaylistA-List Artists & Hosts. Xms basically means "use at least this amount of ram" and Xmx means "this is your maximum goto ram". Options. If the value of the -Xms parameter is smaller than the value of the -Xmx parameter, than not all of the space that is reserved is immediately committed to the virtual machine. alla then ktlv gi ayto m dhmiourgithike to pa. About xmx. The -Xmx parameter belongs to the (nonstandard) JVM options, and--being an option--needs. Instead this parameter overrides the actual amount of physical RAM when calculating the heap limits basing on ergonomics. Half the available memory with a minimum of 16 MB and a maximum of 512 MB. 5G~2G;64为操作系统对内存无特定限制. Where it says "JVM Arguments" (at the bottom) type in: "-Xmx [amount of memory in GB]G -Xms [same amount of memory in GB]G". 一般来讲，大点，程序会启动的快一点，但是也可能会导致机器暂时间变慢。. アプリケーションがうまく動作するために必要なヒープ領域がわかっている場合は、-Xmsと-Xmxを同じ値に設定できます。 そうでない場合は、JVMが初期ヒープ・サイズを使用して開始され、ヒープ使用量とパフォーマンスのバランスが取れるまで、Javaヒープが. Maximum java heap size. If you want to add a MAX amount of RAM Change -Xmx1G to -Xmx and then the number of ram you want and then the unit, so for 512 MB do -Xmx512M and for 8 GB do -Xmx8G. NOT AN OFFICIAL MINECRAFT. Note: -Xms does not limit the total amount of memory that the JVM can use. -Xmx is max memory. Make plenty of memory available to the young generation. -Xmn. Due to PermGen removal some options were removed (like -XX:MaxPermSize ), but options -Xms and -Xmx work in Java 8. Look for "JAVA_OPTIONS" and just delete it. The -Xms option sets the initial and minimum Java heap size. #7 Nov 11, 2014. STEP 4: To allocate RAM to a Minecraft version, move your mouse over the three dots on the right, CLICK and select Edit. BAT file, it is set to 1024MB (1GB). 1. The Garbage Collector will always try to clean up. Why are XMS and XMX the same thing? Setting the xms to the same value as the xmx will avoid heap expansion pauses. 可以利用JVM提供的-Xmn -Xms -Xmx等选项可进行设置。 例如：java -jar -Xmn16m -Xms64m -Xmx128m MyApp. What to set depend on your application and your hardware. -Xmx - is a maximum Java heap size. This would mean that even putting -Xms128M would work fine because it will automatically increase when the server needs more. Xmn. -Xmx is the max value of your Java heap size. Does this mean the garbage collector wont activate until the JVM. forge 1. This argument is used to specify the maximum RAM usage by Minecraft on your system. 6. Adjust Xms and Xmx to your desired RAM amount leaving at least 1GB open for PermGen and CodeCache *note:setting the Heap above 4GB may cause issues with garbage collection. -Xmn Memory used by the garbage collector for destroyed variables so having it high means big collections of garbage, having it low. 0. l2jfree. ・メタスペースの最大値を512MB確保して、それ以上. -Xms and -Xmx simply specifies the range in which the JVM can operate and resize the heap. Xmn should be set to half of the value specified by the Xmx parameter. java -Xmx####M -Xms####M -exe Minecraft_Server . Also if you are using Java 8, no other additionnal args are necessary other than Xmx and Xms. The Java heap (the “heap”) is the part of the memory where blocks of memory are allocated to objects and freed during garbage collection. 7 Step 3: Start Up The Minecraft Launcher. -Xmx. This means that the JVM should start with 14 GB (-Xms) and grow to a maximum of 14 GB (-Xmx) heap RAM usage. We currently have everything set up to stay within our 1GB guaranteed RAM, but it seems as. 如果程序运行需要占用更多的内存，超出了这个设置值. Skip to navigation. For example, you can set the Java heap size to 258 MB by running the following command: java -Xmx256m HelloWord. This page contains a list of all command argument types. So, java -Xmx4G -Xms1G -jar. The amount allocated for the older generation is the value of -Xmx minus the -Xmn. When the JVM starts, it'll allocate -Xms amount of. When using the balanced GC policy without specifying -Xmn or -Xmns, the GC may decide to shrink eden size below its initial size (25% of -Xms) if it determines that doing so will improve GC performance. I am quite sure my server provider doesn't have the best start parameters. -Xms and -Xmx specify the minimum and maximum size of JVM heap. If your program need more memory than the value specified in Xms the JVM will take more memory until the limit specified in Xmx. , -XX:MaxRAMFraction, -XX:MaxRAMPercentage, -Xmx), always make sure you allocate at least 25% more memory to your container (i. My application always logs the maximum amount of RAM it is allowed to use. The Java Heap Size of Java applications can be changed, we use -Xms and -Xmx parameters to control it. -Xms: Sets the minimum and initial size of the heap. When using the balanced GC policy, specifying -Xmn / -Xmns / -Xmnx may affect balanced GC's ability to satisfy -Xgc:targetPausetime. Enables the option to prevent the java command from running a Java application if it uses the endorsed-standards override mechanism or the extension mechanism. client. You can override this default using the -Xmx command-line option. jar --nogui There should be no space between -Xmx and the value, and -Xms and the value, and no double minus before thee nogui argument. This range is set as a percentage by the parameters -XX:MinHeapFreeRatio=-XX:MaxHeapFreeRatio=; and the total size bounded by -Xms-Xmx. Really, the rest of the arguments are used to further control what the JVM is doing when doing something with a server, but for a. Also Java configuration options (command line parameters) can be. Basically, the JVM will allocate whatever you put in -Xms as soon as the JVM starts, then grow as required to -Xmx, once that is reached, it goes garbage collecting (flushing things no longer used). 第二个线程在Heap不足时,遍历Heap,将Young 区升级为Older区. Minimum java heap size. 2) For HOW TO, enter the procedure in steps. JVM参数-Xms和-Xmx的作用. java -Xmx4g -Xms4g. e. 還有10 則留言 收合留言. . It keeps the allocated ram for the server only and stop the OS from using this ram. Minecraft creates a lot of short-lived objects, so it is better to set this to a larger value like 40% of. 系统的可用虚拟内存限制;3. There is only a need for graphics processing if the machine in question is also running a client (i. So thread stack use non-heap memory. -Xms and -Xmx simply specifies the range in which the JVM can operate and resize the heap. The JVM resizes the heap adaptively, meaning it will attempt to find the best heap size for your application. /temp/jdk-11. -XX:MaxGCPauseMillis=200 -XX:ParallelGCThreads=<var> -XX:ConcGCThreads=<var>. 4. It is recommended to reduce your Xmx/Xms by about 1000-1500M to avoid running out of memory or "OOMKiller" hitting your server. Some explanations:If you have a place where you can put the startup flags in directly, you should be able to just use Aikar's flags there including the xmx and xms values, and leave the max heap size empty wherever else. Is the Xmx and xms, Xmx means maximum ram and xms means minimum ram, a good ram, if you have, will be Xmx10G Xms 8G. jvmArguments parameter:. -Xmx = max heap value, used to avoid OOM, but setting too much might cause OOM or chokes your system-Xmx is NOT the maximum memory value Minecraft will use. Instead "free" shows only 1 GB is used and 7 GB is free. You need to use the set of "non standard" options that are passed to the java command. New and used Minecraft Sets & Toys for sale in Victoria, British Columbia on Facebook Marketplace. Linux. If -Xms is set to a low RAM allocation, It will start up with that much RAM, no matter the maximum set by -Xmx. -Xmx Sets the maximum heap size. At least 1 GB of RAM allocated for the server to run ( -Xmn 128M -Xmx 1G ). See the java - the Java application launcher. Nessa seção irei apenas compartilhar para que você possa colar os argumentos e colocar no seu minecraft ou outro jogo. Really, all you need for memory is the Xmx and Xms or Xmn values. and not: java -jar YourApplication. 堆内存相关配置. Don't set that too high. -Xmx is the maximum of RAM wich Minecraft can allocate. -Xms<size>. 最开始只有 -Xms 的参数，表示 `初始` memory size (m表示memory，s表示size)；. My statement regarding the use of -Xmn and -Xms came from my own experience with the arguments. What is meaning of mx and ms?Note: You can change the amount of memory allocated to your server by changing the values after Xmx and Xms. Syntax. If you click Edit Profile to the left of the Play button, at the bottom of the Profile Editor is a checkbox "JVM Arguments". -Xmx1G will set the MAXIMUM HEAP to 1GB at start-up. 20, The default Java Maximum Heap Size ( Xmx) is changed to be consistent with Java 11, so by default in Java 8, 25% physical memory up to 25GB for the Xmx will be expected. XXMaxPermSize is presumably an argument to the eclipse executable. 1、堆设置-Xms:初始堆大小-Xmx:最大堆大小-XX:NewSize=n:设置年轻代大小-XX:NewRatio=n:设置年轻代和年老代的比值。如:为3，表示年轻代与年老代比值为1：3，年轻代占整个年轻代年老代和的1/4There are two flags to control the heap size: -Xms and -Xmx. Do not set -Xmx / -Xms. -Xmx - This option sets the maximum Java heap size. Download Apache Tomcat. For testing, you can also set the heap sizes using the ES_JAVA_OPTS environment variable:JVM 参数配置及详解 -Xms -Xmx -Xmn -Xss 调优总结. If -Xmx is set, MaxRAM is never used. Advanced Runtime Options. Rather, it specifies the initial heap size (i. Generally, when I need more memory for Minecraft, I set the max heap and not the min heap. The amount allocated for the older generation is the value of -Xmx minus the -Xmn. Go to the “Installations” tab. e. 例如，启动JVM（如下所示）将使用256 MB内存启动，并且允许进程使用最多2048 MB内存：. -Xmssize Specifies the initial heap size. 5GB themselves, totaling a 3gb usage)-Xms = starting free heap value. Error: Could not create the Java Virtual Machine. You can replace that flag with either -Xmx4G or -Xmx4096M to raise this limit to 4GB. This eliminates potentially costly heap reallocations, and can reduce the amount of heap fragmentation that can occur. 1. This only apples to 32 software and by default when yo go to the java site it installs the 32 bit version. Xmx 是指设定程序运行期间最大可占用的内存大小。. Initial heap size is 1/64th of the computer’s physical memory or reasonable minimum based on platform (whichever is larger) by default. epp. Proof: Run the application XX:NativeMemoryTracking=summary and check used memory with jcmd VM. jar nogui" command but it wont work, i get a flash of command prompt and nothing else. minecraft. The uncommitted space is labeled "virtual" in this figure. I have readed that CMSIncrementalMode and Xmn are not usefull, right ? Also, I don't know if I should use -Xms,-XX:ParallelGCThreads, -Dsun. -Xmx<size>. In other words, we allow. 1) For Solution, enter CR with a Workaround if a direct Solution is not available. Use -Xms to specify the initial Java heap size. Hello, Still working on a test install, I am stumbling (and struggling) upon this prerequisite in Step 1 of the Confluence Migrator tool Prerequisites At this step the minimal requirements for the migration are being listed. 物理内存的1/4 (<1GB) 默认 (MaxHeapFreeRatio参数可以调整)空余堆内存大于70%时，JVM会减少堆直到 -Xms的最小限制. Virtual space for a 64 bit CPU is huge. Step-1. eyxaristw. See Using -X command-line options for more information about the <size> parameter. Another option is to set -Xms to the memory-usage value observed at the end of InitServlet. Nota: Lo simplificamos como memoria máxima y mínima aunque es un poco más complejo que esto, tiene que ver con el heap de Java. Xms is the minimum memory to allocate to the program and Xmx is the maximum it is allowed to grow to. Where it says "JVM Arguments" (at the bottom) type in: "-Xmx [amount of memory in GB]G -Xms [same amount of memory in GB]G". Try -Xms16 -Xmx2048m, for instance. Select the one you want to change the amount of RAM for, click on the. If we want to increase the RAM allocation to, say, 2GB, you can simply shut down the server and run it again with increased values: java -Xmx2048M -Xms2048M -jar server. Minimum java heap size. gcInterval=2147483646, -XX:+AlwaysPreTouch, -XX:InitiatingHeapOccupancyPercent, -XX:G1MixedGCLiveThresholdPercent, . -XX:MaxPermSize=size Sets the maximum permanent generation space size. XmnXmsXmxXss有什么区别 Xmn、Xms、Xmx、Xss都是JVM对内存的配置参数，我们可以根据不同需要区修改这些参数，以达到运行程序的最好效果。. 5 Answers. -Xms 堆内存的初始大小，默认为物理内存的1/64 -Xmx 堆内存的最大大小，默认为物理内存的1/4 -Xmn 堆内新生代的大小。. We run Debian 6. The -xmx option is used to set the final and maximum heap size in Java. However, the -Xms option can be used with all GC policies except for the metronome GC policy because the heap is always fully expanded. Figure 4-1 illustrates the difference between committed space and virtual space in the heap. Also, the -Xms value can be used as “minimum heap size” to set a fixed heap size by setting -Xms = -Xmx. Enter in the code to allocate more RAM. -Xmx is the max value of your Java heap size. Set these two parameters to equal values in the MultiMC gui options. The provider had some super long explanation why it was better to still set Xmx to 1G but I was not really buying it and performance increased a lot with setting it to 2G. -Xms : To set an initial java heap size -Xmx : To set maximum java heap size -Xss : To set the Java thread stack size -Xmn : For setting the size of young generation, rest of the space goes for old generation. The maximum theoretical heap limit for the 32-bit JVM is 4G. 在系. Mods, resource packs or view distances above 16 are the only reasons to make it any bigger though. 我在Windows Server 2003 系统，3. -Xms 堆内存 的初始大小，默认为物理内存的1/64. . It is recommended to set it to half of the physical memory. For example, to set the maximum heap size to 2GB, set both Xms and Xmx to 2g: -Xms2g -Xmx2g. That seems very, very specific to me. XXMaxPermSize 1024M -showsplash org. JAR that apparently uses up too much memory, and throws an exception "Java heap space" (or something similar). Where -Xms is the minimum heap size and -Xmx is the maximum heap size. Notes - Provides a clientside in-game notepad. This also leaves room for the. 系统的可用物理内存限制. Click on Your Agent name and click Edit. Closed 3 years ago. Oracle recommends that -Xmn and -Xmx be set to the same value. Xmn sets the size of the new (nursery) heap. g. ago. Hey, i'm having trouble with the java batch file commands, i've tried to run my server using the recommended "java -xmx1024x -xms1024x -jar minecraft_server. 3) For FAQ, keep your answer crisp with examples. All new objects are created into the young generation region (called "eden"). This means that when you start your program the JVM will allocate this amount of memory instantly. Proof: Run the application XX:NativeMemoryTracking=summary and check used memory with jcmd VM. thank you. This option checks if an application is using one of these. . Like Greg says, everything after -vmargs are VM args which are supplied to the JVM when an application starts. Try to increase -Xmx value. Often for client the default value is 1/4th of your physical memory or 1GB (whichever is smaller). Contrary to popular belief, this doesn’t specify a minimum amount of RAM that the JVM will use. platform --launcher. The Xms flag tells to your JVM the amount of memory for initial allocation. When the JVM starts, it'll allocate -Xms amount of virtual memory. UN/LOCODE 2011-2. The options you're looking for are -Xmx and -Xms (this is "initial" heap size, so probably what you're looking for. The short answer is that you use these java command-line parameters to help control the RAM use of application: Use -Xmx to specify the maximum heap size. 4. Also, depending on how you are starting that other app, you may have to specify -Xms for your app instead of the other one. This should not be allowed and a check should be included to prevent this scenario from occurring. Run your server and WOOT! It's fixed :smile. Attachments. Note that -X options are not guaranteed to exist on all VMs or behave the same on all VMs. 0_25, Oracle Corporation Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle CorporationDefault values for JDK 1. -Xms 堆内存的初始大小，默认为物理内存的1/64 -Xmx 堆内存的最大大小，默认为物理内存的1/4 -Xmn 堆内新生代的大小。. thank you man you just helped me alot. If you are monitoring large number of databases, it is recommended to increase the initial (Xms) and maximum (Xmx) heap size values to. edit @Aikar "-Xms matching -Xmx"-Xms is allocated at startup and it will grow up to -Xmx, setting ms == mx effectively turns off this behavior. GameServer REM REM For debug purpose (for devs), use this :. bat EDIT by Moderator: merged posts, please use the edit button instead of double posting. Esto elimina las potencialmente costosas reasignaciones de la pila, y puede reducir la cantidad de fragmentación de la pila que puede ocurrir. Changed flair from help to Tutorial. However, the -Xms option can be used with all GC policies except for the metronome GC policy because the heap is always fully expanded. 7. These options control the runtime behavior of the Java HotSpot VM. When you start multiple java processes, their total memory is not the sum as displayed by top, since they use shared libraries. 举个例子：机器采用4核8G，然后-Xms和-Xmx设置为3G，给整个堆内存3G内存空间，-Xmn设置为2G，给新生代2G内存空间。 而且假设你的业务量如果更大，你可以考虑不只部署3台机器，可以横向扩展部署5台机器，或者10台机器，这样每台机器处理的请求更少，对JVM的压力. The Java heap (the “heap”) is the part of. Updated on October 18, 2021 by Arpit Mandliya. So thread stack use non-heap memory. This increases the size of the permagen space. The thinking that it does something magical for garbage collection. -Xms Java Heap初始值，Server端JVM最好将-Xms和-Xmx设为相同值，开发测试机JVM可以保留默认值； -Xmn Java Heap Young区大小，不熟悉最好保留默认值； -Xss 每个线程的Stack大小，不熟悉最好保留默认值；Minecraft will only ever use one CPU core, even if your machine has multiple cores. For client-side Minecraft, it generally makes sense to set the Xmx and Xms to the same value since the working set is largely uniform, for the entire run, and a resize can add extra time to the GC (depends on how the OS exposes this, really).