Patent Publication Number: US-2023153171-A1

Title: Memory ballooning related memory allocation techniques for execution environments

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 17/082,654, filed Oct. 28, 2020, entitled “MEMORY BALLOONING RELATED MEMORY ALLOCATION TECHNIQUES FOR VIRTUAL MACHINES” issued as U.S. Pat. No. 11,550,729 on Jan. 10, 2023, the entire content of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure is generally related to virtualized computer systems, and more particularly, to memory ballooning related memory allocation techniques for execution environments. 
     BACKGROUND 
     Virtualization herein shall refer to abstraction of some physical components into logical objects in order to allow running various software modules, for example, multiple operating systems, concurrently and in isolation from other software modules, on one or more interconnected physical computer systems. Virtualization allows, for example, consolidating multiple physical servers into one physical server running multiple virtual machines (also referred to herein as “guests” running on a host computer system) in order to improve the hardware utilization rate. 
     Virtualization may be achieved by running a software layer, often referred to as “hypervisor,” above the hardware and below the virtual machines. A hypervisor may run directly on the server hardware without an operating system beneath it or as an application running under a traditional operating system. A hypervisor may abstract the physical layer and present this abstraction to virtual machines to use, by providing interfaces between the underlying hardware and virtual devices of virtual machines. 
     Processor virtualization may be implemented by the hypervisor scheduling time slots on one or more physical processors for a virtual machine, rather than a virtual machine actually having a dedicated physical processor. Memory virtualization may be implemented by employing a page table (PT) which is a memory structure translating virtual memory addresses to physical memory addresses. Device and input/output (I/O) virtualization involves managing the routing of I/O requests between virtual devices and the shared physical hardware. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of examples, and not by way of limitation, and may be more fully understood with references to the following detailed description when considered in connection with the figures, in which: 
         FIG.  1    depicts a high-level block diagram of an example host computer system that performs memory allocation for execution environments, in accordance with one or more aspects of the present disclosure; 
         FIG.  2    depicts a block diagram illustrating components and modules of an example computer system, in accordance with one or more aspects of the present disclosure; 
         FIG.  3    depicts a flow diagram of an example method for inflating a memory balloon with a set of guest memory within a requested range, in accordance with one or more aspects of the present disclosure; 
         FIG.  4    depicts a block diagram of an example computer system in accordance with one or more aspects of the present disclosure; 
         FIG.  5    depicts a flow diagram of another example method for inflating a memory balloon with a set of guest memory within a requested range, in accordance with one or more aspects of the present disclosure; and 
         FIG.  6    depicts a block diagram of an illustrative computing device operating in accordance with the examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are systems and methods for memory encryption for memory ballooning related memory allocation techniques for execution environments. 
     Memory ballooning is a dynamic memory management technique for execution environments (e.g., virtual machines, containers, applications, etc.) to allow the host system to reclaim unused memory from certain execution environments and allocate the reclaimed memory to other execution environments. In one example, an execution environment may release memory that is no longer being used to the hypervisor. The released memory may be placed in a reserved memory pool called a balloon. The hypervisor may then re-allocate the released memory in the balloon to other execution environments or for use by the hypervisor, host operating system, underlying hardware device, or a combination thereof. The released memory may then be removed from the balloon and returned to the execution environment at a later time. 
     In some systems, the hypervisor may request a size of guest memory (e.g., such as 2 MB, 8 MB, etc., or an amount of memory pages) to be made available to the hypervisor. “Memory page” herein shall refer to a contiguous portion of memory of a certain size. For example, a standard memory page may have the size of 4 KB, while a huge page may have the size of 2 MB or 1 GB. The execution environment may have memory pages that are free or can be freed and, thus, may search for such unused guest memory of the requested size. In some examples, the execution environment may allocate multiple portions of unused guest memory from different locations to satisfy the memory request. However, allocating portions from different locations may degrade performance of the execution environment due to memory fragmentation caused by breaking up contiguous partitions of guest memory, such as huge pages. In another example, the execution environment may break up a contiguous portion of unused guest memory until obtaining the requested size of guest memory. For example, responsive to a memory request of 2 MB, the execution environment may identify an 8 MB contiguous portion of unused guest memory, break up the portion into two 4 MB partitions, break up one of the 4 MB partitions into two 2 MB partitions, and release one of the two 2 MB partitions to the hypervisor. However, allocating large portions of contiguous memory depletes the amount of contiguous free memory available on the execution environment, which also may degrade performance of the execution environment due to memory fragmentation. Fragmentation of the guest memory may lead to performance degradation because the execution environment may not be able to satisfy large, contiguous memory allocation requests from applications. As such, it is desirable to prevent guest memory fragmentation from placing guest memory portions in a reserved memory pool and releasing host memory to the hypervisor (e.g., inflating a memory balloon). 
     Aspects of the present disclosure address the above and other deficiencies by implementing memory ballooning related memory allocation techniques for execution environments. In particular, aspects of the present disclosure provide technology that allows a hypervisor to specify a size range of requested guest memory, and inflate a memory balloon with any sized set of guest memory within the requested range. This allows the hypervisor to minimize fragmentation when inflating the memory balloon increasing the likelihood that the hypervisor may identify a portion of guest memory the exact size of the memory request, rather than allocating multiple portions of unused guest memory or breaking up a contiguous portion of guest memory. In an example, the hypervisor may maintain a list of free (e.g., unused) memory pages for each execution environment (e.g., for one or more containers). The list may be included in a data structure, such as, for example, a table. Each entry in the list may reference a set of memory pages that are contiguous in a guest address space. For example, each entry may be one or more contiguous standard memory pages, one or more contiguous huge pages, or any combination thereof. The operating system of the hypervisor may receive a request, from a management application, for guest memory to be made available to the hypervisor. The request may include a range of the desired size of guest memory. For example, the request may include a minimum size of guest memory requested and a maximum size of guest memory. The operating system may then identify a set of contiguous guest memory in the list of free memory pages that is that is greater than or equal to the minimum size of memory requested, and less than or equal to the maximum size of memory requested. The operating system may then release the set of contiguous guest memory to the hypervisor. The released memory may be placed in a reserved memory pool (e.g., a balloon). 
     In an illustrative example, an execution environment may include entries of 2 MB, 2 MB, 5 MB, and 8 MB of free memory pages. The hypervisor may request a minimum of 4 MB of guest memory, and a maximum of 6 MB of guest memory. In response, the operating system of the hypervisor may query the list of free memory pages, and identify the 5 MB entry. The operating system may then release memory pages associated with the 5 MB entry to the hypervisor. In conventional systems, the hypervisor may have allocated both 2 MB portions, or broken up the 8 MB portion into two 4 MB portions to allocate a 4 MB portion. Both scenarios would have increased memory fragmentation. 
     Various aspects of the above referenced methods and systems are described in details herein below by way of examples, rather than by way of limitation. The examples provided below discuss a virtualized computer system where memory movement may be initiated by aspects of a hypervisor, a host operating system, a virtual machine, or a combination thereof. In other examples, the memory movement may be performed in a non-virtualized computer system that is absent a hypervisor or other virtualization features discussed below. 
       FIG.  1    depicts an illustrative architecture of elements of a computer system  100 , in accordance with an implementation of the present disclosure. It should be noted that other architectures for computer system  100  are possible, and that the implementation of a computing device utilizing implementations of the disclosure are not necessarily limited to the specific architecture depicted. Computer system  100  may be a single host machine or multiple host machines arranged in a cluster and may include a rackmount server, a workstation, a desktop computer, a notebook computer, a tablet computer, a mobile phone, a palm-sized computing device, a personal digital assistant (PDA), etc. In one example, computing device  100  may be a computing device implemented with x86 hardware. In another example, computing device  100  may be a computing device implemented with PowerPC®, SPARC®, or other hardware. In the example shown in  FIG.  1   , computing device  100  may include execution environments  110 A-C, hypervisor  120 , hardware devices  130 , and a network  140 . 
     Hypervisor  120 , also be known as a virtual machine monitor (VMM), may manage the execution of one or more execution environments and provide the execution environments with access to one or more underlying computing devices (e.g., hardware or virtualized resources). Hypervisor  120  may interact with hardware devices  130  and provide hardware virtualization, operating-system virtualization, other virtualization, or a combination thereof. Hardware virtualization may involve the creation of one or more virtual machines that emulate an instance of a physical computing machine. Operating-system-level virtualization may involve the creation of one or more virtual machines that emulate an instance of an operating system. In one example, hypervisor  120  may be part of a non-virtualized operating system that is absent hardware virtualization and operating-system-level virtualization and each of the execution environments  110 A-C may be an application process managed by the non-virtualized operating system. In another example, each of execution environments  110 A-C may be or execute within a separate virtual machine or container. In either example, the hypervisor may be implemented as part of a kernel and execute as one or more processes in kernel space (e.g., privileged mode, kernel mode, root mode). 
     In the example shown, hypervisor  120  may run directly on the hardware of computer system  100  (e.g., bare metal hypervisor). In other examples, hypervisor  120  may run on or within a host operating system (not shown). Hypervisor  120  may manage system resources, including access to hardware devices  130 , and may manage execution of execution environments  110 A-C on a host machine. This includes provisioning resources of a physical central processing unit (“CPU”) to each execution environment  110 A-C running on the host machine. Provisioning the physical CPU resources may include associating one or more vCPUs with each execution environment  110 A-C. VCPUs may be provisioned by a core of the physical host CPU or a number of time slots reserved from one or more cores of the physical host CPU. VCPUs may be implemented by an execution thread that is scheduled to run on a physical host CPU. Software executing in execution environment  110 A-C may operate with reduced privileges such that hypervisor  120  retains control over resources. Hypervisor  120  retains selective control of the processor resources, physical memory, interrupt management, and input/output (“I/O”). 
     Execution environments  110 A-C may include a sequence of instructions that can be executed by one or more processing devices (e.g., physical processing devices  134 ). A execution environment may be managed by hypervisor  120  or may be a part of hypervisor  120 . For example, hypervisor  120  may execute as one or more execution environments that cooperate to manage resources accessed by execution environments  110 A-C. Each execution environment may include one or more processing threads, processes, other stream of executable instructions, or a combination thereof. A processing thread (“thread”) may be the smallest sequence of programmed instructions managed by hypervisor  120 . A process may include one or more threads and may be an instance of an executable computer program. 
     In some implementations, execution environment  110 A-C may be an executable container (hereafter “container”) or run a container. Containers may include application images built from pre-existing application components and source code of users managing the application. An image may refer to data representing executables and files of the application used to deploy functionality for a runtime instance of the application. In one implementation, the image can be built using a Docker™ tool and is referred to as a Docker image. In other implementations, the application images can be built using other types of containerization technologies. An image build system (not pictured) can generate an application image for an application by combining a preexisting ready-to-run application image corresponding to core functional components of the application (e.g., a web framework, database, etc.) with source code specific to the application provided by the user. The resulting application image may be pushed to an image repository (not shown) for subsequent use in launching instances of the application images for execution. 
     In various implementations, a container may be a secure process space on the execution environment  110 A-C to execute functionality of an application. A process space is the volume of memory which is allocated for potential memory addresses related to a computing device. In some implementations, a container is established at execution environment  110 A-C with access to certain resources of the underlying node, including memory and storage. In one implementation, containers may be established using the Linux Containers (LXC) method. In further implementations, containers may also be established using cgroups, SELinux™, and kernel namespaces, to name a few examples. 
     In some implementations, execution environment  110 A-C may execute guest executable code that uses an underlying emulation of physical resources, such as, for example, guest memory  114 A-C. Guest memory  114 A-C may be any virtual memory, logical memory, physical memory, other portion of memory, or a combination thereof for storing, organizing, or accessing data. Guest memory  114 A-C may represent the portion of memory that is designated by hypervisors  120  for use by one or more respective execution environments  110 A-C. Guest memory  114 A-C may be managed by host operating system  125  and may be segmented into guest pages. The guest pages may each include a contiguous or non-contiguous sequence of bytes or bits and may have a page size that is the same or different from a memory page size used by hypervisor  120 . Each of the guest page sizes may be a fixed-size, such as a particular integer value (e.g., 4 KB, 2 MB) or may be a variable-size that varies within a range of integer values. 
     In the example shown in  FIG.  1   , hypervisor  120  may include memory manager  122 , guest operating system  125 , and hypervisor memory  123 . Hypervisor memory  123  (e.g., host memory) may be the same or similar to the guest memory and may be managed by hypervisor  120 . Hypervisor memory  123  may be segmented into host pages, which may be in different states. The states may correspond to unallocated memory, memory allocated to guests, and memory allocated to hypervisor(s). The unallocated memory may be host memory pages and guest memory pages that have not yet been allocated by hypervisor memory  123  or were previously allocated by hypervisor  120  and have since been deallocated (e.g., freed) by hypervisor  120 . The memory allocated to guests may be a portion of hypervisor memory  123  that has been allocated by hypervisor  120  to execution environment  110 A-C and corresponds to guest memory of execution environment  114 A-C. Other portions of hypervisor memory may be allocated for use by hypervisor  120 , host operating system  125 , hardware device, other module, or a combination thereof. Hypervisor memory may include memory balloon  124 , discussed below. 
     Host operating system  125  may include executable code that manages applications, device drivers, execution environments  110 A-C, other executable code, or a combination thereof. Host operating system  125  may include operating systems such as, for example, Microsoft® Windows®, Linux®, Solaris®, etc. may execute operations that manage guest memory  114 A-C, memory balloon  124 , balloon driver  126 , and allocation component  128  respectively. Balloon driver  126  and allocation component  128  are used by way of example, and may be any type of device driver, application, program, etc. 
     Memory manager  122  may be a management application that enables memory balloon operations by allowing hypervisor  120  to obtain and use memory pages from execution environment  110 A-C using, for example, memory balloon  124 , balloon driver  126  and/or allocation component  128 . Memory ballooning generally refers to a method of virtual memory management that allows hypervisor  120  to use memory allocated to any one of execution environment  110 A-C. Memory manager  122  may further track and manage mappings between guest memory  114 A-C and hypervisor memory  123 . For example, memory manager  122  may maintain a table, list or other structure that associates an address of guest memory  114 A-C (e.g., a guest address) with an address of corresponding hypervisor memory  123  (e.g., a host address). 
     Balloon driver  126  may be a computer program installed on host operating system  125  used to perform memory balloon operations involving guest memory  114 A-C. In an example, hypervisor  120  uses balloon driver  126  to perform memory balloon operations involving guest memory  114 A-C. For example, hypervisor  120  may use balloon driver  126  to inflate and deflate memory balloon  124  to reclaim or return guest memory  114 A-C from/to execution environment  110 -C. Balloon driver  126  may be loaded into host operating system  125  as a pseudo-device driver, and may have no external interface to host operating system  125 . Accordingly, balloon driver  126  may not be known to host operating system  125 , and hypervisor  120  may communicate with balloon driver  126  over a private communication channel. In some implementations, a single balloon driver  126  may be used for two or more execution environments  110 A-C. In other implementations, each execution environment  110 A-C may be assigned a respective balloon driver  126 . 
     Memory balloon  124  may be a reserved memory pool inaccessible to execution environment  110 A-C. For example, memory pages that have been placed in memory balloon  124  may be hidden from execution environment  110 A-C, inaccessible to execution environment  110 A-C, or protected from execution environment  110 A-C access. In one example, memory balloon  124  may refer to a classification or status of memory. For example, memory pages removed from guest memory  114 A-C may be tagged with a status (e.g., “reserved,” “unavailable,” etc.) to indicate that corresponding memory pages may not be used by execution environment  110 A-C. In some implementations, a singe memory balloon  124  may be used for two or more execution environments  110 A-C. In other implementations, each execution environment  110 A-C may be assigned a respective memory balloon  124 . 
     In an example, execution environment  110 A-C may have guest memory  114 A-C that is free or can be freed. Memory ballooning allows hypervisor  120  to use memory allocated to execution environment  110 A-C. Hypervisor  120  may borrow memory allocated to execution environment  110 A-C by inflating memory balloon  124 . For example, memory manager  122  may send a memory request to balloon driver  126  over the private communication channel. The memory request may specify a target memory balloon  124  size or size range corresponding to an amount of memory sought by hypervisor  120 . The balloon driver  126  may inflate memory balloon  124  in response to receiving a request for guest memory  114 A-C from memory manager  122 . In some implementations, balloon driver  126  may inflate a memory balloon  124  by pinning memory pages from guest memory  114 A-C in the memory balloon  124 . In some implementations, balloon driver  126  inflates a memory balloon  124  by placing a number of memory pages from guest memory  114 A-C in a reserved area of host operating system  125  associated with memory balloon  124 . For example, the reserved area may be inaccessible to the execution environment  110 A-C and/or may prevent execution environment  110 A-C from performing operations involving memory pages pinned in memory balloon  124 . 
     Allocation component  128  may enable hypervisor  120  to specify a size range of requested guest memory and may enable execution environment  110 A-C to inflate memory balloon  124  with a set of guest memory within the requested range. In particular, allocation component  128  may maintain a list of unused guest memory  114 A-C. For example, allocation component  128  may maintain a list where each entry references a set of free memory pages contiguous in the guest address space. Each entry may be one or more contiguous standard memory pages, one or more contiguous huge pages, or any combination thereof. The list may be included in a data structure, such as, for example, a table. 
     Further, allocation component  128  may receive memory requests from hypervisor  120  via, for example memory manager  122 . Each memory request may include a size range of desired guest memory. In particular, the request may include a minimum size of guest memory requested and a maximum size of guest memory. For example, the memory request may specify a size of guest memory requested (e.g., 2 KB, 5 MB, 1 GB, etc.), an amount of one or more types of memory pages requested (e.g., 12 standard memory pages, 4 huge memory pages, etc.) or any combination thereof. Responsive to the memory request, memory allocation component  128  may identify an entry from the list of a set of unused guest memory that is greater than or equal to the minimum size of memory requested, and less than or equal to the maximum size of memory requested. The allocation component  128  may then instruct the balloon driver  126  to inflate the balloon driver  125  with the guest memory from the identified entry. Allocation component  128  is discussed in more detail below in regards to  FIG.  2   . 
     In some implementations, memory manager  122  may be associated with a particular level of privilege that may be the same or similar to protection levels (e.g., processor protection rings). The privilege level may indicate an access level to computing devices (e.g., memory, processor, or other virtual or physical resources). In one example, the privilege levels may correspond generally to a user mode (e.g., reduced privilege mode, non-root mode, non-privileged mode) and a hypervisor mode (e.g., enhanced privilege mode, kernel mode, root mode). In some implementations, memory manager may execute in a user mode to access resources assigned to the execution environments and may be restricted from accessing resources associated with kernel space or with another user space process (e.g., other portion of user space). In some implementations, balloon driver and allocation component may execute in the hypervisor mode to access resources associated with the kernel space and the user space. In other examples, there may be a plurality of privilege levels, and the privilege levels may include a first level (e.g., ring  0 ) associated with a hypervisor/kernel, a second and third level (e.g., ring  1 - 2 ), and a fourth level (e.g., ring  3 ) that may be associated with user space applications. In some implementations, memory manager  122  may communicate with memory balloon  124 , balloon driver  126  and/or allocation component  128  using a context switch (e.g., system call or hypercall). 
     Hardware devices  130  may provide hardware resources and functionality for performing computing tasks. Hardware devices  130  may include one or more physical storage devices  132 , one or more physical processing devices  134 , other computing devices, or a combination thereof. One or more of hardware devices  130  may be split up into multiple separate devices or consolidated into one or more hardware devices. Some of the hardware device shown may be absent from hardware devices  130  and may instead be partially or completely emulated by executable code. 
     Physical storage devices  132  may include any data storage device that is capable of storing digital data and may include volatile or non-volatile data storage. Volatile data storage (e.g., non-persistent storage) may store data for any duration of time but may lose the data after a power cycle or loss of power. Non-volatile data storage (e.g., persistent storage) may store data for any duration of time and may retain the data beyond a power cycle or loss of power. In one example, physical storage devices  132  may be physical memory and may include volatile memory devices (e.g., random access memory (RAM)), non-volatile memory devices (e.g., flash memory, NVRAM), and/or other types of memory devices. In another example, physical storage devices  132  may include one or more mass storage devices, such as hard drives, solid state drives (SSD)), other data storage devices, or a combination thereof. In a further example, physical storage devices  132  may include a combination of one or more memory devices, one or more mass storage devices, other data storage devices, or a combination thereof, which may or may not be arranged in a cache hierarchy with multiple levels. 
     Physical processing devices  134  may include one or more processors that are capable of executing the computing tasks. Physical processing devices  134  may be a single core processor that is capable of executing one instruction at a time (e.g., single pipeline of instructions) or may be a multi-core processor that simultaneously executes multiple instructions. The instructions may encode arithmetic, logical, or I/O operations. In one example, physical processing devices  134  may be implemented as a single integrated circuit, two or more integrated circuits, or may be a component of a multi-chip module (e.g., in which individual microprocessor dies are included in a single integrated circuit package and hence share a single socket). A physical processing device may also be referred to as a central processing unit (“CPU”). 
     Network  140  may be a public network (e.g., the internet), a private network (e.g., a local area network (LAN), a wide area network (WAN)), or a combination thereof. In one example, network  140  may include a wired or a wireless infrastructure, which may be provided by one or more wireless communications systems, such as a wireless fidelity (WiFi) hotspot connected with the network  140  and/or a wireless carrier system that can be implemented using various data processing equipment, communication towers, etc. 
       FIG.  2    is a block diagram illustrating example components and modules of computer system  200 , in accordance with one or more aspects of the present disclosure. Computer system  200  may comprise executable code that implements one or more of the components and modules and may be implemented within a hypervisor, a host operating system, a guest operating system, hardware firmware, or a combination thereof In the example shown, computer system  200  may include allocation component  128 , balloon driver  126 , memory manager  122 , and guest memory  230 . Allocation component  128  may include free memory manager  212 , search module  214 , and instruction module  216 . Guest memory  230  may be similar to guest memory  114 A-C, and may include unreserved partition  232  and reserved partition  234 . Unreserved partition  232  may include any portion of guest memory (e.g., guest memory pages) that is available for use by a execution environment (e.g., execution environment  110 A-C). Reserved partition  234  may include any portion of guest memory that is used to inflate a memory balloon (e.g., memory balloon  124 ). For example, the memory pages in reserved partition  234  may be pinned in the memory balloon or placed in a reserved area of the host operating system associated with the memory balloon (thus inaccessible to the execution environment). In some implementations, memory manager  122  may operate in user space, while balloon driver  126  and allocation component  128  may operate in kernel space. 
     Free memory manager  212  may maintain a list free (e.g., unused) memory pages in free memory table  225 . The list of free memory pages may relate to one or more execution environments  110 A-C (e.g., guest memory of a container). Free memory table  225  may be any type of data structure used to store records of memory pages that are contiguous in a guest address space. Each entry in the free memory table  225  may reference a set of one or more contiguous standard memory pages, one or more contiguous huge pages, or any combination thereof. In some implementations, free memory manager  212  may implement a buddy memory allocation technique and free memory pages may be maintained in a buddy allocated data structure. The buddy memory allocation technique is an algorithm that manages memory in power of two increments. In particular, guest memory may be broken up into blocks of pages where each block is a power of two number of pages. The exponent for the power of two sized block may be referred to as an order. For example, order  0  may be indicative of free page blocks of size  2   0  (e.g., one memory page), order  1  may be indicative of free page blocks of size  2   1  (e.g., two memory pages), order  10  may be indicative of free page blocks of size  2   10  (e.g., 1024 memory pages), etc. If a block of a desired size is not available, a larger block may be broken up in half, where one half may be used for allocation consideration and the other half is placed into free memory table  225  for a lower order. If the half used for consideration is too large, then the half may be further broken up into two more halves, and so on until the desired size is available. This allows allocation component  128  to divide the guest memory into partitions to satisfy a memory request. 
     Memory manager  122  may send a memory request to allocation component  128  for guest memory to be made available to the hypervisor. In an example, memory manager  122  may send the memory request in response to detecting a low amount of available hypervisor memory  123  by examining resources or performance counters. In another example, memory manager  122  may receive a notification from performance monitoring software indicating that a low hypervisor memory  123  condition exists. The memory request may specify a size range of guest memory requested. For example, the memory request may include a minimum size of guest memory requested and a maximum size of guest memory requested. In some implementations, the minimum size may be a standard memory page and the maximum size may be a huge page. In some implementations, the minimum size may be a huge page and the maximum size may be multiple huge pages. Those skilled in the art would understand that any size may be used for the minimum size of guest memory requested and the maximum size of guest memory requested. 
     Search module  214  may search free memory table  225  for a set of guest memory that is within the size range specified in the memory request. In an example, search component may begin the looking up the smallest available order and determining whether the block size of that order will satisfy the memory request. Responsive to the block size not satisfying the memory request, search module  214  may move towards the next smallest available order. Once an entry is located that can satisfy the memory request (e.g., a block size between the minimum size of guest memory requested and the maximum size of guest memory requested), instruction module  216  may instruct the balloon driver  126  to mark the memory pages that are correlated to that entry as reserved (e.g., inflate the memory balloon), and release the memory pages to the memory manager  112 . Free memory manager  212  may then update the free memory table  225  by removing the entry. 
     In an illustrative example, free memory table  225  may include entries of 4 KB, 1 MB, 2 MB, and 4 MB of free memory pages. The hypervisor may request a minimum of ½ MB of guest memory, and a maximum of 2 MB of guest memory. In response, search module  214  may query the free memory table  225  starting from the smallest available order, and identify the 4 KB entry. Free memory manager  212  may determine that the 4 KB entry will not satisfy the memory request, then move towards the next smallest available order, and identify the 1 MB entry. Since the 1 MB entry is greater than the minimum requested size of ½ MB, and less than the maximum requested size of 2 MB, instruction module  216  may then instruct balloon driver  220  to release the block of memory pages of the 2 MB entry to the hypervisor. 
     In some implementations, free memory table  225  may not include an entry to satisfy a memory request. Accordingly, the search module  214  may identify an entry with a set of contiguous memory pages larger than the size range of the memory request. The instruction module  216  may then break up the identified set until a portion of the set can satisfy the memory request, upon which that portion may be released to the hypervisor. The remainder of the set may be placed into free memory table  225  for a lower order. As such, a set of contiguous memory pages is not broken up unless it exceeds the maximum requested size. 
     In an illustrative example, free memory table  225  may include entries of 4 KB, 4 MB, and 8 MB of contiguous free memory pages. The hypervisor may request a minimum of ½ MB of guest memory, and a maximum of 2 MB of guest memory. In response, search module  214  may query the free memory table  225  starting from the smallest available order, and identify the 4 KB entry. Free memory manager  212  may determine that the 4 KB entry will not satisfy the memory request, then move towards the next smallest available order, and identify the 4 MB entry. Since the 4 MB block is greater than the maximum requested size of 2 MB, instruction module  216  may instruct memory manager  212  to break up the block into two blocks of 2 MB each, and update the free memory table  225 . Search module  214  may then select one of 2 MB blocks, determine that the block is greater than the minimum requested size of ½ MB, and equal to the maximum requested size of 2 MB, and instruction module  216  may instruct balloon driver  126  to release this block of memory pages to the hypervisor. 
     In some implementations, search module  214  may not identify any suitable entries in free memory table  225 . Accordingly, instruction module  216  may instruct the execution environment to page-out (e.g., write memory pages to disk) a portion of guest memory to free some guest memory. Free memory manger  212  may then update free memory table  225  and search module  214  may initiate the search process again by querying free memory table  225  starting from the smallest available order. In some implementations, free memory manager  212  may periodically analyze guest memory  230  to update the free memory table  225 . 
       FIG.  3    depicts a flow diagram of an illustrative example of a method  300  for inflating a memory balloon with a set of guest memory within a requested range, in accordance with one or more aspects of the present disclosure. Method  300  and each of its individual functions, routines, subroutines, or operations may be performed by one or more processors of the computer device executing the method. In certain implementations, method  300  may be performed by a single processing thread. Alternatively, method  300  may be performed by two or more processing threads, each thread executing one or more individual functions, routines, subroutines, or operations of the method. In an illustrative example, the processing threads implementing method  300  may be synchronized (e.g., using semaphores, critical sections, and/or other thread synchronization mechanisms). Alternatively, the processes implementing method  300  may be executed asynchronously with respect to each other. 
     For simplicity of explanation, the methods of this disclosure are depicted and described as a series of acts. However, acts in accordance with this disclosure can occur in various orders and/or concurrently, and with other acts not presented and described herein. Furthermore, not all illustrated acts may be required to implement the methods in accordance with the disclosed subject matter. In addition, those skilled in the art will understand and appreciate that the methods could alternatively be represented as a series of interrelated states via a state diagram or events. Additionally, it should be appreciated that the methods disclosed in this specification are capable of being stored on an article of manufacture to facilitate transporting and transferring such methods to computing devices. The term “article of manufacture,” as used herein, is intended to encompass a computer program accessible from any computer-readable device or storage media. In one implementation, method  300  may be performed by a kernel of a hypervisor as shown in  FIG.  1    or by an executable code of a host machine (e.g., host operating system or firmware), an execution environment (e.g., guest operating system or virtual firmware), other executable code, or a combination thereof 
     Method  300  may be performed by processing devices of a server device or a client device and may begin at block  302 . At block  302 , the operating systems of a hypervisor running an execution environment maintains a list of free memory pages related to the execution environment. Each entry in the list may reference a set of memory pages that are contiguous in a guest address space. The list may be maintained in a buddy allocated data structure. In some implementations, the execution environment may be a container, a virtual machine, an application, etc. 
     At block  304 , the operating system of the hypervisor receives, from an application executing on the hypervisor, a memory request for guest memory to be made available to the hypervisor. The memory request may include a minimum size of guest memory requested and a maximum size of guest memory. For example, the minimum size of memory requested may be a standard memory page and the maximum size of memory requested may be a huge page. In some implementations, the request may be sent using a system call or a hypercall. 
     At block  306 , responsive to identifying a set of contiguous guest memory pages in the list of free memory pages that is greater than or equal to the minimum size of memory requested, and less than or equal to the maximum size of memory requested, the operating system releases the set of contiguous guest memory pages to the hypervisor. For example, the operating system may identify the smallest set of contiguous guest memory pages that is greater than or equal to the minimum size of the memory requested and less than or equal to the maximum size of memory requested. The released set of contiguous guest memory pages may be placed in a reserved memory pool (e.g., a memory balloon). 
     In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the operating system may satisfy the memory request by allocating a part of a portion of guest memory greater than the maximum size of memory requested (e.g., break apart a portion of guest memory). In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the operating system may page-out a portion of guest memory. Responsive to completing the operations described herein above with references to block  306 , the method may terminate. 
       FIG.  4    depicts a block diagram of a computer system  400  operating in accordance with one or more aspects of the present disclosure. Computer system  400  may be the same or similar to computer system  200  and computing device  100  and may include one or more processing devices and one or more memory devices. In the example shown, computer system  400  may include free memory manager  410 , search module  420 , and an instruction module  430 . 
     Free memory manager  410  may maintain a list of free memory pages related to an execution environment. Each entry in the list may reference a set of memory pages that are contiguous in a guest address space. The list may be maintained in a buddy allocated data structure. 
     Search module  420  may receive, from an management application of a hypervisor, a memory request for guest memory to be made available to the hypervisor. The memory request may include a minimum size of guest memory requested and a maximum size of guest memory. For example, the minimum size of memory requested may be a standard memory page and the maximum size of memory requested may be a huge page. Search module  420  may search the list of free memory pages for a set of memory pages to satisfy the memory request. 
     Responsive to search module  420  identifying a set of contiguous guest memory pages in the list of free memory pages that is greater than or equal to the minimum size of memory requested, and less than or equal to the maximum size of memory requested, instruction module  430  may release the set of contiguous guest memory pages to the hypervisor. For example, search module  420  may identify the smallest set of contiguous guest memory pages that is greater than or equal to the minimum size of the memory requested and less than or equal to the maximum size of memory requested. The released set of contiguous guest memory pages may be placed in a reserved memory pool (e.g., a memory balloon). 
     In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the free memory manager  410  may satisfy the memory request by allocating a part of a portion of guest memory greater than the maximum size of memory requested (e.g., break apart a portion of guest memory). In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the instruction module may page-out a portion of guest memory. 
       FIG.  5    depicts a flow diagram of one illustrative example of a method  500  for inflating a memory balloon with a set of guest memory within a requested range, in accordance with one or more aspects of the present disclosure. Method  500  may be similar to method  500  and may be performed in the same or a similar manner as described above in regards to method  300 . Method  500  may be performed by processing devices of a server device or a client device and may begin at block  502 . 
     At block  502 , a processing device maintains a list of free memory pages. Each entry in the list may reference a set of memory pages that are contiguous in a guest address space. The list may be maintained in a buddy allocated data structure. In some implementations, the processing device may run a container, a virtual machine, an application, etc. 
     At block  504 , the processing device receives, from a management application of a hypervisor, a memory request for guest memory to be made available to the hypervisor. The memory request may include a minimum size of guest memory requested and a maximum size of guest memory. For example, the minimum size of memory requested may be a standard memory page and the maximum size of memory requested may be a huge page. 
     At block  506 , responsive to identifying a set of contiguous guest memory pages in the list of free memory pages that is greater than or equal to the minimum size of memory requested, and less than or equal to the maximum size of memory requested, the processing device releases the set of contiguous guest memory pages to the hypervisor. For example, the processing device may identify the smallest set of contiguous guest memory pages that is greater than or equal to the minimum size of the memory requested and less than or equal to the maximum size of memory requested. The released set of contiguous guest memory pages may be placed in a reserved memory pool (e.g., a memory balloon). 
     In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the processing device may satisfy the memory request by allocating a part of a portion of guest memory greater than the maximum size of memory requested (e.g., break apart a portion of guest memory). In some implementations, responsive to failing to identify, in the list of free memory pages, a set of contiguous guest memory pages that is greater than or equal to the minimum size of memory requested and less than or equal to the maximum size of memory requested, the processing device may page-out a portion of guest memory. Responsive to completing the operations described herein above with references to block  506 , the method may terminate. 
       FIG.  6    depicts a block diagram of a computer system operating in accordance with one or more aspects of the present disclosure. In various illustrative examples, computer system  600  may correspond to computing device  100  of  FIG.  1    or computer system  200  of  FIG.  2   . The computer system may be included within a data center that supports virtualization. Virtualization within a data center results in a physical system being virtualized using execution environments to consolidate the data center infrastructure and increase operational efficiencies. A execution environment may be a program-based emulation of computer hardware. For example, the execution environment may operate based on computer architecture and functions of computer hardware resources associated with hard disks or other such memory. The execution environment may emulate a physical computing environment, but requests for a hard disk or memory may be managed by a virtualization layer of a computing device to translate these requests to the underlying physical computing hardware resources. This type of virtualization results in multiple execution environments sharing physical resources. 
     In certain implementations, computer system  600  may be connected (e.g., via a network, such as a Local Area Network (LAN), an intranet, an extranet, or the Internet) to other computer systems. Computer system  600  may operate in the capacity of a server or a client computer in a client-server environment, or as a peer computer in a peer-to-peer or distributed network environment. Computer system  600  may be provided by a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any device capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that device. Further, the term “computer” shall include any collection of computers that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methods described herein. 
     In a further aspect, the computer system  600  may include a processing device  602 , a volatile memory  604  (e.g., random access memory (RAM)), a non-volatile memory  606  (e.g., read-only memory (ROM) or electrically-erasable programmable ROM (EEPROM)), and a data storage device  616 , which may communicate with each other via a bus  608 . 
     Processing device  602  may be provided by one or more processors such as a general purpose processor (such as, for example, a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a microprocessor implementing other types of instruction sets, or a microprocessor implementing a combination of types of instruction sets) or a specialized processor (such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or a network processor). 
     Computer system  600  may further include a network interface device  622 . Computer system  600  also may include a video display unit  610  (e.g., an LCD), an alphanumeric input device  612  (e.g., a keyboard), a cursor control device  614  (e.g., a mouse), and a signal generation device  620 . 
     Data storage device  616  may include a non-transitory computer-readable storage medium  624  on which may store instructions  626  encoding any one or more of the methods or functions described herein, including instructions for implementing methods  300  or  500  and for allocation component  122 , and modules illustrated in  FIGS.  1  and  2   . 
     Instructions  626  may also reside, completely or partially, within volatile memory  604  and/or within processing device  602  during execution thereof by computer system  600 , hence, volatile memory  604  and processing device  602  may also constitute machine-readable storage media. 
     While computer-readable storage medium  624  is shown in the illustrative examples as a single medium, the term “computer-readable storage medium” shall include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of executable instructions. The term “computer-readable storage medium” shall also include any tangible medium that is capable of storing or encoding a set of instructions for execution by a computer that cause the computer to perform any one or more of the methods described herein. The term “computer-readable storage medium” shall include, but not be limited to, solid-state memories, optical media, and magnetic media. 
     The methods, components, and features described herein may be implemented by discrete hardware components or may be integrated in the functionality of other hardware components such as ASICS, FPGAs, DSPs or similar devices. In addition, the methods, components, and features may be implemented by firmware modules or functional circuitry within hardware devices. Further, the methods, components, and features may be implemented in any combination of hardware devices and computer program components, or in computer programs. 
     Unless specifically stated otherwise, terms such as “initiating,” “transmitting,” “receiving,” “analyzing,” or the like, refer to actions and processes performed or implemented by computer systems that manipulates and transforms data represented as physical (electronic) quantities within the computer system registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. Also, the terms “first,” “second,” “third,” “fourth,” etc. as used herein are meant as labels to distinguish among different elements and may not have an ordinal meaning according to their numerical designation. 
     Examples described herein also relate to an apparatus for performing the methods described herein. This apparatus may be specially constructed for performing the methods described herein, or it may comprise a general-purpose computer system selectively programmed by a computer program stored in the computer system. Such a computer program may be stored in a computer-readable tangible storage medium. 
     The methods and illustrative examples described herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used in accordance with the teachings described herein, or it may prove convenient to construct more specialized apparatus to perform methods  300  or  500  and one or more of its individual functions, routines, subroutines, or operations. Examples of the structure for a variety of these systems are set forth in the description above. 
     The above description is intended to be illustrative, and not restrictive. Although the present disclosure has been described with references to specific illustrative examples and implementations, it will be recognized that the present disclosure is not limited to the examples and implementations described. The scope of the disclosure should be determined with reference to the following claims, along with the full scope of equivalents to which the claims are entitled.