DOCSLIB.ORG

Exokernel: an Operating System Architecture for Application-Level Resource Management

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exokernel: an Operating System Architecture for Application-Level Resource Management Exokernel: An Operating System Architecture for Application-Level Resource Management Dawson R. Engler, M. Frans Kaashoek, and James O'Toole Jr. M.I.T. Laboratory for Computer Science Cambridge, MA 02139, U.S.A engler, kaashoek, james ¡ @lcs.mit.edu ¢¤£¦¥¨§¨© § inappropriate for three main reasons: it denies applications the ad- vantages of domain-speci®c optimizations, it discourages changes Traditional operating systems limit the performance, ¯exibility, and to the implementations of existing abstractions, and it restricts the functionality of applications by ®xing the interface and implemen- ¯exibility of application builders, since new abstractions can only tation of operating system abstractions such as interprocess com- be added by awkward emulation on top of existing ones (if they can munication and virtual memory. The exokernel operating system be added at all). architecture addresses this problem by providing application-level We believe these problems can be solved through application- management of physical resources. In the exokernel architecture, a level (i.e., untrusted) resource management. To this end, we have small kernel securely exports all hardware resources through a low- designed a new operating system architecture, exokernel, in which level interface to untrusted library operating systems. Library op- traditional operating system abstractions, such as virtual memory erating systems use this interface to implement system objects and (VM) and interprocess communication (IPC), are implemented en- policies. This separation of resource protection from management tirely at application level by untrusted software. In this architecture, allows application-speci®c customization of traditional operating a minimal kernelÐwhich we call an exokernelÐsecurely multi- system abstractions by extending, specializing, or even replacing plexes available hardware resources. Library operating systems, libraries. working above the exokernel interface, implement higher-level ab- We have implemented a prototype exokernel operating system. stractions. Application writers select libraries or implement their Measurements show that most primitive kernel operations (such own. New implementations of library operating systems are incor- as exception handling and protected control transfer) are ten to 100 porated by simply relinking application executables. times faster than in Ultrix, a mature monolithic UNIX operating sys- Substantial evidence exists that applications can bene®t greatly tem. In addition, we demonstrate that an exokernel allows applica- from having more control over how machine resources are used tions to control machineresources in ways not possiblein traditional to implement higher-level abstractions. Appel and Li [5] reported operating systems. For instance, virtual memory and interprocess that the high cost of general-purpose virtual memory primitives communication abstractions are implemented entirely within an reduces the performance of persistent stores,garbage collectors,and application-level library. Measurements show that application-level distributed shared memory systems. Cao et al. [10] reported that virtual memory and interprocess communication primitives are ®ve application-level control over ®le caching can reduce application to 40 times faster than Ultrix's kernel primitives. Compared to running time by 45%. Harty and Cheriton [26] and Krueger et state-of-the-art implementations from the literature, the prototype al. [30] showed how application-speci®c virtual memory policies exokernel system is at least ®ve times faster on operations such as can increase application performance. Stonebraker [47] argued exception dispatching and interprocess communication. that inappropriate ®le-system implementation decisions can have a dramatic impact on the performance of databases. Thekkath and §¨© ¦ § Levy [50] demonstrated that exceptions can be made an order of magnitude faster by deferring signal handling to applications. Operating systems de®ne the interface between applications and To provide applications control over machine resources, an ex- physical resources. Unfortunately, this interface can signi®cantly okernel de®nes a low-level interface. The exokernel architecture is limit the performance and implementation freedom of applications. founded on and motivated by a single, simple, and old observation: Traditionally, operating systems hide information about machine the lower the level of a primitive, the more ef®ciently it can be resources behind high-level abstractions such as processes, ®les, implemented, and the more latitude it grants to implementors of address spaces and interprocess communication. These abstrac- higher-level abstractions. tions de®ne a virtual machine on which applications execute; their To provide an interface that is as low-level as possible (ideally, implementation cannot be replaced or modi®ed by untrusted appli- just the hardware interface), an exokernel designer has a single cations. Hardcoding the implementations of these abstractions is overriding goal: to separate protection from management. For instance, an exokernel should protect framebuffers without under- This research was supported in part by the Advanced Research Projects Agency under contract N00014-94-1-0985 and by a NSF National Young Investigator Award. standing windowing systems and disks without understanding ®le systems. One approach is to give each application its own virtual Copyright c 1995 by the Association for Computing Machinery, Inc. Permission to make digital or hard copies of part or all of this work for personal or classroom use machine [17]. As we discuss in Section 8, virtual machines can is granted without fee provided that copies are not made or distributed for pro®t or have severe performance penalties. Therefore, an exokernel uses a commercial advantage and that new copies bear this notice and the full citation on the different approach: it exports hardware resources rather than emu- ®rst page. Copyrights for components of this WORK owned by others than ACM must lating them, which allows an ef®cient and simple implementation. be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires An exokernel employs three techniques to export resources securely. prior speci®c permission and/or a fee. Request Permissions from Publications Dept, First, by using secure bindings, applications can securely bind to ACM Inc., Fax +1 (212) 869-0481, or [email protected] . machine resources and handle events. Second, by using visible re- source revocation, applications participate in a resource revocation stractions and show how the exokernel architecture addresses these protocol. Third, by using an abort protocol, an exokernel can break problems. secure bindings of uncooperative applications by force. ¥¨§ ¤ £¨ ¤£ "! ¢# $ ¢¤£¦¥¨§¨© §¦¥ We have implemented a prototype exokernel system based on secure bindings, visible revocation, and abort protocols. It includes an exokernel (Aegis) and an untrusted library operating system The essential observation about abstractions in traditional operating (ExOS). We use this system to demonstrate several important prop- systems is that they are overly general. Traditional operating sys- erties of the exokernel architecture: (1) exokernels can be made tems attempt to provide all the features needed by all applications. ef®cient due to the limited number of simple primitives they must As previously noted by Lampson and Sproul [32], Anderson et provide; (2) low-level secure multiplexing of hardware resources al. [4] and Massalin and Pu [36], general-purpose implementations can be provided with low overhead; (3) traditional abstractions, of abstractions force applications that do not need a given feature to such as VM and IPC, can be implemented ef®ciently at application pay substantial overhead costs. This longstanding problem has be- level, where they can be easily extended, specialized, or replaced; come more important with explosive improvements in raw hardware and (4) applications can create special-purpose implementations of performance and enormous growth in diversity of the application abstractions, tailored to their functionality and performance needs. software base. We argue that preventing the modi®cation of the implementation of these high-level abstractions can reduce the per- In practice, our prototype exokernel system provides applica- formance, increase the complexity, and limit the functionality of tions with greater ¯exibility and better performance than mono- application programs. lithic and microkernel systems. Aegis's low-level interface allows application-level software such as ExOS to manipulate resources Fixed high-level abstractions hurt application performance be- very ef®ciently. Aegis's protected control transfer is almost seven cause there is no single way to abstract physical resources or to times faster than the best reported implementation [33]. Aegis's implement an abstraction that is best for all applications. In im- exception dispatch is ®ve times faster than the best reported imple- plementing an abstraction, an operating system is forced to make mentation [50]. On identical hardware, Aegis's exception dispatch trade-offs between support for sparse or dense address spaces, and control transfer are roughly two orders of magnitude faster than read-intensive or write-intensive workloads, etc. Any such trade- in Ultrix 4.2, a mature monolithic system.
Load more

Recommended publications
  • The Case for Compressed Caching in Virtual Memory Systems
    THE ADVANCED COMPUTING SYSTEMS ASSOCIATION The following paper was originally published in the Proceedings of the USENIX Annual Technical Conference Monterey, California, USA, June 6-11, 1999 The Case for Compressed Caching in Virtual Memory Systems _ Paul R. Wilson, Scott F. Kaplan, and Yannis Smaragdakis aUniversity of Texas at Austin © 1999 by The USENIX Association All Rights Reserved Rights to individual papers remain with the author or the author's employer. Permission is granted for noncommercial reproduction of the work for educational or research purposes. This copyright notice must be included in the reproduced paper. USENIX acknowledges all trademarks herein. For more information about the USENIX Association: Phone: 1 510 528 8649 FAX: 1 510 548 5738 Email: [email protected] WWW: http://www.usenix.org The Case for Compressed Caching in Virtual Memory Systems Paul R. Wilson, Scott F. Kaplan, and Yannis Smaragdakis Dept. of Computer Sciences University of Texas at Austin Austin, Texas 78751-1182 g fwilson|sfkaplan|smaragd @cs.utexas.edu http://www.cs.utexas.edu/users/oops/ Abstract In [Wil90, Wil91b] we proposed compressed caching for virtual memory—storing pages in compressed form Compressed caching uses part of the available RAM to in a main memory compression cache to reduce disk pag- hold pages in compressed form, effectively adding a new ing. Appel also promoted this idea [AL91], and it was level to the virtual memory hierarchy. This level attempts evaluated empirically by Douglis [Dou93] and by Russi- to bridge the huge performance gap between normal (un- novich and Cogswell [RC96]. Unfortunately Douglis’s compressed) RAM and disk.
    [Show full text]
  • Extracting Compressed Pages from the Windows 10 Virtual Store WHITE PAPER | EXTRACTING COMPRESSED PAGES from the WINDOWS 10 VIRTUAL STORE 2
    white paper Extracting Compressed Pages from the Windows 10 Virtual Store WHITE PAPER | EXTRACTING COMPRESSED PAGES FROM THE WINDOWS 10 VIRTUAL STORE 2 Abstract Windows 8.1 introduced memory compression in August 2013. By the end of 2013 Linux 3.11 and OS X Mavericks leveraged compressed memory as well. Disk I/O continues to be orders of magnitude slower than RAM, whereas reading and decompressing data in RAM is fast and highly parallelizable across the system’s CPU cores, yielding a significant performance increase. However, this came at the cost of increased complexity of process memory reconstruction and thus reduced the power of popular tools such as Volatility, Rekall, and Redline. In this document we introduce a method to retrieve compressed pages from the Windows 10 Memory Manager Virtual Store, thus providing forensics and auditing tools with a way to retrieve, examine, and reconstruct memory artifacts regardless of their storage location. Introduction Windows 10 moves pages between physical memory and the hard disk or the Store Manager’s virtual store when memory is constrained. Universal Windows Platform (UWP) applications leverage the Virtual Store any time they are suspended (as is the case when minimized). When a given page is no longer in the process’s working set, the corresponding Page Table Entry (PTE) is used by the OS to specify the storage location as well as additional data that allows it to start the retrieval process. In the case of a page file, the retrieval is straightforward because both the page file index and the location of the page within the page file can be directly retrieved.
    [Show full text]
  • Memory Protection File B [RWX] File D [RW] File F [R] OS GUEST LECTURE
    11/17/2018 Operating Systems Protection Goal: Ensure data confidentiality + data integrity + systems availability Protection domain = the set of accessible objects + access rights File A [RW] File C [R] Printer 1 [W] File E [RX] Memory Protection File B [RWX] File D [RW] File F [R] OS GUEST LECTURE XIAOWAN DONG Domain 1 Domain 2 Domain 3 11/15/2018 1 2 Private Virtual Address Space Challenges of Sharing Memory Most common memory protection Difficult to share pointer-based data Process A virtual Process B virtual Private Virtual addr space mechanism in current OS structures addr space addr space Private Page table Physical addr space ◦ Data may map to different virtual addresses Each process has a private virtual in different address spaces Physical address space Physical Access addr space ◦ Set of accessible objects: virtual pages frame no Rights Segment 3 mapped … … Segment 2 ◦ Access rights: access permissions to P1 RW each virtual page Segment 1 P2 RW Segment 1 Recorded in per-process page table P3 RW ◦ Virtual-to-physical translation + P4 RW Segment 2 access permissions … … 3 4 1 11/17/2018 Challenges of Sharing Memory Challenges for Memory Sharing Potential duplicate virtual-to-physical Potential duplicate virtual-to-physical translation information for shared Process A page Physical Process B page translation information for shared memory table addr space table memory Processor ◦ Page table is per-process at page ◦ Single copy of the physical memory, multiple granularity copies of the mapping info (even if identical) TLB L1 cache
    [Show full text]
  • Paging: Smaller Tables
    20 Paging: Smaller Tables We now tackle the second problem that paging introduces: page tables are too big and thus consume too much memory. Let’s start out with a linear page table. As you might recall1, linear page tables get pretty 32 12 big. Assume again a 32-bit address space (2 bytes), with 4KB (2 byte) pages and a 4-byte page-table entry. An address space thus has roughly 232 one million virtual pages in it ( 212 ); multiply by the page-table entry size and you see that our page table is 4MB in size. Recall also: we usually have one page table for every process in the system! With a hundred active processes (not uncommon on a modern system), we will be allocating hundreds of megabytes of memory just for page tables! As a result, we are in search of some techniques to reduce this heavy burden. There are a lot of them, so let’s get going. But not before our crux: CRUX: HOW TO MAKE PAGE TABLES SMALLER? Simple array-based page tables (usually called linear page tables) are too big, taking up far too much memory on typical systems. How can we make page tables smaller? What are the key ideas? What inefficiencies arise as a result of these new data structures? 20.1 Simple Solution: Bigger Pages We could reduce the size of the page table in one simple way: use bigger pages. Take our 32-bit address space again, but this time assume 16KB pages. We would thus have an 18-bit VPN plus a 14-bit offset.
    [Show full text]
  • Application Performance and Flexibility on Exokernel Systems
    Application Performance and Flexibility On Exokernel Systems –M. F. Kaashoek, D.R. Engler, G.R. Ganger et. al. Presented by Henry Monti Exokernel ● What is an Exokernel? ● What are its advantages? ● What are its disadvantages? ● Performance ● Conclusions 2 The Problem ● Traditional operating systems provide both protection and resource management ● Will protect processes address space, and manages the systems virtual memory ● Provides abstractions such as processes, files, pipes, sockets,etc ● Problems with this? 3 Exokernel's Solution ● The problem is that OS designers must try and accommodate every possible use of abstractions, and choose general solutions for resource management ● This causes the performance of applications to suffer, since they are restricted to general abstractions, interfaces, and management ● Research has shown that more application control of resources yields better performance 4 (Separation vs. Protection) ● An exokernel solves these problems by separating protection from management ● Creates idea of LibOS, which is like a virtual machine with out isolation ● Moves abstractions (processes, files, virtual memory, filesystems), to the user space inside of LibOSes ● Provides a low level interface as close to the hardware as possible 5 General Design Principles ● Exposes as much as possible of the hardware, most of the time using hardware names, allowing libOSes access to things like individual data blocks ● Provides methods to securely bind to resources, revoke resources, and an abort protocol that the kernel itself
    [Show full text]
  • Unikernel Monitors: Extending Minimalism Outside of the Box
    Unikernel Monitors: Extending Minimalism Outside of the Box Dan Williams Ricardo Koller IBM T.J. Watson Research Center Abstract Recently, unikernels have emerged as an exploration of minimalist software stacks to improve the security of ap- plications in the cloud. In this paper, we propose ex- tending the notion of minimalism beyond an individual virtual machine to include the underlying monitor and the interface it exposes. We propose unikernel monitors. Each unikernel is bundled with a tiny, specialized mon- itor that only contains what the unikernel needs both in terms of interface and implementation. Unikernel mon- itors improve isolation through minimal interfaces, re- Figure 1: The unit of execution in the cloud as (a) a duce complexity, and boot unikernels quickly. Our ini- unikernel, built from only what it needs, running on a tial prototype, ukvm, is less than 5% the code size of a VM abstraction; or (b) a unikernel running on a spe- traditional monitor, and boots MirageOS unikernels in as cialized unikernel monitor implementing only what the little as 10ms (8× faster than a traditional monitor). unikernel needs. 1 Introduction the application (unikernel) and the rest of the system, as defined by the virtual hardware abstraction, minimal? Minimal software stacks are changing the way we think Can application dependencies be tracked through the in- about assembling applications for the cloud. A minimal terface and even define a minimal virtual machine mon- amount of software implies a reduced attack surface and itor (or in this case a unikernel monitor) for the applica- a better understanding of the system, leading to increased tion, thus producing a maximally isolated, minimal exe- security.
    [Show full text]
  • X86 Memory Protection and Translation
    2/5/20 COMP 790: OS Implementation COMP 790: OS Implementation Logical Diagram Binary Memory x86 Memory Protection and Threads Formats Allocators Translation User System Calls Kernel Don Porter RCU File System Networking Sync Memory Device CPU Today’s Management Drivers Scheduler Lecture Hardware Interrupts Disk Net Consistency 1 Today’s Lecture: Focus on Hardware ABI 2 1 2 COMP 790: OS Implementation COMP 790: OS Implementation Lecture Goal Undergrad Review • Understand the hardware tools available on a • What is: modern x86 processor for manipulating and – Virtual memory? protecting memory – Segmentation? • Lab 2: You will program this hardware – Paging? • Apologies: Material can be a bit dry, but important – Plus, slides will be good reference • But, cool tech tricks: – How does thread-local storage (TLS) work? – An actual (and tough) Microsoft interview question 3 4 3 4 COMP 790: OS Implementation COMP 790: OS Implementation Memory Mapping Two System Goals 1) Provide an abstraction of contiguous, isolated virtual Process 1 Process 2 memory to a program Virtual Memory Virtual Memory 2) Prevent illegal operations // Program expects (*x) – Prevent access to other application or OS memory 0x1000 Only one physical 0x1000 address 0x1000!! // to always be at – Detect failures early (e.g., segfault on address 0) // address 0x1000 – More recently, prevent exploits that try to execute int *x = 0x1000; program data 0x1000 Physical Memory 5 6 5 6 1 2/5/20 COMP 790: OS Implementation COMP 790: OS Implementation Outline x86 Processor Modes • x86
    [Show full text]
  • CS 414/415 Systems Programming and Operating Systems
    1 MODERN SYSTEMS: EXTENSIBLE KERNELS AND CONTAINERS CS6410 Hakim Weatherspoon Motivation 2 Monolithic Kernels just aren't good enough? Conventional virtual memory isn't what userspace programs need (Appel + Li '91) Application-level control of caching gives 45% speedup (Cao et al '94) Application-specific VM increases performance (Krueger '93, Harty + Cheriton '92) Filesystems for databases (Stonebraker '81) And more... Motivation 3 Lots of problems… Motivation 4 Lots of problems…Lots of design opportunities! Motivation 5 Extensibility Security Performance Can we have all 3 in a single OS? From Stefan Savage’s SOSP 95 presentation Context for these papers 1990’s Researchers (mostly) were doing special purpose OS hacks Commercial market complaining that OS imposed big overheads on them OS research community began to ask what the best way to facilitate customization might be. In the spirit of the Flux OS toolkit… 2010’s containers: single-purpose appliances Unikernels: (“sealable”) single-address space Compile time specialized Motivation 7 1988-1995: lots of innovation in OS development Mach 3, the first “true” microkernel SPIN, Exokernel, Nemesis, Scout, SPACE, Chorus, Vino, Amoeba, etc... And even more design papers Motivation 8 Exploring new spaces Distributed computing Secure computing Extensible kernels (exokernel, unikernel) Virtual machines (exokernel) New languages (spin) New memory management (exokernel, unikernel) Exokernel Dawson R. Engler, M. Frans Kaashoek and James O’Toole Jr. Engler’s Master’s
    [Show full text]
  • Protection in the Think Exokernel Christophe Rippert, Jean-Bernard Stefani
    Protection in the Think exokernel Christophe Rippert, Jean-Bernard Stefani To cite this version: Christophe Rippert, Jean-Bernard Stefani. Protection in the Think exokernel. 4th CaberNet European Research Seminar on Advances in Distributed Systems, May 2001, Bertinoro, Italy. hal-00308882 HAL Id: hal-00308882 https://hal.archives-ouvertes.fr/hal-00308882 Submitted on 4 Aug 2008 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Protection in the Think exokernel Christophe Rippert,∗ Jean-Bernard Stefani† [email protected], [email protected] Introduction In this paper, we present our preliminary ideas concerning the adaptation of security and protection techniques in the Think exokernel. Think is our proposition of a distributed adaptable kernel, designed according to the exokernel architecture. After summing up the main motivations for using the exokernel architecture, we describe the Think exokernel as it has been implemented on a PowerPC machine. We then present the major protection and security techniques that we plan to adapt to the Think environment, and give an example of how some of these techniques can be combined with the Think model to provide fair and protected resource management.
    [Show full text]
  • OS Extensibility: Spin, Exo-Kernel and L4
    OS Extensibility: Spin, Exo-kernel and L4 Extensibility Problem: How? Add code to OS how to preserve isolation? … without killing performance? What abstractions? General principle: mechanisms in OS, policies through the extensions What mechanisms to expose? 2 Spin Approach to extensibility Co-location of kernel and extension Avoid border crossings But what about protection? Language/compiler forced protection Strongly typed language Protection by compiler and run-time Cannot cheat using pointers Logical protection domains No longer rely on hardware address spaces to enforce protection – no boarder crossings Dynamic call binding for extensibility 3 ExoKernel 4 Motivation for Exokernels Traditional centralized resource management cannot be specialized, extended or replaced Privileged software must be used by all applications Fixed high level abstractions too costly for good efficiency Exo-kernel as an end-to-end argument 5 Exokernel Philosophy Expose hardware to libraryOS Not even mechanisms are implemented by exo-kernel They argue that mechanism is policy Exo-kernel worried only about protection not resource management 6 Design Principles Track resource ownership Ensure protection by guarding resource usage Revoke access to resources Expose hardware, allocation, names and revocation Basically validate binding, then let library manage the resource 7 Exokernel Architecture 8 Separating Security from Management Secure bindings – securely bind machine resources Visible revocation – allow libOSes to participate in resource revocation Abort protocol
    [Show full text]
  • Composing Abstractions Using the Null-Kernel
    Composing Abstractions using the null-Kernel James Litton Deepak Garg University of Maryland Max Planck Institute for Software Systems Max Planck Institute for Software Systems [email protected] [email protected] Peter Druschel Bobby Bhattacharjee Max Planck Institute for Software Systems University of Maryland [email protected] [email protected] CCS CONCEPTS hardware, such as GPUs, crypto/AI accelerators, smart NICs/- • Software and its engineering → Operating systems; storage devices, NVRAM etc., and to efficiently support new Layered systems; • Security and privacy → Access control. application requirements for functionality such as transac- tional memory, fast snapshots, fine-grained isolation, etc., KEYWORDS that demand new OS abstractions that can exploit existing hardware in novel and more efficient ways. Operating Systems, Capability Systems At its core, the null-Kernel derives its novelty from being ACM Reference Format: able to support and compose across components, called Ab- James Litton, Deepak Garg, Peter Druschel, and Bobby Bhattachar- stract Machines (AMs) that provide programming interfaces jee. 2019. Composing Abstractions using the null-Kernel. In Work- at different levels of abstraction. The null-Kernel uses an ex- shop on Hot Topics in Operating Systems (HotOS ’19), May 13–15, 2019, Bertinoro, Italy. ACM, New York, NY, USA, 6 pages. https: tensible capability mechanism to control resource allocation //doi.org/10.1145/3317550.3321450 and use at runtime. The ability of the null-Kernel to support interfaces at different levels of abstraction accrues several 1 INTRODUCTION benefits: New hardware can be rapidly deployed using rela- tively low-level interfaces; high-level interfaces can easily Abstractions imply choice, one that OS designers must con- be built using low-level ones; and applications can benefit front when designing a programming interface to expose.
    [Show full text]
  • An Evolutionary Study of Linux Memory Management for Fun and Profit Jian Huang, Moinuddin K
    An Evolutionary Study of Linux Memory Management for Fun and Profit Jian Huang, Moinuddin K. Qureshi, and Karsten Schwan, Georgia Institute of Technology https://www.usenix.org/conference/atc16/technical-sessions/presentation/huang This paper is included in the Proceedings of the 2016 USENIX Annual Technical Conference (USENIX ATC ’16). June 22–24, 2016 • Denver, CO, USA 978-1-931971-30-0 Open access to the Proceedings of the 2016 USENIX Annual Technical Conference (USENIX ATC ’16) is sponsored by USENIX. An Evolutionary Study of inu emory anagement for Fun and rofit Jian Huang, Moinuddin K. ureshi, Karsten Schwan Georgia Institute of Technology Astract the patches committed over the last five years from 2009 to 2015. The study covers 4587 patches across Linux We present a comprehensive and uantitative study on versions from 2.6.32.1 to 4.0-rc4. We manually label the development of the Linux memory manager. The each patch after carefully checking the patch, its descrip- study examines 4587 committed patches over the last tions, and follow-up discussions posted by developers. five years (2009-2015) since Linux version 2.6.32. In- To further understand patch distribution over memory se- sights derived from this study concern the development mantics, we build a tool called MChecker to identify the process of the virtual memory system, including its patch changes to the key functions in mm. MChecker matches distribution and patterns, and techniues for memory op- the patches with the source code to track the hot func- timizations and semantics. Specifically, we find that tions that have been updated intensively.
    [Show full text]