L07b - Distributed Shared Memory

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<p>Memory is a crucial resource that impacts performance, and unused memory in a cluster can be utilized to enhance efficiency.</p> Signup and view all the answers

<p>The GMS asks how to effectively use peer memory for paging across a Local Area Network (LAN).</p> Signup and view all the answers

<p>The goal of DSM is to provide a shared memory abstraction, making it appear as though there is a single shared memory space.</p> Signup and view all the answers

<p>DFS utilizes cluster memory for cooperative caching of files to enhance access speeds.</p> Signup and view all the answers

<p>The common theme is efficient memory usage, focusing on optimizing peer memory utilization.</p> Signup and view all the answers

<p>GMS leverages the cluster's global memory to improve efficiency by using it as a faster surrogate for disk paging.</p> Signup and view all the answers

<p>After copying the shared page X, Host P's local memory increases by 1 while its global memory decreases by 1.</p> Signup and view all the answers

<p>If the oldest page is evicted from Host R's local memory, its local memory decreases and its global memory increases.</p> Signup and view all the answers

<p>The total memory pressure increases by 1 because page X is present in the working sets of both Host P and Host Q.</p> Signup and view all the answers

<p>GMS does not manage coherence for shared pages; it solely handles the paging.</p> Signup and view all the answers

<p>Idle nodes begin to store pages from active nodes, gradually becoming memory servers for peers.</p> Signup and view all the answers

<p>It indicates that local memory is used by the node itself, while global memory is dynamically allocated to store pages for other nodes.</p> Signup and view all the answers

<p>Age management aims to identify the globally oldest page for replacement to ensure balanced memory management across nodes.</p> Signup and view all the answers

<p>Host P must copy page X into its local memory while evicting another page Y from its global memory.</p> Signup and view all the answers

<p>If the globally oldest page is evicted from global memory and is clean, it can be discarded without writing it to disk.</p> Signup and view all the answers

<p>Host Q's local and global memory remains unchanged since it still utilizes page X in its working set.</p> Signup and view all the answers

<p>Cluster-wide memory pressure is managed by evicting or writing a page to disk when shared pages increase demand on memory resources.</p> Signup and view all the answers

<p>Epoch-based management distributes memory management tasks and limits the number of page replacements within a defined time frame.</p> Signup and view all the answers

<p>An epoch ends when either the time limit (T) or the number of replacements (M) is reached.</p> Signup and view all the answers

<p>The initiator calculates the minimum age of the M pages to be replaced and identifies pages older than this as candidates.</p> Signup and view all the answers

<p>Each node shares the age information of its pages, both local and global, with the initiator node.</p> Signup and view all the answers

<p>A node's weight represents the fraction of its pages expected to be replaced in the upcoming epoch.</p> Signup and view all the answers

<p>Dynamic assignments prevent a single node from becoming overburdened by managing memory responsibilities.</p> Signup and view all the answers

<p>If its age is greater, the page is identified as a replacement candidate and can be immediately discarded.</p> Signup and view all the answers

<p>It calculates age and weight information at the start of each epoch and uses that data to make local decisions.</p> Signup and view all the answers

<p>Historical usage helps the initiator predict future page replacements based on age information.</p> Signup and view all the answers

<p>The next initiator is chosen as the node with the highest weight distribution, indicating it is the least active.</p> Signup and view all the answers

<p>The initiator computes the minimum age of pages to identify replacement candidates for the upcoming epoch.</p> Signup and view all the answers

<p>The page must be sent to a peer for storage in its global cache.</p> Signup and view all the answers

<p>This information helps nodes plan for upcoming epochs and predict page replacement likelihood.</p> Signup and view all the answers

<p>The min age defines the threshold for determining which pages are candidates for replacement.</p> Signup and view all the answers

<p>GMS manages the allocation and freeing of page frames in the cluster-wide memory pool, allowing for efficient handling of page requests and memory reuse.</p> Signup and view all the answers

<p>GMS collects age information by having UBC intercept read/write calls and redirecting page faults for age tracking.</p> Signup and view all the answers

<p>The PFD maps a Universal ID (UID) to a corresponding physical page frame in memory or disk, facilitating efficient memory access.</p> Signup and view all the answers

<p>A UID consists of an IP address, a disk partition identifier, an i-node representing the related file or object, and an offset within the page.</p> Signup and view all the answers

<p>The GCD manages the mapping between UIDs and physical frame information contained in the Page Frame Directory across nodes.</p> Signup and view all the answers

<p>The POD tracks ownership information for pages, determining which node or process owns a particular page to ensure memory consistency.</p> Signup and view all the answers

<p>The pageout daemon collaborates with GMS to place clean pages into the cluster memory, enhancing memory reuse instead of discarding them.</p> Signup and view all the answers

<p>Upon a page fault, the virtual address is converted to a UID to identify the page's location across the cluster.</p> Signup and view all the answers

<p>The Distributed Hash Table enables efficient lookup of PFD information corresponding to UIDs without overloading any single node.</p> Signup and view all the answers

<p>A private page is accessible only by the owning process, while a shared page can be accessed by multiple processes.</p> Signup and view all the answers

<p>GMS combines UID mapping, global cache tracking, and ownership management to coordinate memory access across different nodes effectively.</p> Signup and view all the answers

<p>Intercepting read/write calls allows UBC to track the age of pages and redirect page faults to GMS for better memory management.</p> Signup and view all the answers

<p>The POD is a replicated data structure across all nodes, maintaining identical copies to ensure data consistency.</p> Signup and view all the answers

<p>GMS collaborates with the Free List to allocate and free page frames in a distributed manner across the cluster.</p> Signup and view all the answers

<p>The primary goal of GMS is to utilize idle memory from other nodes in a local area network for paging, reducing reliance on slower disk access.</p> Signup and view all the answers

<p>In GMS, the Virtual Memory Manager first checks for required pages in cluster memory before accessing the disk, whereas traditional systems directly fetch from disk on a page fault.</p> Signup and view all the answers

<p>Memory pressure refers to the high demand for memory resources by processes on a node, which may be contrasted with other idle nodes with available memory.</p> Signup and view all the answers

<p>The working set is the portion of virtual memory that is currently required by a process and is actually in physical memory at any given time.</p> Signup and view all the answers

<p>During a page fault, GMS first checks the cluster memory for the page; if it's not found, it then retrieves it from the disk.</p> Signup and view all the answers

<p>Private pages belong to a single process, while shared pages are accessed by multiple nodes running distributed applications.</p> Signup and view all the answers

<p>Network memory access can be faster due to high data transfer rates in modern networks like Gigabit Ethernet, compared to the slower access speeds and latencies associated with disk drives.</p> Signup and view all the answers

<p>Physical memory is dynamically split into local memory for processes and global memory for storing pages from peers, adjusting based on the node's activity.</p> Signup and view all the answers

<p>GMS ensures fault tolerance by storing clean pages in the cluster memory on the disk, preventing data loss during crashes.</p> Signup and view all the answers

<p>Dirty pages refer to modified pages that must be written back to the disk to ensure data is not lost.</p> Signup and view all the answers

<p>GMS reduces reliance on slow disk access by utilizing idle memory from other nodes, leading to faster data retrieval.</p> Signup and view all the answers

<p>Cluster memory is positioned between main memory and disk in the memory hierarchy.</p> Signup and view all the answers

<p>The coherence of shared pages is a concern because GMS does not handle it; the application must ensure coherence among processes accessing those pages.</p> Signup and view all the answers

<p>GMS can send pages to a peer node's memory instead of writing them to disk, allowing for efficient management of memory resources.</p> Signup and view all the answers

<p>The node retries by consulting the updated POD or going to the updated GCD to retrieve the page from the correct node or disk.</p> Signup and view all the answers

<p>In most situations, the POD and GCD are co-resident on the same node, minimizing network communication for lookups.</p> Signup and view all the answers

<p>The paging daemon starts evicting pages when the free list of available memory falls below a pre-defined threshold.</p> Signup and view all the answers

<p>Weight information is used to select a candidate node that can host the evicted page based on its load or replacement history.</p> Signup and view all the answers

<p>Unlike traditional daemons that send pages to disk, the GMS paging daemon sends the oldest pages to another node's memory.</p> Signup and view all the answers

<p>The Global Cache Directory (GCD) must be updated to reflect the new node as the Page Frame Directory (PFD) holder for the UID.</p> Signup and view all the answers

<p>Retrying allows the node to consult updated information, ensuring it retrieves the page from the correct node or disk.</p> Signup and view all the answers

<p>Misses are uncommon because they typically occur due to page replacement not communicated to the GCD or outdated POD information.</p> Signup and view all the answers

<p>Batch handling minimizes overhead associated with frequent updates and ensures smoother system performance.</p> Signup and view all the answers

<p>GMS implements global age management to distribute load evenly among nodes while optimizing memory usage.</p> Signup and view all the answers

<p>To map process virtual address space to physical memory and manage page faults.</p> Signup and view all the answers

<p>By caching disk-resident files in physical memory for faster access.</p> Signup and view all the answers

<p>Modifying the VM and UBC to interact with cluster memory instead of disk.</p> Signup and view all the answers

<p>It identifies pages that can be swapped out to free up physical memory.</p> Signup and view all the answers

<p>It requests the missing page from the GMS, checking both remote memory and disk.</p> Signup and view all the answers

<p>To maintain a list of available physical page frames for the VM and UBC.</p> Signup and view all the answers

<p>It is crucial for approximating the global Least Recently Used (LRU) algorithm.</p> Signup and view all the answers

<p>Memory accesses occur at the hardware level and are not directly observable by the OS.</p> Signup and view all the answers

<p>Dirty pages are written to disk to maintain system reliability.</p> Signup and view all the answers

<p>It queries cluster memory first for missing pages instead of defaulting to disk access.</p> Signup and view all the answers

<p>It allows for better coordination of memory resources across nodes in the cluster.</p> Signup and view all the answers

<p>It stores recent translations of virtual addresses to physical memory addresses to track page accesses.</p> Signup and view all the answers

<p>The UBC queries GMS first for missing pages before accessing the disk.</p> Signup and view all the answers

<p>It requires significant modifications to memory management at the system level.</p> Signup and view all the answers

<p>The POD tells each node which part of the Global Cache Directory (GCD) to consult for a given UID.</p> Signup and view all the answers

<p>The node queries the relevant part of the GCD to find the corresponding PFD for the UID.</p> Signup and view all the answers

<p>Upon a page fault, the node converts the virtual address to a UID and consults the POD to find the GCD owner.</p> Signup and view all the answers

<p>The PFD directs the node to the disk location where the page is stored.</p> Signup and view all the answers

<p>The POD is replicated across all nodes, ensuring that access is always local.</p> Signup and view all the answers

<p>Network communication is acceptable as it is often faster than disk access, making it efficient.</p> Signup and view all the answers

<p>In most cases, non-shared pages allow local handling of both the POD and GCD.</p> Signup and view all the answers

<p>Stale POD information can lead to the wrong node being contacted for a UID.</p> Signup and view all the answers

<p>The node sends a request to the owner node, which then queries the appropriate PFD to locate the page.</p> Signup and view all the answers

<p>The GCD maps UIDs to the node responsible for the relevant PFD, streamlining the query process.</p> Signup and view all the answers

<p>The PFD provides the final mapping of a UID to either a physical page frame in memory or to a disk location.</p> Signup and view all the answers

<p>If a page is evicted while a request is pending, the requesting node might get a page miss.</p> Signup and view all the answers

<p>The request may result in a miss if the target node has already evicted the requested page.</p> Signup and view all the answers

<p>The node converts the virtual address to a UID, consults the POD for the GCD owner, then retrieves the page from the corresponding PFD.</p> Signup and view all the answers

<p>GMS functions as a paging facility that stores swapped-out pages in global memory, acting as a cache similar to disk storage in traditional systems.</p> Signup and view all the answers

<p>GMS uses a variant of the Least Recently Used (LRU) algorithm, selecting the globally oldest page for replacement.</p> Signup and view all the answers

<p>Each host has local memory for the working set of processes and global memory that acts as a cache for swapped-out pages from other nodes.</p> Signup and view all the answers

<p>Host P receives page X from Host Q, increasing its local memory by one and evicting the oldest page from its global memory to maintain total memory balance.</p> Signup and view all the answers

<p>Host P must evict a page from its local memory (working set) to make room for the new page, as it cannot utilize global memory.</p> Signup and view all the answers

<p>Host P retrieves the page from disk, increasing its local memory allocation and evicting a page from global memory to maintain space.</p> Signup and view all the answers

<p>Host R must check if its globally oldest page is in global memory; if clean, it can discard it, otherwise, it must write it to disk before making room for the new page.</p> Signup and view all the answers

<p>The total physical memory on each host remains unchanged, as the swap simply reallocates pages between local and global memory.</p> Signup and view all the answers

<p>Coherence of shared pages is managed by the application and not by GMS, meaning the application is responsible for ensuring shared page consistency.</p> Signup and view all the answers

<p>The challenge lies in effectively managing the age information of pages across the cluster to accurately select the oldest page for replacement.</p> Signup and view all the answers

<p>Host P must decrease its global memory by one page to accommodate the new page, ensuring the total physical memory remains unchanged.</p> Signup and view all the answers

<p>If the globally oldest page at Host R is clean and in global memory, it can be discarded without further action.</p> Signup and view all the answers

<p>Global memory acts as a cache for pages swapped out by peers, providing a temporary storage solution for dynamically allocated resources.</p> Signup and view all the answers

<p>During standard handling, Host P's local memory increases while the global memory decreases by one page, keeping total memory constant.</p> Signup and view all the answers

<p>Dynamically managing memory allows GMS to optimize the use of cluster memory and reduce reliance on slower disk storage.</p> Signup and view all the answers