...

tex/misc/background_draft.bib

@@ -281,5 +281,45 @@
   organization={IEEE}
 }
 
+@book{AST_Steen.Distributed_Systems-3ed.2017,
+  title={Distributed systems},
+  author={Van Steen, Maarten and Tanenbaum, Andrew S},
+  year={2017},
+  publisher={Maarten van Steen Leiden, The Netherlands}
+}
 
+@article{De_Wael_etal.PGAS_Survey.2015,
+  title={Partitioned global address space languages},
+  author={De Wael, Mattias and Marr, Stefan and De Fraine, Bruno and Van Cutsem, Tom and De Meuter, Wolfgang},
+  journal={ACM Computing Surveys (CSUR)},
+  volume={47},
+  number={4},
+  pages={1--27},
+  year={2015},
+  publisher={ACM New York, NY, USA}
+}
+
+@misc{WEB.HPE.Chapel_Platforms-v1.33.2023,
+  title={Platform-Specifc Notes},
+  url={https://chapel-lang.org/docs/platforms/index.html#},
+  journal={Chapel Documentation 1.33},
+  publisher={Hewlett Packard Enterprise Development LP.},
+  year={2023}
+}
+
+@misc{WEB.LBNL.UPC_man_1_upcc.2022,
+  title={upcc.1},
+  url={https://upc.lbl.gov/docs/user/upcc.html},
+  journal={Manual Reference Pages - UPCC (1)},
+  publisher={Lawrence Berkeley National Laboratory},
+  year={2022}
+}
+
+@inproceedings{Zhou_etal.DART-MPI.2014,
+  title={DART-MPI: An MPI-based implementation of a PGAS runtime system},
+  author={Zhou, Huan and Mhedheb, Yousri and Idrees, Kamran and Glass, Colin W and Gracia, Jos{\'e} and F{\"u}rlinger, Karl},
+  booktitle={Proceedings of the 8th International Conference on Partitioned Global Address Space Programming Models},
+  pages={1--11},
+  year={2014}
+}
 

tex/misc/background_draft.tex

@@ -214,10 +214,75 @@ DSM systems are at least as viable as traditional PGAS/message-passing framework
 for scientific computing, also corroborated by the resurgence of DSM studies
 later on\cite{Masouros_etal.Adrias.2023}.
 
-\section{HPC and Partitioned Global Address Space}
+\section{PGAS and Message Passing}
-Improvement in NIC bandwidth and transfer rate allows for applications that expose
+While the feasibility of transparent DSM systems over multiple machines on the
-global address space, as well as RDMA technologies that leverage single-writer
+network has been made apparent since the 1980s, predominant approaches to
-protocols over hierarchical memory nodes. \textbf{[GAS and PGAS (Partitioned GAS)
+``scaling-out'' programs over the network relies on the message-passing approach
+\cite{AST_Steen.Distributed_Systems-3ed.2017}. The reasons are twofold:
+
+\begin{enumerate}
+    \item {
+        Programmers would rather resort to more intricate, more predictable
+        approaches to scaling-out programs over the network
+        \cite{AST_Steen.Distributed_Systems-3ed.2017}. This implies
+        manual/controlled data sharding over nodes, separation of compute and
+        communication ``stages'' of computation, etc., which benefit performance
+        analysis.
+    }
+    \item {
+        Enterprise applications value throughput and uptime of relatively
+        computationally inexpensive tasks/resources
+        \cite{BOOK.Hennessy_Patterson.CArch.2011}, which requires easy
+        scalability of tried-and-true, latency-inexpensive applications.
+        Studies in transparent DSM systems mostly require exotic,
+        specifically-written programs to exploit global address space, which is
+        fundamentally at odds in terms of reusability and flexibility required.
+    }
+\end{enumerate}
+
+\subsection{PGAS}
+\textit{Partitioned Global Address Space} (PGAS) is a parallel programming model
+that (1) exposes a global address space to all machines within a network and
+(2) explicates distinction between local and remote memory
+\cite{De_Wael_etal.PGAS_Survey.2015}. Oftentimes, message-passing frameworks,
+for example \textit{OpenMPI}, \textit{OpenFabrics}, and \textit{UCX}, are used
+as backends to provide the PGAS model over various network interfaces/platforms
+(e.g., Ethernet and Infiniband)\cites{WEB.LBNL.UPC_man_1_upcc.2022}
+{WEB.HPE.Chapel_Platforms-v1.33.2023}.
+
+Examples of PGAS programming languages and models include \textcolor{red}{\dots}.
+Notably, implementation of a \emph{global} address space across machines on top
+of machines already equipped with their own \emph{local} address space (e.g.,
+cluster nodes running commercial Linux) necessitates a global addressing
+mechanism for shared/shared data objects. DART\cite{Zhou_etal.DART-MPI.2014},
+for example, utilizes a 128-bit ``global pointer'' to encode global memory
+object/segment ID and access flags in the upper 64 bits and virtual addresses in
+the lower 64 bits for each (slice of) memory object allocated within the PGAS
+model. A \textit{non-collective} PGAS object is allocated entirely local to the
+allocating node's memory, but registered globally. Consequently, a single global
+pointer is recorded in the runtime with corresponding permission flags for the
+context of some user-defined group of associated nodes. Comparatively, a
+\textit{collective} PGAS object is allocated such that a partition of the object
+(i.e., a subarray of the repr) is stored in each of the associated node -- for
+a $k$-partitioned object, $k$ global pointers are recorded in the runtime each
+pointing to the same object, with different offsets and (naturally)
+independently-chosen virtual addresses. Note that this design naturally requires
+virtual addresses within each node to be \emph{pinned} -- the allocated object
+cannot be re-addressed to a different virtual address i.e., the global pointer
+that records the local virtual address cannot be auto-invalidated.
+
+Similar schemes can be observed in other PGAS backends/runtimes, albeit they may
+opt to use a map-like data structure for addressing instead. In general, PGAS
+backends differ from DSM systems in that, despite providing memory management
+over remote nodes, they provide no transparent caching and transfer of remote
+memory objects accessed by local nodes. The programmer is still expected to
+handle data/thread movement manually when working with shared memory over network
+to maximize performance metrics of interest.
+
+\dots
+
+Improvement in NIC bandwidth and transfer rate benefits DSM applications that expose
+global address space, and those that leverage single-writer capabilities over hierarchical memory nodes. \textbf{[GAS and PGAS (Partitioned GAS)
 technologies for example Openshmem, OpenMPI, Cray Chapel, etc. that leverage
 specially-linked memory sections and \texttt{/dev/shm} to abstract away RDMA access]}.