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tex/misc/w12_slices.tex

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+\documentclass{beamer}
+\usepackage[style=authortitle-comp]{biblatex}
+\usepackage[export]{adjustbox}
+
+\title{Progress Report: Page Cache Consistency Model}
+\author{Zhengyi Chen}
+\date{\today}
+
+\addbibresource{../main.bib}
+
+\begin{document}
+% Title page
+\frame{\titlepage}
+
+% Page 1
+\begin{frame}
+    \frametitle{The System}
+    \begin{itemize}
+        \item Remote node(s) abstracted as shared memory device ``\texttt{/dev/rshm}''
+        \item {
+            Heterogeneous Memory Management (HMM) ensures unified address space between
+            local and device memory.
+        }
+        \item {
+            Migration of pages between CPU and ``device'' is transparent to userspace
+            -- no need for copying/mapping.
+        }
+        \item {
+            In reality, ``\texttt{/dev/rshm}'' a handler for RDMA access between nodes.
+            \begin{itemize}
+                \item This involves remote read/write and moving page content between nodes.
+                \item Local node serves as \emph{home node \& address space host} at share time.
+                \item Remote nodes attached on \texttt{/dev/rshm} as accelerator.
+            \end{itemize}
+        }
+    \end{itemize}
+\end{frame}
+
+% Page 2
+\begin{frame}
+    \frametitle{The Problem: Consistency Protocol}
+    \begin{itemize}
+        \item Single-Writer, Multiple-Reader Protocol
+        % Why?
+        % It may be that this mimics all sorts of logic for hardware acceleration
+        % -- that is, in an HMM node each PCIe device have sole access to a page of memory.
+        % For example, during machine learning you naturally can't access the same, say,
+        % kernel by both CPU and GPU.
+        % That said, I never shed a doubt on this issue except my advisor telling me not
+        % to worry about it -- if I was asked this problem for some reason I'd be cooked!
+        \item Need to be performant\dots with some ergonomics
+        \item {
+            Two Hypothetical Protocols:
+            \begin{itemize}
+                \item ``RwLock'' Consistency Protocol
+                \item Acq-Rel Consistency Protocol
+            \end{itemize}
+        }
+        \item {
+            Former ensures \emph{strong} single-writer consistency
+            \begin{itemize}
+                \item -- Also easier to program with!
+            \end{itemize}
+        }
+        \item Latter allows concurrent in-memory \emph{non-committal} computation
+    \end{itemize}
+\end{frame}
+
+% Page 3
+\begin{frame}
+    \frametitle{``RwLock'' Consistency Protocol}
+    Similar to a read-write lock where:
+    \begin{itemize}
+        \item Multiple readers can exist for a clean page -- the page is \textbf{shared}.
+        \item Only one write is allowed for a clean page -- the page becomes \textbf{exclusive}.
+        \item {
+            For one writer node to be allowed sole write access to some page, all other
+            readers need to have their page cache invalidated.
+        }
+        \item {
+            While the sole writer node has not yet committed, no other reader or writer nodes
+            are allowed to be served this page.
+        }
+        \item {
+            When the sole writer commits, it becomes the new home node which serves the
+            updated page content.
+        }
+    \end{itemize}
+\end{frame}
+
+% Page 4
+\begin{frame}
+    \frametitle{``RwLock'' Consistency Protocol}
+    \begin{figure}
+        \centering
+        \includegraphics[width=\linewidth]{
+            w12_slides_resources/Fig-RwLockProtocol 2023-12-04 21_03_50.pdf
+        }
+    \end{figure}
+    Note: The blue arrow should be acknowledged by P3 -- forgot to put the ack. arrow in.
+\end{frame}
+
+% Page 5
+\begin{frame}
+    \frametitle{Acq-Rel Consistency Protocol}
+    In RwLock's case, read requests result in installation of read-only pages at
+    remote nodes.
+
+    Alternatively, this protocol allows read/write pages to be installed at remote
+    nodes at read time. Such writes are \emph{non-committal} and cannot be synced
+    with the entire system.
+
+    To summarize:
+    \begin{itemize}
+        \item {
+            ``Readers'' can write to its locally installed page without any means
+            to synchronize the change.
+        }
+        \item {
+            ``Writers'' need to acquire global write access from the \emph{PT node},
+            which invalidates all shared pages.
+        }
+        \item {
+            i.e., Instead of write-invalidate, perform acquire-invalidate.
+        }
+    \end{itemize}
+\end{frame}
+
+% Page 6
+\begin{frame}
+    \frametitle{Consistency Protocol: Knobs and Mods}
+    We can modify these two protocols further as follows:
+    \begin{itemize}
+        \item {
+            Multi-home Protocol: instead of having one home at a time, have
+            multiple homes (e.g., when writer commits) to prevent network bottleneck.
+        }
+        \item {
+            Auto-share: Mark pages shared via \texttt{/dev/rshm} as automatically
+            shared to some remote nodes such that 1-way communications suffice to
+            re-validate invalidated pages.
+            \begin{itemize}
+                \item Potential for communication reduction -- debatable.
+            \end{itemize}
+        }
+    \end{itemize}
+\end{frame}
+
+% Page 7
+\begin{frame}
+    \frametitle{What about Consistency \textbf{Model}?}
+    \begin{itemize}
+        \item {
+            The weaker a consistency model is, the more difficult it is to program with.
+            \begin{itemize}
+                \item {
+                    Weak ordering architectures (e.g., ARMv8) more or less depends on
+                    compiler/interpreter to emit barriers as see fit \cite{Haynes_2022}.
+                }
+                \item {
+                    Bad for usability/portability -- programs may need
+                    to be compiled using a modified toolchain, else need to add these
+                    synchronization instructions/function calls everywhere.
+                }
+            \end{itemize}
+        }
+        \item {
+            \footcite{cai2018efficient} uses Partial Store Order.
+            \begin{itemize}
+                \item Preserves RAR, WAR -- ``synchronous read\dots asynchronous write''
+                \item Easier to use than relaxed ordering.
+            \end{itemize}
+        }
+        \item {
+            \footcite{wang2021concordia} uses strong consistency, but warns about its scalability.
+        }
+    \end{itemize}
+\end{frame}
+
+% Page 8
+\begin{frame}
+    \frametitle{Consistency Model: Cont.}
+    \begin{itemize}
+        \item {
+            Similar to Concordia\footcite{wang2021concordia}, the proposed protocols also assume
+            strong consistency.
+        }
+        \item {
+            Further work needed to see how to adapt these protocols for weaker consistency models.
+        }
+    \end{itemize}
+\end{frame}
+\end{document}