Threads of a process share address space and page tables that allows for two key advantages: 1. Amount of memory required for PTEs to map physical pages stays low even when large number of threads share the same pages since PTEs are shared across threads. 2. Page protection attributes are shared across threads and a change of attributes applies immediately to every thread without any overhead of coordinating protection bit changes across threads. These advantages no longer apply when unrelated processes share pages. Large database applications can easily comprise of 1000s of processes that share 100s of GB of pages. In cases like this, amount of memory consumed by page tables can exceed the size of actual shared data. On a database server with 300GB SGA, a system crash was seen with out-of-memory condition when 1500+ clients tried to share this SGA even though the system had 512GB of memory. On this server, in the worst case scenario of all 1500 processes mapping every page from SGA would have required 878GB+ for just the PTEs. I have sent proposals and patches to solve this problem by adding a mechanism to the kernel for processes to use to opt into sharing page tables with other processes. We have had discussions on original proposal and subsequent refinements but we have not converged on a solution. As systems with multi-TB memory and in-memory databases are becoming more and more common, this is becoming a significant issue. An interactive discussion can help us reach a consensus on how to solve this. Thanks, Khalid References: https://lore.kernel.org/lkml/cover.1642526745.git.khalid.aziz@xxxxxxxxxx/ https://lore.kernel.org/lkml/cover.1656531090.git.khalid.aziz@xxxxxxxxxx/ https://lore.kernel.org/lkml/cover.1682453344.git.khalid.aziz@xxxxxxxxxx/ https://lore.kernel.org/lkml/4082bc40-a99a-4b54-91e5-a1b55828d202@xxxxxxxxxx/
