Red Hat OpenShift offers horizontal pod autoscaling (HPA) primarily for CPUs, but it can also perform memory-based HPA, which is useful for applications that are more memory-intensive than CPU-intensive. In this article, I demonstrate how to use OpenShift’s memory-based horizontal pod autoscaling feature (tech preview) to autoscale your pods if the demands on memory increase. The test performed in this article might not necessarily reflect a real application. The tests only aim to demonstrate memory-based HPA in the simplest way possible.
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Continuing in the effort to detect common programming errors, the just-released GCC 8 contains a number of new warnings as well as enhancements to existing checkers to help find non-obvious bugs in C and C++ code. This article focuses on those that deal with inadvertent string truncation and discusses some of the approaches for avoiding the underlying problems. If you haven’t read it, you might also want to read David Malcolm’s article Usability improvements in GCC 8.
To use GCC 8 on RHEL, see How to install GCC 8 and Clang/LLVM 6 on Red Hat Enterprise Linux 7. GCC 8 is the default compiler in Red Hat Enterprise Linux 8 Beta.
Why Is String Truncation a Problem?
It is well-known why buffer overflow is dangerous: writing past the end of an object can overwrite data in adjacent storage, resulting in data corruption. In the most benign cases, the corruption can simply lead to incorrect behavior of the program. If the adjacent data is an address in the executable text segment, the corruption may be exploitable to gain control of the affected process, which can lead to a security vulnerability. (See CWE-119 for more on buffer overflow.)
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GCC has a rich set of features designed to help detect many kinds of programming errors. Of particular interest are those that corrupt the memory of a running program and, in some cases, makes it vulnerable to security threats. Since 2006, GCC has provided a solution to detect and prevent a subset of buffer overflows in C and C++ programs. Although it is based on compiler technology, it’s best known under the name Fortify Source derived from the synonymous GNU C Library macro that controls the feature: _FORTIFY_SOURCE. GCC has changed and improved considerably since its 4.1 release in 2006, and with its ability to detect these sorts of errors. GCC 7, in particular, contains a number of enhancements that help detect several new kinds of programming errors in this area. This article provides a brief overview of these new features. For a comprehensive list of all major improvements in GCC 7, please see GCC 7 Changes document.
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Do you have a Java application that runs fine at first but slows down after a while, or it runs fine for a small number of files but performance degrades for large number of files? Maybe you have a memory leak.
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All modern processors use page-based mechanisms to translate the user-space processes virtual addresses into physical addresses for RAM. The pages are commonly 4KB in size and the processor can hold a limited number of virtual-to-physical address mappings in the Translation Lookaside Buffers (TLB). The number TLB entries ranges from tens to hundreds of mappings. This limits a processor to a few
megabytes of memory it can address without changing the TLB entries. When a virtual-to-physical address mapping is not in the TLB the processor must do an expensive computation to generate a new virtual-to-physical address mapping.
Continue reading “Examining Huge Pages or Transparent Huge Pages performance”