A Non-blocking Buddy System for Scalable Memory Allocation on Multi-core Machines

Common implementations of core memory allocation components handle concurrent allocation/release requests by synchronizing threads via spin-locks. This approach is not prone to scale with large thread counts, a problem that has been addressed in the literature by introducing layered allocation services or replicating the core allocators - the bottom most ones within the layered architecture. Both these solutions tend to reduce the pressure of actual concurrent accesses to each individual core allocator. In this article we explore an alternative approach to scalability of memory allocation/release, which can be still combined with those literature proposals. We present a fully non-blocking buddy-system, that allows threads to proceed in parallel, and commit their allocations/releases unless a conflict is materialized while handling its metadata. Beyond improving scalability and performance it is resilient to performance degradation in face of concurrent accesses independently of the current level of fragmentation of the handled memory blocks

NBBS: A Non-blocking Buddy System for Multi-core Machines

Common implementations of core memory allocation components, like the Linux buddy system, handle concurrent allocation/release requests by synchronizing threads via spinlocks. This approach is not prone to scale with large thread counts, a problem that has been addressed in the literature by introducing layered allocation services or replicating the core allocators—the bottom most ones within the layered architecture. Both these solutions tend to reduce the pressure of actual concurrent accesses to each individual core allocator. In this article we explore an alternative approach to scalability of memory allocation/release, which can be still combined with those literature proposals. We present a fully non-blocking buddy-system, where threads performing concurrent allocations/releases do not undergo any spinlock based synchronization. Our solution allows threads to proceed in parallel, and commit their allocations/releases unless a conflict is materialized while handling its metadata. Conflict detection relies on conventional atomic machine instructions in the Read-Modify-Write (RMW) class. Beyond improving scalability and performance, our solution can also avoid wasting clock cycles for spin-lock operations by threads that could in principle carry out their memory allocation/release in full concurrency. Thus, it is resilient to performance degradation—in face of concurrent accesses—independently of the current level of fragmentation of the handled memory blocks

A Non-blocking Buddy System for Scalable Memory Allocation on Multi-core Machines

Common implementations of core memory allocation components, like the Linux buddy system, handle concurrent allocation/release requests by synchronizing threads via spin-locks. This approach is clearly not prone to scale with large thread counts, a problem that has been addressed in the literature by introducing layered allocation services or replicating the core allocators-the bottom most ones within the layered architecture. Both these solutions tend to reduce the pressure of actual concurrent accesses to each individual core allocator. In this article we explore an alternative approach to scalability of memory allocation/release, which can be still combined with those literature proposals. Conflict detection relies on conventional atomic machine instructions in the Read-Modify-Write (RMW) class. Furthermore, beyond improving scalability and performance, it can also avoid wasting clock cycles for spin-lock operations by threads that could in principle carry out their memory allocation/release in full concurrency. Thus, it is resilient to performance degradation---in face of concurrent accesses---independently of the current level of fragmentation of the handled memory blocks

Cutaneous granulomatosis and combined immunodeficiency revealing Ataxia-Telangiectasia: a case report

Ataxia-telangiectasia (A-T) is a complex multisystem disorder characterized by progressive neurological impairment, variable immunodeficiency and oculo-cutaneous telangiectasia. A-T is a member of chromosomal breakage syndromes and it is caused by a mutation in the ataxia-telangiectasia mutated (ATM) gene. Because of a wide clinical heterogeneity, A-T is often difficult to diagnose in children

Preeclampsia in Lean Normotensive Normotolerant Pregnant Women Can Be Predicted by Simple Insulin Sensitivity Indexes

Certain similarities between preeclampsia and insulin resistance syndrome suggest a possible link between the 2 diseases. The aim of our study was to evaluate 3 insulin sensitivity (IS) indexes (fasting homeostasis model assessment IS [IS HOMA ], quantitative insulin sensitivity check index [IS QUICKI ], and oral glucose IS [OGIS]) early and late in pregnancy in a large number of normotensive pregnant women with a normal glucose tolerance and to test the ability of these indexes to predict the risk of subsequent preeclampsia. In all, 829 pregnant women were tested with a 75-g, 2-hour oral glucose load in 2 periods of pregnancy: early (16 to 20 weeks) and late (26 to 30 weeks). In early and late pregnancy, respectively, IS HOMA was 1.23±0.05 and 1.44±0.05 ( P <0.01), IS QUICKI was 0.40±0.002 and 0.38±0.002 ( P <0.01), and OGIS was 457±2.4 mL min −1 m −2 and 445±2.2 ( P <0.001), all confirming the reduction in insulin sensitivity during pregnancy. Preeclampsia developed in 6.4% of the pregnant women and correlated positively with the 75th centile of IS HOMA ( P =0.001), with a sensitivity of 79% in the early and 83% in the late period and a specificity of 97% in both. IS QUICKI <25th centile was also related with preeclampsia ( P =0.001), with a sensitivity of 85% in the early and 88% in the late period and a specificity of 97% in both. Judging from our findings, IS HOMA and IS QUICKI are simple tests that can pinpoint impaired insulin sensitivity early in the pregnancy. Given their high sensitivity and specificity, these indexes could be useful in predicting the development of preeclampsia in early pregnancy, before the disease become clinically evident

Nonlinear Elastic Tomography using sparse array measurements

Literature offers a quantitative number of diagnostic imaging methods that can continuously provide a detailed image of the material defects in aerospace and civil applications. This paper presents a nonlinear Structural Health Monitoring (SHM) imaging method, based on nonlinear elastic wave tomography (NEWT), for the detection of the nonlinear signature in damaged isotropic structures. The proposed technique, based on a combination of higher order statistics (HOS) and radial basis function (RBF) interpolation, is applied to a number of waveforms containing the nonlinear responses of the medium. HOS such as bispectral analysis and bicoherence was used to characterize the second order nonlinearity of the structure due to corrosion, whilst RBF interpolation was applied to a number of signals acquired from a sparse array of sensors, in order to obtain an image of the defect. Compared to standard linear ultrasonic imaging techniques, the robustness of this nonlinear tomography sensing system was experimentally demonstrated. Moreover, this methodology does not require any baseline with the undamaged structure for the detection of the nonlinear source as well as a priori knowledge of the mechanical properties of the medium. Finally, the use of HOS makes NEWT a valid alternative to traditional nonlinear elastic wave spectroscopy (NEWS) methods for materials showing either classical or non-classical nonlinear behaviour