Efficient Logging in Non-Volatile Memory by Exploiting Coherency Protocols

Non-volatile memory (NVM) technologies such as PCM, ReRAM and STT-RAM allow processors to directly write values to persistent storage at speeds that are significantly faster than previous durable media such as hard drives or SSDs. Many applications of NVM are constructed on a logging subsystem, which enables operations to appear to execute atomically and facilitates recovery from failures. Writes to NVM, however, pass through a processor's memory system, which can delay and reorder them and can impair the correctness and cost of logging algorithms. Reordering arises because of out-of-order execution in a CPU and the inter-processor cache coherence protocol. By carefully considering the properties of these reorderings, this paper develops a logging protocol that requires only one round trip to non-volatile memory while avoiding expensive computations. We show how to extend the logging protocol to building a persistent set (hash map) that also requires only a single round trip to non-volatile memory for insertion, updating, or deletion

Fine-Grain Checkpointing with In-Cache-Line Logging

Non-Volatile Memory offers the possibility of implementing high-performance, durable data structures. However, achieving performance comparable to well-designed data structures in non-persistent (transient) memory is difficult, primarily because of the cost of ensuring the order in which memory writes reach NVM. Often, this requires flushing data to NVM and waiting a full memory round-trip time. In this paper, we introduce two new techniques: Fine-Grained Checkpointing, which ensures a consistent, quickly recoverable data structure in NVM after a system failure, and In-Cache-Line Logging, an undo-logging technique that enables recovery of earlier state without requiring cache-line flushes in the normal case. We implemented these techniques in the Masstree data structure, making it persistent and demonstrating the ease of applying them to a highly optimized system and their low (5.9-15.4\%) runtime overhead cost.Comment: In 2019 Architectural Support for Programming Languages and Operating Systems (ASPLOS 19), April 13, 2019, Providence, RI, US

Non-d0d^0 Mn-driven ferroelectricity in antiferromagnetic BaMnO3_3

Using first-principles density functional theory we predict a ferroelectric ground state -- driven by off-centering of the magnetic Mn$^{4+}$ ion -- in perovskite-structure BaMnO$_3$. Our finding is surprising, since the competition between energy-lowering covalent bond formation, and energy-raising Coulombic repulsions usually only favors off-centering on the perovskite $B$-site for non-magnetic $d^0$ ions. We explain this tendency for ferroelectric off-centering by analyzing the changes in electronic structure between the centrosymmetric and polar states, and by calculating the Born effective charges; we find anomalously large values for Mn and O consistent with our calculated polarization of 12.8 $\mu$C/cm$^2$. Finally, we suggest possible routes by which the perovskite phase may be stabilized over the usual hexagonal phase, to enable a practical realization of a single-phase multiferroic.Comment: 6 pages, 3 figure

k-server via multiscale entropic regularization

We present an $O((\log k)^2)$-competitive randomized algorithm for the $k$-server problem on hierarchically separated trees (HSTs). This is the first $o(k)$-competitive randomized algorithm for which the competitive ratio is independent of the size of the underlying HST. Our algorithm is designed in the framework of online mirror descent where the mirror map is a multiscale entropy. When combined with Bartal's static HST embedding reduction, this leads to an $O((\log k)^2 \log n)$-competitive algorithm on any $n$-point metric space. We give a new dynamic HST embedding that yields an $O((\log k)^3 \log \Delta)$-competitive algorithm on any metric space where the ratio of the largest to smallest non-zero distance is at most $\Delta$

Concomitant contraceptive implant and efavirenz use in women living with HIV: perspectives on current evidence and policy implications for family planning and HIV treatment guidelines.

IntroductionPreventing unintended pregnancies is important among all women, including those living with HIV. Increasing numbers of women, including HIV-positive women, choose progestin-containing subdermal implants, which are one of the most effective forms of contraception. However, drug-drug interactions between contraceptive hormones and efavirenz-based antiretroviral therapy (ART) may reduce implant effectiveness. We present four inter-related perspectives on this issue.DiscussionFirst, as a case study, we discuss how limited data prompted country-level guidance against the use of implants among women concomitantly using efavirenz in South Africa and its subsequent negative effects on the use of implants in general. Second, we discuss the existing clinical data on this topic, including the observational study from Kenya showing women using implants plus efavirenz-based ART had three-fold higher rates of pregnancy than women using implants plus nevirapine-based ART. However, the higher rates of pregnancy in the implant plus efavirenz group were still lower than the pregnancy rates among women using common alternative contraceptive methods, such as injectables. Third, we discuss the four pharmacokinetic studies that show 50-70% reductions in plasma progestin concentrations in women concurrently using efavirenz-based ART as compared to women not on any ART. These pharmacokinetic studies provide the biologic basis for the clinical findings. Fourth, we discuss how data on this topic have marked implications for both family planning and HIV programmes and policies globally.ConclusionThis controversy underlines the importance of integrating family planning services into routine HIV care, counselling women appropriately on increased risk of pregnancy with concomitant implant and efavirenz use, and expanding contraceptive method mix for all women. As global access to ART expands, greater research is needed to explore implant effectiveness when used concomitantly with newer ART regimens. Data on how HIV-positive women and their partners choose contraceptives, as well as information from providers on how they present and counsel patients on contraceptive options are needed to help guide policy and service delivery. Lastly, greater collaboration between HIV and reproductive health experts at all levels are needed to develop successful strategies to ensure the best HIV and reproductive health outcomes for women living with HIV

Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13

High-resolution optical spectra of thirteen blue horizontal-branch (BHB) stars in the globular cluster M13 show enormous deviations in element abundances from the expected cluster metallicity. In the hotter stars (T_eff > 12000 K), helium is depleted by factors of 10 to 100 below solar, while iron is enhanced to three times the solar abundance, two orders of magnitude above the canonical metallicity [Fe/H] ~= -1.5 dex for this globular cluster. Nitrogen, phosphorus, and chromium exhibit even more pronounced enhancements, and other metals are also mildly overabundant, with the exception of magnesium, which stays very near the expected cluster metallicity. These photospheric anomalies are most likely due to diffusion --- gravitational settling of helium, and radiative levitation of the other elements --- in the stable radiative atmospheres of these hot stars. The effects of these mechanisms may have some impact on the photometric morphology of the cluster's horizontal branch and on estimates of its age and distance.Comment: 11 pages, 1 Postscript figure, uses aaspp4.sty, accepted for publication in ApJ Letter