Red Hat, Inc.

Red Hat Israel, Ltd.

Christopher M Wright

Michael Tsirkin

Andrea Arcangeli

Izik Eidus

A method and system for managing direct memory access (DMA) in a computer system without a host input/output memory management unit (IOMMU). The computer system hosts virtual machines and allows memory overcommit. The computer receives, from a guest operating system that runs on a virtual machine, a request for mapping a guest address to a bus address. The computer translates the guest address to a host address and pins a memory page containing the host address to keep the memory page in host memory. The host address is then returned to the guest operating system to allow a device to use the host address as the bus address for direct memory access (DMA) to a buffer managed by the guest operating system.

Memory overcommit by using an emulated IOMMU in a computer system without a host IOMMU

A system and method for memory sharing among computer programs is disclosed. A method for memory sharing among computer programs includes identifying memory units of a plurality of memory units having identical contents, collapsing the identified memory units into a single merged memory page, and mapping the single merged memory page into an associated shared physical memory location. The method further includes when a request to write to a memory unit merged into the single merged memory page is received: copying, by a computer system, contents in the associated shared physical memory location to a different memory location, and redirecting, by the computer system, the request to the different memory location.

Memory sharing among computer programs

A method and system for managing direct memory access (DMA) in a computer system that hosts virtual machines and allows memory overcommit. The computer receives an indication that a bus address is to be used by a device to perform DMA to a buffer. In response to the indication, the computer determines a host device identifier for the device, and pins a memory page addressed by a host address that is associated with the bus address and a guest address. The computer also records, in a host I/O memory management unit (IOMMU), a mapping of the bus address and the host device identifier to the host address. After the device completes the DMA, the computer removes the mapping from the host IOMMU to prevent further direct access to the host address.

Memory overcommit by using an emulated IOMMU in a computer system with a host IOMMU

A physical memory location among multiple programs is shared among multiple programs. In one embodiment, multiple memory units are scanned to detect duplicated contents in the memory units. The memory units are used by programs running on a computer system. A data structure is used to identify memory units of identical contents. To improve performance, an additional data structure can be used to identify memory units of identical contents. Memory units that are identified to have identical contents can share the same physical memory space.

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Portland, OR, United States of America

Christopher M Wright