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Jamie LiuandgVisor bot
41f01d8f9c
When a pages file is provided to `runsc restore`, reads from that file are asynchronous (via statefile.AsyncReader) in order to maximize throughput. However, all such reads must complete before Kernel.LoadFrom() returns, so applications cannot execute before MemoryFile loading is complete. The main objective of this CL is to allow reads to continue after Kernel.LoadFrom() returns, allowing applications to execute while MemoryFile loading is still in progress. This behavior is user-visible: it affects whether deleting the pages file frees disk space immediately on POSIX filesystems, may affect whether deletion is possible on non-POSIX filesystems, and prevents unmounting regardless. Thus it is flag-guarded as `runsc restore --background`. MemoryFile ranges that have yet to be loaded, but that are being waited-for by applications, should be prioritized over ranges for which no application is waiting. This requires that application requests for data (calls to MemoryFile.(memmap.File).DataFD/MapInternal()) are able to determine which ranges have not yet been loaded, request reads for such ranges with elevated priority, and wait for only those reads to be completed; none of these are supported by the existing statefile.AsyncReader. Thus: - Add //pkg/sentry/pgalloc/aio, which provides an async I/O API that is designed to be easily implementable using a goroutine pool, Linux native AIO, or io_uring, though only includes a goroutine pool implementation. (io_uring is widely disabled due to security vulnerabilities. In my testing, Linux native AIO is slower than the goroutine pool, but this may change with lower GOMAXPROCS which needs further testing.) - Move I/O scheduling into pgalloc: introduce an async page loader goroutine that is started by MemoryFile.LoadFrom() when async page loading is requested (implicitly, via the existence of a pages file), which is responsible for driving submission of read requests and handling their completions. PiperOrigin-RevId: 679321884