Zack's Kernel News
Zack's Kernel News
Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.
Making Device-Based RAM Available To Arbitrary User Processes
Anshuman Khandual wanted to come up with a way for all attached devices to make their on-board RAM available to a running Linux system as just a normal region of RAM that any process could use without having to do anything special.
This is a tough nut to crack, because it's not just a simple matter of mapping the memory and making it available for allocation by user processes. As Anshuman put it, "To achieve seamless integration between system RAM and coherent device memory it must be able to utilize core memory kernel features like anon mapping, file mapping, page cache, driver managed pages, HW poisoning, migrations, reclaim, compaction, etc."
Each of the above requirements had its own set of difficulties, which Anshuman enumerated. For one thing, unlike regular RAM, device RAM couldn't be made available until after a given device had been initialized. That constraint would need to be handled properly. Likewise, each issue had its own constraints and caveats that would need to be papered over so that regular user code would perceive the RAM as simply being available for use.
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