A new compression model, called CRAM, offers a different path to compression that avoids swap entirely by keeping the compressed data in memory, and it offers up to 452x the performance of ZRAM. I was a kid in the 1990s when the idea seemed so simple to me: I can use PKZIP to compress my files, so why can't we do that with RAM? Indeed, I am not a singular genius, and many other people had the same idea, so memory compression has been a feature of most operating systems for a long time. In Linux, the most popular options are zswap and ZRAM, but both of these options are fundamentally swap-layer features. CRAM is a new take that claims to boost performance tremendously.

CRAM was conceptualized by Gregory Price and his team at Meta. The central realization that seems to have spurred the development of CRAM is that the largest portion of the performance hit from compressed memory isn't the compression; that's tiny. No, the largest hit apparently stems mostly from the fault itself and the swap behavior. So the thinking seems to have been "what if we just do zram, but completely in memory instead of as swap?"

That's a gross simplification of an enormously complex project , but what CRAM seems to be doing is making use of mechanisms Linux already has to enable radically higher-performance compressed memory, particularly on reads. It uses a private NUMA node (essentially, a ghost CPU) instead of pretending to be a block device, and this lets Linux continue using all of its memory semantics, including migration and ballooning, to manage CRAM.

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