Published at LXer:

On the kernel page a few weeks ago, we took a look at KSM, a technique to reduce memory usage by sharing identical pages. Currently proposed for inclusion in the mainline kernel, KSM implements a potentially useful—but not particularly new—mechanism. Unfortunately, before it can be examined on its technical merits, it may run afoul of what is essentially a political problem: software patents. The basic idea behind KSM is to find memory pages that have the same contents, then arrange for one copy to be shared amongst the various users. The kernel does some of this already for things like shared libraries, but there are numerous ways for identical pages to get created that the kernel does not know about directly, thus cannot coalesce. Examples include initialized memory (at startup or in caches) from multiple copies of the same program and virtualized guests that are running the same operating system and application programs.

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