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Implementation Up: 4 Sharing Memory Previous: 4.1 Transparent
Page Sharing  4.2 Content-Based Page Sharing  Because
modifications to guest operating system internals are not
possible in our environment, and changes to application
programming interfaces are not acceptable, ESX Server takes a
completely different approach to page sharing. The basic idea is
to identify page copies by their contents. Pages with identical
contents can be shared regardless of when, where, or how those
contents were generated. This general-purpose approach has two
key advantages. First, it eliminates the need to modify, hook,
or even understand guest OS code. Second, it can identify more
opportunities for sharing; by definition, all potentially
shareable pages can be identified by their contents.  The cost
for this unobtrusive generality is that work must be performed
to scan for sharing opportunities. Clearly, comparing the
contents of each page with every other page in