On Mon, 18 Jul 2011, John Stultz wrote:

> Additionally, ashmem introduces the concept of page pinning. Pinned pages (the
> default) behave like any anonymous memory. Unpinned pages are available to the
> kernel for eviction during VM pressure. When repinning the pages, the return
> value instructs user-space as to any eviction. In this manner, user-space
> processes may implement caching and similar resource management that
> efficiently integrates with kernel memory management.

Memory locking (mlock) may be a better term to use here. mlock prevents
eviction. Page pinning also prevents the movement of the pages in memory
(as needed by page migration, compaction etc).