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AshMem

Anonymous SHared Memory

originally an Android facility to allow more reclaim opportunities in swapless systems.

Use Cases

  • Large application needs to cache expensive operations. But, these operations are _less_ expensive than swapping and less expensive than if the app got, for instance, OOM-killed. The Android browser uses this to store decompressed images so it can draw them to the screen. It can always decompress them again, and a swapped-out decompressed image is pretty worthless.

  • Producer -> Consumer Model :

  • Intermittent Use. Generally smaller applications that run only occasionally, and not for long periods of time.

    • Obviously contrived example: "grep" could keep the results of a grep through a large file in an ashmem cache. If you did the same grep twice, you could return the cached result instead of reading the large file again.

    • This kind of use does not fit well with a model where VMAs are used to track volatility. There generally is not a VMA around since the program only runs for a short time. If a VMA would be required to indicate the reclaim state of a page, then it could not be reclaimed most of the time.

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last edited 2012-10-09 14:49:06 by DaveHansen