On 11/21/2012 04:36 PM, John Stultz wrote:
2) Being able to use this with tmpfs files. I'm currently trying to
better understand the rmap code, looking to see if there's a way to
have try_to_unmap_file() work similarly to try_to_unmap_anon(), to
allow allow users to madvise() on mmapped tmpfs files. This would
provide a very similar interface as to what I've been proposing with
fadvise/fallocate, but just using process virtual addresses instead of
(fd, offset) pairs. The benefit with (fd,offset) pairs for Android
is that its easier to manage shared volatile ranges between two
processes that are sharing data via an mmapped tmpfs file (although
this actual use case may be fairly rare). I believe we should still
be able to rework the ashmem internals to use madvise (which would
provide legacy support for existing android apps), so then its just a
question of if we could then eventually convince Android apps to use
the madvise interface directly, rather then the ashmem unpin ioctl.
Hey Minchan,
I've been playing around with your patch trying to better
understand your approach and to extend it to support tmpfs files. In
doing so I've found a few bugs, and have some rough fixes I wanted to
share. There's still a few edge cases I need to deal with (the
vma-purged flag isn't being properly handled through vma merge/split
operations), but its starting to come along.
Anyway, take a look at the tree here and let me know what you think.
http://git.linaro.org/gitweb?p=people/jstultz/android-dev.git;a=shortlog;h=refs/heads/dev/minchan-anonvol
I'm sure much is wrong with the tree, but with it I can now mark tmpfs
file pages as volatile/nonvolatile and see them purged under pressure.
Unfortunately its not limited to tmpfs, so persistent files will also
work, but the state of the underlying files on purge is undefined.
Hopefully I can find a way to limit it to non-persistent filesystems for
now, and if needed find a way to extend it to persistent filesystems in
a sane way later.
thanks
-john
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