594878 - Use /dev/ashmem for Shmem on android

Status: RESOLVED FIXED

(Core :: IPC, defect)

Description

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

android has decided not to support SysV shmem (OK) or POSIX shmem slash /dev/shm (sigh), and instead created two new shmem implementations in their kernel.  One is /dev/ashmem, which is non-physically-contiguous shmem that can be thrown out at any time when there's memory pressure (that is, just like /dev/shm except the throw-out-at-arbitrary-times bit).  It appears that mappings can be pinned, but I'm not sure that's a game we want to play.  The other is /dev/pmem, which allocates physically contiguous regions that can't be thrown out.  We don't want to touch that except for something like a video decoder.

The current android shmem implementation is mapping real files, and it's slow.  This bug covers getting us to use /dev/ashmem.  We'll need to gracefully deal with mappings being tossed out behind our back, but that's (probably) post-b1 work for a followup.

Comment 1

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

This blocks b1.

Comment 2

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

FTR, I used http://gitout.omapzoom.com/?p=kernel/common.git;a=commitdiff_plain;h=1cf25a181bf85c16a030374e6256fb078ba70ba6 to write the v0 patch.  Will be posting a cleaner v1 later today.

Comment 3

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Attachment: part 1: Factor out chromium-implemented SharedMemoryBasic in preparation for an android-specific impl

Comment 4

[Joe Drew (not getting mail)]

Comment on attachment 473895 [details] [diff] [review]
part 1: Factor out chromium-implemented SharedMemoryBasic in preparation for an android-specific impl

Nothing objectionable in here!

Comment 5

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Attachment: part 2: Add a SharedMemoryBasic impl that uses /dev/ashmem on android

Comment 6

[Michael Wu [:mwu]]

Comment on attachment 473935 [details] [diff] [review]
part 2: Add a SharedMemoryBasic impl that uses /dev/ashmem on android

How about __android_log_print for logging? strerr isn't too useful on android most of the time unless you're redirecting it to a file. See http://hg.mozilla.org/mozilla-central/file/8e2027140923/widget/src/android/AndroidJavaWrappers.h#l53 for an example.

Comment 7

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Done.

Comment 8

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

http://hg.mozilla.org/projects/cedar/rev/043bef95ecd0
http://hg.mozilla.org/projects/cedar/rev/888afabb303c