Hi,
We recently observed that
1. About half of the anonymous memory in b2g do not vary very often.
We taked a snapshot after booting into lock-screen. After playing for a
while[1], we taked the other
snapshot. The common parts of the two snapshot are around 30MB out of total
60MB anonymous memory.
2. We tried to compress the anonymous memory in b2g and the compression ratio
is 25% ~ 50%, depending on
the compression methods.
It seems that we can take advantage of these characteristics. For 1, we might
either
a. Write those anonymous memory into files and map them back after booting so
that they can be used as
page caches and OS can evict them on memory pressure.
b. Intercept mmap() to redirect all mmap(..., MAP_ANONYMOUS, ...) into files.
This is very similar to a.
c. Enable swap.
They all rely on that Linux kernel evicts clean pages first and then dirty
pages. We must tune
some parameters to strike a balance among performance, memory usage and the
life of flash.
For 2, we might enable in-kernel memory compressions[2]. For example, zRam is
an in-memory swap device that
pages are swapped in/out before/after decompression/compression, respectively.
There's no write to flash.
We might in addition add some APIs to hint kernel. For example, when an
application is lowered to
background, it is expected to be less active and becomes a good candidate to be
compressed and swapped out.
What do you think?
[1] Open facebook and twitter and look around, take a picture, run sunspider
and so on.
[2] http://lwn.net/Articles/545244/
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