Zan Lynx wrote:
I have often experienced nearly full system freezes for up to five
seconds at a time while memory is being flushed to disk.
I'm not sure if this is a general Linux problem or a Reiser4 problem, so
I thought I'd ask.
I wouldn't separate the only one of them to blame ;)
A sysrq-T during the freeze shows many processes trying to acquire a
memory page, and Reiser4 flushing atoms and doing sync things.
yup, and all processes (including interactive ones) wait for
reiser4_writepage
completion.. This takes place for mapped writes, which can not balance dirty
pages like usual writes..
My working theory right now is that Reiser4 spends time flushing a lot
of data at once before returning.
right,
there was a lightweight reaction on memory pressure notification (emergency
flush) a long time ago, but Hans couldn't live with such "swapping"
mechanism.
Also the emergency flush itself had some problems.
If I am right about that, would it not make more sense to flush a few
pages, return to the kernel, flush a few more pages, return to the
kernel, etc, etc? That way programs could get a bit of RAM and make
some progress.
I have spent 1-2 days of moving in this direction: no progress.
I wouldn't say that this is ultimately wrong way: just requires
more time to investigate..
Of course I could be completely off about what's going on.
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