> > > your memnotify check routine is written by native or java?
> >
> > Some of each.
>
> Wow!
> you have 2 /dev/mem_notify checking routine?
> java routine free java memory, native routine free native memory, right?
>
>
>
> > > my point is "on swapless system, /dev/mem_notify checked routine should be mlocked".
> >
> > mlocking didn't fix things, it just made the oom happen at a different
> > time (see graphs below), both in the small test program where I used
> > mlockall, and in the jvm where during initialization I read
> > /proc/self/maps and mlocked each region of memory that was mapped to a
> > file. Note that without swap, all of the anonymous pages containing
> > the java code are effectively locked in memory, too, so everything
> > runs without page faults.
>
> okey.
>
>
>
> > > I hope understand your requirement more.
> >
> > Most simply, I need to get low memory notifications while there is
> > still enough memory to handle them before oom.
>
> Ah, That's your implementation idea.
> I hope know why don't works well my current implementation at first.
>
>
>
> > > Can I ask your system more?
> >
> > x86, Linux 2.6.23.9 (with your patches trivially backported), 128MB,
> > no swap. Is there something else I can tell you?
> >
> > > I think all java text and data is mapped.
> >
> > It's not what /proc/meminfo calls "Mapped". It's in anonymous pages
> > with no backing store, i.e., mmap with MAP_ANONYMOUS.
>
> okey.
> Mapped of /proc/meminfo mean mapped pages with file backing store.
>
> therefore, that isn't contain anonymous memory(e.g. java).
>
>
> > > When cached+mapped+free memory is happend?
> > > and at the time, What is used memory?
> >
> > Here's a graph of MemFree, Cached, and Mapped over time (I believe
> > Mapped is mostly or entirely subset of Cached here, so it's not
> > actually important):
> >
> >
http://www.tommay.net/memory.png
>
> I hope know your system memory usage detail.
> your system have 128MB, but your graph vertical line represent 0M - 35M.
> Who use remain 93MB(128-35)?
> We should know who use memory intead decrease cached memory.
>
> So, Can you below operation before mesurement?
>
> # echo 100 > /proc/sys/vm/swappiness
> # echo 3 >/proc/sys/vm/drop_caches
>
> and, Can you mesure AnonPages of /proc/meminfo too?
> (Can your memory shrinking routine reduce anonymous memory?)
>
> if JVM use memory as anonymous memory and your memory shrinking routine can't
> anonymous memory, that isn't mem_notify proble,
> that is just poor JVM garbege collection problem.
>
> Why I think that?
> mapped page of your graph decrease linearly.
> if notification doesn't happened, it doesn't decrease.
>
> thus,
> in your system, memory notification is happend rightly.
> but your JVM doesn't have enough freeable memory.
>
> if my assumption is right, increase number of memory notification
> doesn't solve your problem.
>
> Sould we find way of good interaction to JVM GC and mem_notify shrinker?
> Sould mem_notify shrinker kick JVM GC for shrink anonymous memory?
>
>
>
>
> > My thought was to notify only when the threshold is crossed, i.e.,
> > edge-triggered not level-triggered.
>
> Hm, interesting..
>
>
>
> > But I now think a threshold
> > mechanism may be too complicated, and artificially putting pages in
> > the cache works just as well. As a proof-of-concept, I do this, and
> > it works well, but is inefficient:
> >
> > extern char _text;
> > for (int i = 0; i < bytes; i += 4096) {
> > *((volatile char *)&_text + i);
> > }
>
> you intent populate to .text segment?
> if so, you can mamp(MAP_POPULATE), IMHO.
>
>
>
> > I think embedded Java is a perfect user of /dev/mem_notify :-) I was
> > happy to see your patches and the criteria you used for notification.
> > But I'm having a problem in practice :-(
>
> Yeah, absolutely.
> I'll try to set up JVM to my test environment tomorrow.
>
>
>
