I don’t think these two issues require to be solved together, although I agree
there is some connection.
I guess we agree that pre-touch should a be off by default.
Similarly, lazy data region initialization from IGNITE-9113 can be on by
default.
We can have two boolean properties controlling each feature, e.g.
IGNITE_EAGER_DATA_REGION_INITIALIZATION
IGNITE_PRE_TOUCH_OFF_HEAP_MEMORY
Setting both to true will make sure that all memory is committed as early as
possible.
Different combinations will allow for all 4 variants you’ve mentioned. I can
see a use case for each one:
- lazy region init + no pre-touch (default) – easier configuration (at least
for simple use cases without a lot of regions and node filters) and faster
startup
- lazy region init + pre-touch – allows to reuse server config on a client (the
goal of the IGNITE-9113) but still allows to fail-fast on cache creation
- eager region init + no pre-touch – for cases when you want to eagerly
allocate memory but don’t care about committing physical pages; e.g. if you
have overcommit disabled then you don’t need to pre-touch everything to make
sure the memory is there
- eager region init + pre-touch – to fail as early as possible if there is not
enough RAM
Stan
From: Nikolay Izhikov
Sent: 14 декабря 2018 г. 14:42
To: dev; vololo...@gmail.com; stanlukya...@gmail.com
Subject: Re: Pre-touch for Ignite off-heap memory
Bump.
Stanislav, Ivan, can you answer my questions?
Let's discuss these improvements.
ср, 12 дек. 2018 г. в 22:14, Павлухин Иван <vololo...@gmail.com>:
> Hi Stan,
>
> As I participated in discussion in current thread I would like to
> leave a comment.
>
> Your concerns looks clear for me and if you believe that pre-touch
> will help product users then I have nothing against it.
> ср, 12 дек. 2018 г. в 11:09, Nikolay Izhikov <nizhi...@apache.org>:
> >
> > Hello, Stanislav.
> >
> > As far as I can see, we have controversal ticket based on previous
> dev-list discussion:
> >
> > IGNITE-9113 - Allocate memory for a data region when first cache
> assigned to this region is created [1]
> >
> > I planned to implement it soon.
> > Looks like we should have several options of memory(data regions)
> allocation:
> >
> > - allocate all on startup (AFAIK this is how current
> implementation behave)
> > - allocate all on startup AND pre touch.
> > - allocate specific data region for first assignment.
> > - allocate specific data region for first assignment AND pre
> touch.
> >
> > What do you think?
> >
> > [1] https://issues.apache.org/jira/browse/IGNITE-9113
> >
> > В Вт, 11/12/2018 в 19:39 +0300, Stanislav Lukyanov пишет:
> > > Igniters,
> > >
> > > What is being suggested here is an Ignite off-heap’s version of Java’s
> -XX:+AlwaysPreTouch.
> > > The latter is known to be used to guarantee that the committed memory
> is backed by physical RAM.
> > > This ensures that
> > > a) JVM doesn’t have to do it during the actual work (avoiding overhead
> for physical page allocation, possible contention with page cache, etc)
> > > b) JVM fails fast if the Xmx is greater than available RAM
> > > c) New processes will not be able to claim the memory JVM took for
> itself
> > >
> > > Currently one can’t get the same benefits for Ignite because we use
> off-heap as well as heap.
> > > So, we can implement a similar feature for Ignite – and make sure the
> users can get all the memory pre-touch benefits if they want.
> > > Of course, it impacts startup time so we should enable it by a
> configuration property (I’d suggest a system property for now).
> > >
> > > Are there any objections to implementing this?
> > >
> > > Thanks,
> > > Stan
> > >
> > > From: Павлухин Иван
> > > Sent: 31 октября 2018 г. 12:50
> > > To: dev@ignite.apache.org
> > > Subject: Re: Pre-touch for Ignite off-heap memory
> > >
> > > Hi,
> > >
> > > I did an experiment described above. I created a patch with pre-touch
> [1]
> > > and started a JVM with an option -XX:+AlwaysPreTouch and configured
> > > Ignite with equal values for initial and max sizes for each data
> region.
> > > I did several runs. I observed JVM crash dumps [2], [3]. Also it is
> easy
> > > to observe JVM OOM-killed.
> > >
> > > [1] https://github.com/apache/ignite/pull/5220
> > > [2]
> > >
> https://gist.github.com/pavlukhin/e5e6605e9b43666266667ba8d1aab42f#file-hs_err_pid5763-log
> > > [3]
> > >
> https://gist.github.com/pavlukhin/e5e6605e9b43666266667ba8d1aab42f#file-hs_err_pid6411-log
> > >
> > > вт, 30 окт. 2018 г. в 9:19, Павлухин Иван <vololo...@gmail.com>:
> > >
> > > > Hi guys,
> > > >
> > > > I am not aware that it is possible to run JVM in "allocation-free"
> fashion.
> > > > If you know that it is possible please share it. As I know JVM
> allocates
> > > > memory out of garbage collectable area for internal purposes like
> JIT,
> > > > GC itself. Also native built-it code can request memory allocation
> from OS,
> > > > e.g. zip facilities. If we imagine that system is running under
> memory
> > > > allocation
> > > > which is close to a limit then even small allocation request can
> fail and
> > > > lead
> > > > to OOM killing.
> > > >
> > > > But I think that a simple and useful thing that could be done first
> is
> > > > making
> > > > an experiment. As Andrey mentioned
> > > > > AFAIK, Ignite always pre-touch first region. So, you can try to set
> > > >
> > > > region
> > > > > MAX size equal to MIN and get region allocated on node start.
> > > >
> > > > If it is so then it should not be hard to launch Ignite and observe
> it
> > > > running
> > > > very close to OS memory limit with Java heap and Ignite off-heap
> > > > pre-touched.
> > > > After that one could check whether it is possible to observe Ignite
> OOM
> > > > killed.
> > > > Let's say my bet is that it is relatively easy to catch OOM here.
> > > >
> > > > What do you think?
> > > >
> > > > пт, 26 окт. 2018 г. в 18:18, Yakov Zhdanov <yzhda...@apache.org>:
> > > >
> > > > > Andrey,
> > > > >
> > > > > Probability of a OOM kill will be much lower if offheap is
> pretouched.
> > > > > What
> > > > > do you mean by JVM internal needs? In my understanding if user
> enables
> > > > > option to pretouch heap and fixes the heap to prevent jvm
> releasing memory
> > > > > back to OS, then OOM killing is very unlikely.
> > > > >
> > > > > I would agree that pretouch for offheap may be helpful in many
> cases.
> > > > >
> > > > > --Yakov
> > > > >
> > > >
> > > >
> > > > --
> > > > Best regards,
> > > > Ivan Pavlukhin
> > > >
> > >
> > >
>
>
>
> --
> Best regards,
> Ivan Pavlukhin
>
