I think Till has a good point. The default should work well, because very few users will ever change it. Even on OOMs. So I am slightly in favor of going with jemalloc.
@Yun Tang - Do you see a noticeable performance difference between the two? On Thu, Oct 29, 2020 at 12:32 PM Yun Tang <myas...@live.com> wrote: > Hi > > I think Till's view deserves wider discussion. > I want to give my two cents when I debug with Nico on his reported RocksDB > OOM problem. > Jemalloc has the mechanism to profile memory allocation [1] which is > widely used to analysis memory leak. > Once we set jemalloc as default memory allocator, the frequency of OOM > behavior decreases obviously. > > Considering the OOM killed problem in k8s, change default memory allocator > as jemalloc could be something beneficial. > > [1] https://github.com/jemalloc/jemalloc/wiki/Use-Case%3A-Heap-Profiling > > Best > Yun Tang > > ________________________________ > From: Till Rohrmann <trohrm...@apache.org> > Sent: Thursday, October 29, 2020 18:34 > To: dev <dev@flink.apache.org> > Cc: Yun Tang <myas...@live.com> > Subject: Re: [DISCUSS][docker] Adopt Jemalloc as default memory allocator > for debian based Flink docker image > > Hi Yu, > > I see your point why you are in favour of continuing using glibc. > > I honestly don't have a lot of experience with malloc libraries so I can > only argue from a general perspective: We know that glibc has some problems > wrt to memory fragmentation which can cause processes to exceed its memory > limit. jemalloc seems to address this problem by avoiding memory > fragmentation. However, it might be the case that jemalloc introduces other > problems. In order to figure this out we would need to collect more data > points/experience. So in the end we have to weigh glibc memory > fragmentation against unknown problems in jemalloc. > > Given that choosing the malloc library will be quite an expert setting, I > don't expect many Flink users to use it in case they see OOMs. Hence, I > would be slightly in favour of choosing jemalloc as the default because it > would allow us to gather feedback from users and solve the existing > problem. In the best case, user's won't run into new problems. If they do, > then we will have to re-evaluate this decision and might have to switch the > malloc library back. W/o setting jemalloc as the default, I fear that we > will never gather enough feedback to make jemalloc confidently the default. > > What one could argue, though, is that making jemalloc the default so > shortly before the feature freeze limits the timespan we can observe how it > behaves before the actual release. Doing such a change at the beginning of > a release cycle, would allow us to gain more confidence. > > In any way, I believe that we should add a big release note and document > what users should do in case they see memory issues (OOM kills, slower > performance, etc.). > > Cheers, > Till > > On Tue, Oct 20, 2020 at 5:39 PM Yu Li <car...@gmail.com> wrote: > > > True, thanks for the reminder Till! > > > > I suggest using glibc malloc as default. On one hand this follows our old > > behavior (only with glibc malloc support in the image), on the other > hand I > > believe glibc isn't using jemalloc as its default memory allocator for > some > > reason. > > > > Please let me know your thoughts. Thanks. > > > > Best Regards, > > Yu > > > > > > On Tue, 20 Oct 2020 at 21:45, Till Rohrmann <trohrm...@apache.org> > wrote: > > > > > The only question left would be what will be the default value? > > > > > > Cheers, > > > Till > > > > > > On Tue, Oct 20, 2020 at 10:16 AM Yu Li <car...@gmail.com> wrote: > > > > > > > I'm also +1 on making it configurable in the same Docker image. > > > > > > > > It seems we have reached consensus and there are already enough +1s > to > > > move > > > > forward, and suggest @Yun to conclude the discussion directly if > there > > > are > > > > no objections. > > > > > > > > Thanks. > > > > > > > > Best Regards, > > > > Yu > > > > > > > > > > > > On Fri, 16 Oct 2020 at 23:16, Till Rohrmann <trohrm...@apache.org> > > > wrote: > > > > > > > > > +1 for making it configurable in the same Docker image. > > > > > > > > > > Cheers, > > > > > Till > > > > > > > > > > On Fri, Oct 16, 2020 at 12:56 PM Chesnay Schepler < > > ches...@apache.org> > > > > > wrote: > > > > > > > > > > > If it is possible to support both allocators in a single image > then > > > we > > > > > > should definitely go with that option. > > > > > > > > > > > > On 10/16/2020 12:21 PM, Yun Tang wrote: > > > > > > > Thanks for Yang's suggestion. I think this could be a better > > > choice. > > > > > > > We could install jemalloc and only enable it in LD_PRELOAD when > > > user > > > > > > pass specific configuration for docker-entrypoint.sh. > > > > > > > By doing so, we could avoid to create another docker image tags > > and > > > > > also > > > > > > offer ability to reduce memory fragmentation problem. > > > > > > > > > > > > > > Does anyone else have other ideas? > > > > > > > > > > > > > > Best > > > > > > > Yun Tang > > > > > > > ________________________________ > > > > > > > From: Yang Wang <danrtsey...@gmail.com> > > > > > > > Sent: Thursday, October 15, 2020 14:59 > > > > > > > To: dev <dev@flink.apache.org> > > > > > > > Subject: Re: [DISCUSS][docker] Adopt Jemalloc as default memory > > > > > > allocator for debian based Flink docker image > > > > > > > > > > > > > > Thanks Yun Tang for starting this discussion. > > > > > > > > > > > > > > I think this is very important when deploy Flink with container > > > > > > environment > > > > > > > in production. I just > > > > > > > have quick question. Could we have both memory allocator(e.g. > > > glibc, > > > > > > > jemalloc) in the Flink > > > > > > > official image and enable a specific one by setting ENV? > > > > > > > > > > > > > > Best, > > > > > > > Yang > > > > > > > > > > > > > > Yu Li <car...@gmail.com> 于2020年10月14日周三 下午12:23写道： > > > > > > > > > > > > > >> Thanks for debugging and resolving the issue and driving the > > > > > discussion > > > > > > >> Yun! > > > > > > >> > > > > > > >> For the given solutions, I prefer option 1 (supply another > > > > Dockerfile > > > > > > using > > > > > > >> jemalloc as default memory allocator) because of the below > > > reasons: > > > > > > >> > > > > > > >> 1. It's hard to say jemalloc is always better than ptmalloc > > (glibc > > > > > > malloc), > > > > > > >> or else glibc should have already adopted it as the default > > memory > > > > > > >> allocator. And as indicated here [1], in some cases jemalloc > > will > > > > > > >> consume as much as twice the memory than glibc > > > > > > >> > > > > > > >> 2. All existing Flink docker images use glibc, if we change > the > > > > > default > > > > > > >> memory allocator to jemalloc and only supply one series of > > images, > > > > we > > > > > > will > > > > > > >> leave those having better performance with glibc no other > > choices > > > > but > > > > > > >> staying with old images. In another word, there's a risk of > > > > > introducing > > > > > > new > > > > > > >> problems while fixing an existing one if choosing option-2. > > > > > > >> > > > > > > >> And there is a third option considering the efforts of > > maintaining > > > > > more > > > > > > >> images if the memory leak issue is not widely observed, that > we > > > > could > > > > > > >> document the steps of building Dockerfile with jemalloc as > > default > > > > > > >> allocator so users could build it when needed, which leaves > the > > > > burden > > > > > > to > > > > > > >> our users so for me it's not the best option. > > > > > > >> > > > > > > >> Best Regards, > > > > > > >> Yu > > > > > > >> > > > > > > >> [1] https://stackoverflow.com/a/33993215 > > > > > > >> > > > > > > >> On Tue, 13 Oct 2020 at 15:34, Yun Tang <myas...@live.com> > > wrote: > > > > > > >> > > > > > > >>> Hi all > > > > > > >>> > > > > > > >>> Users report they meet serious memory leak when submitting > jobs > > > > > > >>> continously in session mode within k8s (please refer to > > > > > FLINK-18712[1] > > > > > > ), > > > > > > >>> and I also reproduce this to find this is caused by memory > > > > > > fragmentation > > > > > > >> of > > > > > > >>> glibc [2][3] and provide solutions to fix this: > > > > > > >>> > > > > > > >>> * Quick but not very clean solution to limit the memory > > pool > > > > of > > > > > > >> glibc, > > > > > > >>> limit MALLOC_ARENA_MAX to 2 > > > > > > >>> > > > > > > >>> * More general solution by rebuilding the image to > install > > > > > > >>> libjemalloc-dev and add the libjemalloc.so it to LD_PRELOAD > > > > > > >>> > > > > > > >>> The reporter adopted the 2nd solution to fix this issue > > > eventually. > > > > > > Thus, > > > > > > >>> I begin to think whether we should change our Dockerfile to > > adopt > > > > > > >> jemalloc > > > > > > >>> as default memory allocator [4]. > > > > > > >>> From my point of view, we have two choices: > > > > > > >>> > > > > > > >>> 1. Introduce another Dockerfile using jemalloc as default > > > > memory > > > > > > >>> allocator, which means Flink needs another two new image tags > > to > > > > > build > > > > > > >>> docker with jemalloc while default docker still use glibc. > > > > > > >>> 2. Set the default memory allocator as jemalloc in our > > > existing > > > > > > >>> Dockerfiles, which means Flink offer docker image with > jemalloc > > > by > > > > > > >> default. > > > > > > >>> I prefer the 2nd option as our company already use jemalloc > as > > > > > default > > > > > > >>> memory allocator for JDK at our production environment due to > > > > > messages > > > > > > >> from > > > > > > >>> os team warning of glibc's memory fragmentation. > > > > > > >>> Moreover, I found several open source projects adopting > > jemalloc > > > as > > > > > > >>> default memory allocator within their images to resolve > memory > > > > > > >>> fragmentation problem, e.g fluent [5], home-assistant [6]. > > > > > > >>> > > > > > > >>> What do you guys think of this issue? > > > > > > >>> > > > > > > >>> [1] https://issues.apache.org/jira/browse/FLINK-18712 > > > > > > >>> [2] > > > > > > >>> > > > > > > >> > > > > > > > > > > > > > > > > > > > > > https://www.gnu.org/software/libc/manual/html_mono/libc.html#Freeing-after-Malloc > > > > > > >>> [3] https://sourceware.org/bugzilla/show_bug.cgi?id=15321 > > > > > > >>> [4] https://issues.apache.org/jira/browse/FLINK-19125 > > > > > > >>> [5] > > > > > > >>> > > > > > > >> > > > > > > > > > > > > > > > > > > > > > https://docs.fluentbit.io/manual/v/1.0/installation/docker#why-there-is-no-fluent-bit-docker-image-based-on-alpine-linux > > > > > > >>> [6] https://github.com/home-assistant/core/pull/33237 > > > > > > >>> > > > > > > >>> > > > > > > >>> Best > > > > > > >>> Yun Tang > > > > > > >>> > > > > > > > > > > > > > > > > > > > > > > > > > > >
