On Tue, May 5, 2020 at 4:54 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote:
>
> CC-ing stable@xxxxxxxxxxxxxxx and adding some more explanations.
>
> On Tue, 5 May 2020 10:10:33 +0200 SeongJae Park <sjpark@xxxxxxxxxx> wrote:
>
> > From: SeongJae Park <sjpark@xxxxxxxxx>
> >
> > The commit 6d7855c54e1e ("sockfs: switch to ->free_inode()") made the
> > deallocation of 'socket_alloc' to be done asynchronously using RCU, as
> > same to 'sock.wq'. And the following commit 333f7909a857 ("coallocate
> > socket_sq with socket itself") made those to have same life cycle.
> >
> > The changes made the code much more simple, but also made 'socket_alloc'
> > live longer than before. For the reason, user programs intensively
> > repeating allocations and deallocations of sockets could cause memory
> > pressure on recent kernels.
>
> I found this problem on a production virtual machine utilizing 4GB memory while
> running lebench[1]. The 'poll big' test of lebench opens 1000 sockets, polls
> and closes those. This test is repeated 10,000 times. Therefore it should
> consume only 1000 'socket_alloc' objects at once. As size of socket_alloc is
> about 800 Bytes, it's only 800 KiB. However, on the recent kernels, it could
> consume up to 10,000,000 objects (about 8 GiB). On the test machine, I
> confirmed it consuming about 4GB of the system memory and results in OOM.
>
> [1] https://github.com/LinuxPerfStudy/LEBench
To be fair, I have not backported Al patches to Google production
kernels, nor I have tried this benchmark.
Why do we have 10,000,000 objects around ? Could this be because of
some RCU problem ?
Once Al patches reverted, do you have 10,000,000 sock_alloc around ?
Thanks.
>
> >
> > To avoid the problem, this commit reverts the changes.
>
> I also tried to make fixup rather than reverts, but I couldn't easily find
> simple fixup. As the commits 6d7855c54e1e and 333f7909a857 were for code
> refactoring rather than performance optimization, I thought introducing complex
> fixup for this problem would make no sense. Meanwhile, the memory pressure
> regression could affect real machines. To this end, I decided to quickly
> revert the commits first and consider better refactoring later.
>
>
> Thanks,
> SeongJae Park
>
> >
> > SeongJae Park (2):
> > Revert "coallocate socket_wq with socket itself"
> > Revert "sockfs: switch to ->free_inode()"
> >
> > drivers/net/tap.c | 5 +++--
> > drivers/net/tun.c | 8 +++++---
> > include/linux/if_tap.h | 1 +
> > include/linux/net.h | 4 ++--
> > include/net/sock.h | 4 ++--
> > net/core/sock.c | 2 +-
> > net/socket.c | 23 ++++++++++++++++-------
> > 7 files changed, 30 insertions(+), 17 deletions(-)
> >
> > --
> > 2.17.1
