Messages in this thread | | | Date | Fri, 14 Nov 2014 14:08:22 +0100 | From | Michal Hocko <> | Subject | anon_vma accumulating for certain load still not addressed |
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Hi, back in 2012 [1] there was a discussion about a forking load which accumulates anon_vmas. There was a trivial test case which triggers this and can potentially deplete the memory by local user.
We have a report for an older enterprise distribution where nsd is suffering from this issue most probably (I haven't debugged it throughly but accumulating anon_vma structs over time sounds like a good enough fit) and has to be restarted after some time to release the accumulated anon_vma objects.
There was a patch which tried to work around the issue [2] but I do not see any follow ups nor any indication that the issue would be addressed in other way.
The test program from [1] was running for around 39 mins on my laptop and here is the result:
$ date +%s; grep anon_vma /proc/slabinfo 1415960225 anon_vma 11664 11900 160 25 1 : tunables 0 0 0 : slabdata 476 476 0
$ ./a # The reproducer
$ date +%s; grep anon_vma /proc/slabinfo 1415962592 anon_vma 34875 34875 160 25 1 : tunables 0 0 0 : slabdata 1395 1395 0
$ killall a $ date +%s; grep anon_vma /proc/slabinfo 1415962607 anon_vma 11277 12175 160 25 1 : tunables 0 0 0 : slabdata 487 487 0
So we have accumulated 23211 objects over that time period before the offender was killed which released all of them.
The proposed workaround is kind of ugly but do people have a better idea than reference counting? If not should we merge it?
--- [1] https://lkml.org/lkml/2012/8/15/765 [2] https://lkml.org/lkml/2013/6/3/568 -- Michal Hocko SUSE Labs
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