On 11/14/2014 08:08 AM, Michal Hocko wrote:
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?
I believe we should just merge that patch. I have not seen any better ideas come by. The comment should probably be fixed to reflect the chain length of 5 though :) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>