Re: anon_vma accumulating for certain load still not addressed

[Rik van Riel <riel@redhat.com>]

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 :)

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