Re: ZONE_NORMAL memory exhausted by 4000 TCP sockets

[Eric Dumazet]

On Monday 06 November 2006 10:46, Zhao Xiaoming wrote:
> 2006/11/6, Eric Dumazet <dada1@xxxxxxxxxxxxx>:
> > On Monday 06 November 2006 09:59, Zhao Xiaoming wrote:
> > > Thank you again for your help. To have more detailed statistic data, I
> > > did another round of test and gathered some data.  I give the overall
> > > description here and detailed /proc/net/sockstat, /proc/meminfo,
> > > /proc/slabinfo and /proc/buddyinfo follows.
> > > =====================================================
> > >                            slab mem cost        tcp mem pages      
> > > lowmem free with traffic:             254668KB                 34693
> > >       38772KB
> > > without traffic:       104080KB                           1
> > >        702652KB
> > > =====================================================
> >
> > Thank you for detailed infos.
> >
> > It appears you have an extensive use of threads (about 10000), since :
> > > task_struct        10095  10095   1360    3    1 : tunables   24   12
> > >   8 : slabdata   3365   3365      0
> >
> > Each thread has a kernel stack, 8KB (ie 2 pages, order-1 allocation),
> > plus a user vma
> >
> > > vm_area_struct     21346  21504     92   42    1 : tunables  120   60
> > >   8 : slabdata    512    512      0
> >
> > Most likely you dont need that much threads. A program with fewer threads
> > will perform better and use less ram.
>
> Thanks for the comments. I known the threads may cost many memory.
> However, I already excluded them from the statistics. The 'after test'
> info was gotten while the 10000 threads running but no traffics
> relayed. You may look at the meminfo of 'after test', there is still
> 104080 kB slab memory which should already included the thread kernel
> memory cost (8K*10000=80MB). I know 10000 threads are not necessary
> and just use the simple logic to do some test.

In fact, your kernel has CONFIG_4KSTACKS, kernel thread stacks use 4K instead 
of 8K.

If you want to increase LOWMEM, (and keep 32bits kernel), you can chose a 
2G/2G user/kernel split, instead of the 3G/1G default split.
(see config : CONFIG_VMSPLIT_2G)

Eric
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