Re: [Qemu-devel] [PATCH] Permit zero-sized qemu_malloc() & friends

[malc]

On Sun, 6 Dec 2009, Avi Kivity wrote:

> On 12/06/2009 07:47 PM, malc wrote:
> > 
> > > It will never fail on Linux.  On other hosts it prevents a broken oom
> > > handler
> > > from taking the guest down a death spiral.
> > >      
> > It fails here all the time i'm sorry to say, i have overcommit disabled
> > (mostly because kpdf when doing a text search tends to overwhelm the VM
> > subsystem and Linux happily picks X11 as it's OOM kill target)
> >    
> 
> Right, I meant under the default configuration.  Unfortunately there is no
> good configuration for Linux - without strict overcommit you'll invoke the oom
> killer, with strict overcommit you'll need ridiculous amounts of swap because
> fork() and MAP_PRIVATE require tons of backing store.
> 
> On my home machine I have
> 
>   $ grep Commit /proc/meminfo
>   CommitLimit:     7235160 kB
>   Committed_AS:    4386172 kB
> 
> So, 4GB of virtual memory needed just to run a normal desktop with
> thunderbird+firefox.  Actual anonymous memory is less than 2GB, so you could
> easily run this workload on a 2GB machine without swap, but with strict
> overcommit 2GB RAM + 2GB swap will see failures even though you have free RAM.
> 

Well, i don't have a swap...

~$ cat /proc/meminfo 
MemTotal:       515708 kB
MemFree:          3932 kB
Buffers:         10120 kB
Cached:         365320 kB
SwapCached:          0 kB
Active:         238120 kB
Inactive:       222396 kB
SwapTotal:           0 kB
SwapFree:            0 kB
...
CommitLimit:    464136 kB
Committed_AS:   178920 kB
...

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