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Re: [Qemu-devel] qemu core file size

From: Wanpeng Li
Subject: Re: [Qemu-devel] qemu core file size
Date: Tue, 7 Nov 2017 14:02:41 +0800

Hi Alexey,
2017-11-07 13:46 GMT+08:00 Alexey Kardashevskiy <address@hidden>:
> On 07/11/17 01:08, Paolo Bonzini wrote:
>> On 06/11/2017 13:18, Wanpeng Li wrote:
>>> 2017-11-06 20:02 GMT+08:00 Paolo Bonzini <address@hidden>:
>>>> On 06/11/2017 12:59, Fam Zheng wrote:
>>>>>>> Could you point out the patchset for the fix?
>>>>>> Between 447b0d0b9ee8a0ac216c3186e0f3c427a1001f0c and
>>>>>> 092aa2fc65b7a35121616aad8f39d47b8f921618.
>>>>> Not sure how these relate to the core size, but I've tested upstream
>>>>> (ec7a8bf0b8f7dc7288fe8745464ee8217528cc6c) and with dump-guest-core=off 
>>>>> the core
>>>>> file is 363M, still significantly larger than rss (~73M).
>>>>> What is bloating the core file?
>>>> My guess would have been fragmented heap.  The core file, unlike the
>>>> RSS, includes all the mmaped memory (e.g. from shared libraries) that
>>>> has never been used.
>>>> For example, all the Ceph/Gluster/PulseAudio/SPICE/whatever libraries
>>>> are included in the core file but likely are not in the RSS.
>>> Do you mean not use Memory API will avoid the fragmented heap?
>> The high memory usage from the memory API causes excessive
>> fragmentation.  Alexey's work should help reducing memory usage and thus
>> the fragmentation.
> Since centos6 does not have this issue and centos7 does, I'd suggest
> https://www.gnu.org/software/libc/manual/html_node/Memory-Allocation-Tunables.html

Thanks for the inputs. What's the recommend glibc.malloc.arena_max
value from you? :)

> glibc changed some defaults between rhel/centos 6 and 7 if I recall
> correctly, and these arenas now create big anon mappings per thread, these
> are not really touched (so they do not use resident memory) but may appear
> in these dumps, dunno.
> btw do you configure the machine to make "kill -11" produce qemu core dumps?

Yeah, some tuning in /etc/libvirt/qemu.conf, max_core="unlimited",

Wanpeng Li

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