On 05/12/2017 07:00, Yang Zhong wrote:
> On Mon, Dec 04, 2017 at 08:26:29PM +0800, Shannon Zhao wrote:
>> Hi Yang,
>>
>> On 2017/12/4 20:03, Yang Zhong wrote:
>>> On Fri, Dec 01, 2017 at 01:52:49PM +0100, Paolo Bonzini wrote:
>>>>> On 01/12/2017 11:56, Yang Zhong wrote:
>>>>>>> This issue should be caused by much times of system call by
>>>>>>> malloc_trim(),
>>>>>>> Shannon's test script include 60 scsi disks and 31 ioh3420 devices.
>>>>>>> We need
>>>>>>> trade-off between VM perforamance and memory optimization. Whether
>>>>>>> below
>>>>>>> method is suitable?
>>>>>>>
>>>>>>> int num=1;
>>>>>>> ......
>>>>>>>
>>>>>>> #if defined(CONFIG_MALLOC_TRIM)
>>>>>>> if(!(num++%5))
>>>>>>> {
>>>>>>> malloc_trim(4 * 1024 * 1024);
>>>>>>> }
>>>>>>> #endif
>>>>>>>
>>>>>>> Any comments are welcome! Thanks a lot!
>>>>>
>>>>> Indeed something like this will do, perhaps only trim once per second?
>>>>>
>>> Hello Paolo,
>>>
>>> Thanks for comments!
>>> If we do trim once per second, maybe the frequency is a little high,
>>> what'e
>>> more, we need maintain one timer to call this, this also cost cpu
>>> resource.
>>>
>>> I added the log and did the test here with my test qemu command, when VM
>>> bootup,
>>> which did more than 600 times free operations and 9 times memory trim in
>>> rcu
>>> thread. If i use our ClearContainer qemu command, the memory trim will
>>> down
>>> to 6 times. As for Shannon's test command, the malloc trim number will
>>> abosultly
>>> increse.
>>>
>>> In my above method, the trim is only executed in the multiple of 5, which
>>> will
>>> reduce trim times and do not heavily impact VM bootup performance.
>>>
>>> I also want to use synchronize_rcu() and free() to replace call_rcu(),
>>> but this
>>> method serialize to malloc() and free(), which will reduce VM performance.
>>>
>>> The ultimate aim is to reduce trim system call during the VM bootup and
>>> running.
>>> It's appreciated that if you have better suggestions.
>>
>> Maybe we can provide a QMP command or something else for user to trim
>> the heap manually like the kernel sysfs interface
>> /proc/sys/vm/drop_caches which provides an interface for user to drop
>> the caches.
>> So let user to decide whether it needs to trim the heap.
>>
> Hello Shannon,
>
> Thanks for your comments!
> This is also a good solution by QMP interface, but this is only suitable
> for few VMs.
> If there are millions of VMs in CSP(clouds of provider), it is very hard to
> operate.
> Thanks!
I agree, we only need to tweak the conditions under which malloc_trim is
called.
Thanks,
Paolo
