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.
Thanks,
--
Shannon
