On 06/12/2017 10:26, Yang Zhong wrote:
> Hello Paolo,
>
> The best option is only trim one time after guest kernel bootup or VM
> bootup, and as for
> hotplug/unhotplug operations during the VM running, the trim still can do
> for each batch
> memory free because trim will not impact VM performance during VM running
> status.
>
> So, the key point is qemu is hard to know when guest ernel bootup is over.
> If you have some
> suggestions, please let me know. thanks!
It shouldn't be hard. Does QEMU's RCU thread actually get any
significant activity after bootup? Hence the suggestion of keeping
malloc_trim in the RCU thread, but only do it if some time has passed
since the last time.
Maybe something like this every time the RCU thread runs:
static uint64_t next_trim_time, last_trim_time;
if (current time < next_trim_time) {
next_trim_time -= last_trim_time / 2 /* or higher */
last_trim_time -= last_trim_time / 2 /* same as previous line */
} else {
trim_start_time = current time
malloc_trim(...)
last_trim_time = current time - trim_start_time
next_trim_time = current time + last_trim_time
}
Where the "2" factor should be tuned so that both your and Shannon's
scenario work fine.
Thanks,
Paolo
