Re: [PATCH 0/1] KVM: make get dirty log ioctl return the first dirty page's position

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Avi Kivity wrote:

Seems to confirm - not much can be skipped.



>> kvm_get_map(slot 1): r= 2044, slot.len= 535822336(2044)
Am I wrong? in this case, the return value is suggesting
we can skip every 2044(the value in the bracket) bitmap check, right?

Er, I was wrong, I thought the value in the brackets had the same units as slots.len. But it's in units of ulongs.

In this case, the entire bitmap can be skipped, so the saving would be significant. But this is for an idle load, where we'll converge quickly anyway. For a busy server, things will look different.

So I recommend you look at the double buffer approach. This can eliminate the kernel scan, the copying, and the userspace scan entirely, as well as remove the vmalloc().


OK, I want to try! Thanks for advice.

 Takuya
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