Re: [PATCH] kvm: fix slot flags sync between Qemu and KVM

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 04/08/2015 06:46 PM, Paolo Bonzini wrote:
>
>
> On 08/04/2015 08:34, Xiao Guangrong wrote:
>> We noticed that KVM keeps tracking dirty for the memslots when
>> live migration failed which causes bad performance due to huge
>> page mapping disallowed for this kind of memslot
>>
>> It is caused by slot flags does not properly sync-ed between Qemu
>> and KVM. Current code doing slot update depends on slot->flags
>> which hopes to omit unnecessary ioctl. However, slot->flags only
>> reflects the stauts of corresponding memory region, vmsave and
>> live migration do dirty tracking which overset
>> KVM_MEM_LOG_DIRTY_PAGES for the slot. That causes the slot status
>> recorded in the flags does not exactly match the stauts in kernel.
>>
>> We fixed it by introducing slot->is_dirty_logging which indicates
>> the dirty status in kernel so that it helps us to sync the status
>> between userspace and kernel
>>
>> Wanpeng Li <wanpeng.li@linux.intel.com>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>
> Hi Xiao,
>
> the patch looks good.
>
> However, I am planning to remove s->migration_log completely from QEMU
> 2.4 and have slot->flags also track the migration state.  This has the
> side effect of fixing this bug.  I'll Cc you on the patches when I post
> them (next week probably).

Good to know it, look forward to your patches. Thank you, Paolo!