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From: Paolo Bonzini <pbonzini@redhat.com>
To: Keqian Zhu <zhukeqian1@huawei.com>, Peter Xu <peterx@redhat.com>,
	qemu-devel@nongnu.org
Cc: Hyman <huangy81@chinatelecom.cn>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v5 09/10] KVM: Disable manual dirty log when dirty ring enabled
Date: Mon, 22 Mar 2021 14:55:44 +0100	[thread overview]
Message-ID: <47bfae75-9e2e-50da-a944-a45f64f41514@redhat.com> (raw)
In-Reply-To: <c49abf47-412c-26b8-0a28-c1007eed0159@huawei.com>

On 22/03/21 10:17, Keqian Zhu wrote:
> Hi Peter,
> 
> On 2021/3/11 4:33, Peter Xu wrote:
>> KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is for KVM_CLEAR_DIRTY_LOG, which is only
>> useful for KVM_GET_DIRTY_LOG.  Skip enabling it for kvm dirty ring.
>>
>> More importantly, KVM_DIRTY_LOG_INITIALLY_SET will not wr-protect all the pages
>> initially, which is against how kvm dirty ring is used - there's no way for kvm
>> dirty ring to re-protect a page before it's notified as being written first
>> with a GFN entry in the ring!  So when KVM_DIRTY_LOG_INITIALLY_SET is enabled
>> with dirty ring, we'll see silent data loss after migration.
> I feel a little regret that dirty ring can not work with KVM_DIRTY_LOG_INITIALLY_SET ...
> With KVM_DIRTY_LOG_INITIALLY_SET, we can speedup dirty log start. More important, we can
> enable dirty log gradually. For write fault based dirty log, it greatly reduces the side
> effect of dirty log over guest.
> 
> I hope we can put forward another similar optimization under dirty ring mode. :)

Indeed, perhaps (even though KVM_GET_DIRTY_LOG does not make sense with 
dirty ring) we could allow KVM_CLEAR_DIRTY_LOG.

Paolo



  reply	other threads:[~2021-03-22 14:11 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-10 20:32 [PATCH v5 00/10] KVM: Dirty ring support (QEMU part) Peter Xu
2021-03-10 20:32 ` [PATCH v5 01/10] memory: Introduce log_sync_global() to memory listener Peter Xu
2021-03-10 20:32 ` [PATCH v5 02/10] KVM: Use a big lock to replace per-kml slots_lock Peter Xu
2021-03-22 10:47   ` Keqian Zhu
2021-03-22 13:54     ` Paolo Bonzini
2021-03-22 16:27       ` Peter Xu
2021-03-24 18:08         ` Peter Xu
2021-03-10 20:32 ` [PATCH v5 03/10] KVM: Create the KVMSlot dirty bitmap on flag changes Peter Xu
2021-03-10 20:32 ` [PATCH v5 04/10] KVM: Provide helper to get kvm dirty log Peter Xu
2021-03-10 20:32 ` [PATCH v5 05/10] KVM: Provide helper to sync dirty bitmap from slot to ramblock Peter Xu
2021-03-10 20:32 ` [PATCH v5 06/10] KVM: Simplify dirty log sync in kvm_set_phys_mem Peter Xu
2021-03-10 20:32 ` [PATCH v5 07/10] KVM: Cache kvm slot dirty bitmap size Peter Xu
2021-03-10 20:32 ` [PATCH v5 08/10] KVM: Add dirty-gfn-count property Peter Xu
2021-03-10 20:33 ` [PATCH v5 09/10] KVM: Disable manual dirty log when dirty ring enabled Peter Xu
2021-03-22  9:17   ` Keqian Zhu
2021-03-22 13:55     ` Paolo Bonzini [this message]
2021-03-22 16:21       ` Peter Xu
2021-03-10 20:33 ` [PATCH v5 10/10] KVM: Dirty ring support Peter Xu
2021-03-22 13:37   ` Keqian Zhu
2021-03-22 18:52     ` Peter Xu
2021-03-23  1:25       ` Keqian Zhu
2021-03-19 18:12 ` [PATCH v5 00/10] KVM: Dirty ring support (QEMU part) Peter Xu
2021-03-22 14:02 ` Keqian Zhu
2021-03-22 19:45   ` Peter Xu
2021-03-23  6:40     ` Keqian Zhu
2021-03-23 14:34       ` Peter Xu
2021-03-24  2:56         ` Keqian Zhu
2021-03-24 15:09           ` Peter Xu
2021-03-25  1:21             ` Keqian Zhu

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