On Mon, Mar 2, 2020, 5:38 AM Zhoujian (jay) <jianjay.z...@huawei.com> wrote:
> > > > -----Original Message----- > > From: Peter Feiner [mailto:pfei...@google.com] > > Sent: Saturday, February 22, 2020 8:19 AM > > To: Junaid Shahid <juna...@google.com> > > Cc: Ben Gardon <bgar...@google.com>; Zhoujian (jay) > > <jianjay.z...@huawei.com>; Peter Xu <pet...@redhat.com>; > > k...@vger.kernel.org; qemu-devel@nongnu.org; pbonz...@redhat.com; > > dgilb...@redhat.com; quint...@redhat.com; Liujinsong (Paul) > > <liu.jins...@huawei.com>; linfeng (M) <linfen...@huawei.com>; wangxin > (U) > > <wangxinxin.w...@huawei.com>; Huangweidong (C) > > <weidong.hu...@huawei.com> > > Subject: Re: RFC: Split EPT huge pages in advance of dirty logging > > > > On Fri, Feb 21, 2020 at 2:08 PM Junaid Shahid <juna...@google.com> > wrote: > > > > > > On 2/20/20 9:34 AM, Ben Gardon wrote: > > > > > > > > FWIW, we currently do this eager splitting at Google for live > > > > migration. When the log-dirty-memory flag is set on a memslot we > > > > eagerly split all pages in the slot down to 4k granularity. > > > > As Jay said, this does not cause crippling lock contention because > > > > the vCPU page faults generated by write protection / splitting can > > > > be resolved in the fast page fault path without acquiring the MMU > lock. > > > > I believe +Junaid Shahid tried to upstream this approach at some > > > > point in the past, but the patch set didn't make it in. (This was > > > > before my time, so I'm hoping he has a link.) I haven't done the > > > > analysis to know if eager splitting is more or less efficient with > > > > parallel slow-path page faults, but it's definitely faster under the > > > > MMU lock. > > > > > > > > > > I am not sure if we ever posted those patches upstream. Peter Feiner > would > > know for sure. One notable difference in what we do compared to the > approach > > outlined by Jay is that we don't rely on tdp_page_fault() to do the > splitting. So we > > don't have to create a dummy VCPU and the specialized split function is > also > > much faster. > > > > We've been carrying these patches since 2015. I've never posted them. > > Getting them in shape for upstream consumption will take some work. I > can look > > into this next week. > > Hi Peter Feiner, > > May I ask any new updates about your plan? Sorry to disturb. > Hi Jay, I've been sick since I sent my last email, so I haven't gotten to this patch set yet. I'll send it in the next week or two. Peter > Regards, > Jay Zhou >
