Re: [PATCH v33 0/4] Virtio-balloon: support free page reporting
On Fri, 15 Jun 2018 12:43:09 +0800 Wei Wang wrote: > This patch series is separated from the previous "Virtio-balloon > Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT, > implemented by this series enables the virtio-balloon driver to report > hints of guest free pages to the host. It can be used to accelerate live > migration of VMs. Here is an introduction of this usage: So, we have two page hinting solutions being proposed. One is this series, the other one by Nitesh is intended to improve host memory utilization by letting the host use unused guest memory[1]. Instead of merging two similar solutions, do we want a more generic one that solves both problems? Or maybe an unified solution? [1] https://www.spinics.net/lists/kvm/msg170113.html > Live migration needs to transfer the VM's memory from the source machine > to the destination round by round. For the 1st round, all the VM's memory > is transferred. From the 2nd round, only the pieces of memory that were > written by the guest (after the 1st round) are transferred. One method > that is popularly used by the hypervisor to track which part of memory is > written is to write-protect all the guest memory. > > This feature enables the optimization by skipping the transfer of guest > free pages during VM live migration. It is not concerned that the memory > pages are used after they are given to the hypervisor as a hint of the > free pages, because they will be tracked by the hypervisor and transferred > in the subsequent round if they are used and written. > > * Tests > - Test Environment > Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz > Guest: 8G RAM, 4 vCPU > Migration setup: migrate_set_speed 100G, migrate_set_downtime 2 second > > - Test Results > - Idle Guest Live Migration Time (results are averaged over 10 runs): > - Optimization v.s. Legacy = 278ms vs 1757ms --> ~84% reduction > - Guest with Linux Compilation Workload (make bzImage -j4): > - Live Migration Time (average) > Optimization v.s. Legacy = 1408ms v.s. 2528ms --> ~44% reduction > - Linux Compilation Time > Optimization v.s. Legacy = 5min3s v.s. 5min12s > --> no obvious difference > > ChangeLog: > v32->v33: > - mm/get_from_free_page_list: The new implementation to get free page > hints based on the suggestions from Linus: > https://lkml.org/lkml/2018/6/11/764 > This avoids the complex call chain, and looks more prudent. > - virtio-balloon: > - use a fix-sized buffer to get free page hints; > - remove the cmd id related interface. Now host can just send a free > page hint command to the guest (via the host_cmd config register) > to start the reporting. Currentlty the guest reports only the max > order free page hints to host, which has generated similar good > results as before. But the interface used by virtio-balloon to > report can support reporting more orders in the future when there > is a need. > v31->v32: > - virtio-balloon: > - rename cmd_id_use to cmd_id_active; > - report_free_page_func: detach used buffers after host sends a vq > interrupt, instead of busy waiting for used buffers. > v30->v31: > - virtio-balloon: > - virtio_balloon_send_free_pages: return -EINTR rather than 1 to > indicate an active stop requested by host; and add more > comments to explain about access to cmd_id_received without > locks; > - add_one_sg: add TODO to comments about possible improvement. > v29->v30: > - mm/walk_free_mem_block: add cond_sched() for each order > v28->v29: > - mm/page_poison: only expose page_poison_enabled(), rather than more > changes did in v28, as we are not 100% confident about that for now. > - virtio-balloon: use a separate buffer for the stop cmd, instead of > having the start and stop cmd use the same buffer. This avoids the > corner case that the start cmd is overridden by the stop cmd when > the host has a delay in reading the start cmd. > v27->v28: > - mm/page_poison: Move PAGE_POISON to page_poison.c and add a function > to expose page poison val to kernel modules. > v26->v27: > - add a new patch to expose page_poisoning_enabled to kernel modules > - virtio-balloon: set poison_val to 0x, instead of 0xaa > v25->v26: virtio-balloon changes only > - remove kicking free page vq since the host now polls the vq after > initiating the reporting > - report_free_page_func: detach all the used buffers after sending > the stop cmd id. This avoids leaving the detaching burden (i.e. > overhead) to the next cmd id. Detaching here isn't considered > overhead since the stop cmd id has been sent, and host has already > moved formard. > v24->v25: > - mm: change walk_free_mem_block to return 0 (instead of
Re: [PATCH v33 0/4] Virtio-balloon: support free page reporting
On Fri, Jun 15, 2018 at 02:28:49PM +, Wang, Wei W wrote: > On Friday, June 15, 2018 7:30 PM, Michael S. Tsirkin wrote: > > On Fri, Jun 15, 2018 at 12:43:09PM +0800, Wei Wang wrote: > > > - remove the cmd id related interface. Now host can just send a free > > > page hint command to the guest (via the host_cmd config register) > > > to start the reporting. > > > > Here we go again. And what if reporting was already started previously? > > I don't think it's a good idea to tweak the host/guest interface yet again. > > This interface is much simpler, and I'm not sure if that would be an > issue here now, because now the guest delivers the whole buffer of > hints to host once, instead of hint by hint as before. And the guest > notifies host after the buffer is delivered. In any case, the host > doorbell handler will be invoked, if host doesn't need the hints at > that time, it will just give back the buffer. There will be no stale > hints remained in the ring now. > > Best, > Wei I still think all the old arguments for cmd id apply. -- MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PATCH v33 0/4] Virtio-balloon: support free page reporting
On Fri, Jun 15, 2018 at 12:43:09PM +0800, Wei Wang wrote: > - remove the cmd id related interface. Now host can just send a free > page hint command to the guest (via the host_cmd config register) > to start the reporting. Here we go again. And what if reporting was already started previously? I don't think it's a good idea to tweak the host/guest interface yet again. -- MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
[PATCH v33 0/4] Virtio-balloon: support free page reporting
This patch series is separated from the previous "Virtio-balloon Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT, implemented by this series enables the virtio-balloon driver to report hints of guest free pages to the host. It can be used to accelerate live migration of VMs. Here is an introduction of this usage: Live migration needs to transfer the VM's memory from the source machine to the destination round by round. For the 1st round, all the VM's memory is transferred. From the 2nd round, only the pieces of memory that were written by the guest (after the 1st round) are transferred. One method that is popularly used by the hypervisor to track which part of memory is written is to write-protect all the guest memory. This feature enables the optimization by skipping the transfer of guest free pages during VM live migration. It is not concerned that the memory pages are used after they are given to the hypervisor as a hint of the free pages, because they will be tracked by the hypervisor and transferred in the subsequent round if they are used and written. * Tests - Test Environment Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz Guest: 8G RAM, 4 vCPU Migration setup: migrate_set_speed 100G, migrate_set_downtime 2 second - Test Results - Idle Guest Live Migration Time (results are averaged over 10 runs): - Optimization v.s. Legacy = 278ms vs 1757ms --> ~84% reduction - Guest with Linux Compilation Workload (make bzImage -j4): - Live Migration Time (average) Optimization v.s. Legacy = 1408ms v.s. 2528ms --> ~44% reduction - Linux Compilation Time Optimization v.s. Legacy = 5min3s v.s. 5min12s --> no obvious difference ChangeLog: v32->v33: - mm/get_from_free_page_list: The new implementation to get free page hints based on the suggestions from Linus: https://lkml.org/lkml/2018/6/11/764 This avoids the complex call chain, and looks more prudent. - virtio-balloon: - use a fix-sized buffer to get free page hints; - remove the cmd id related interface. Now host can just send a free page hint command to the guest (via the host_cmd config register) to start the reporting. Currentlty the guest reports only the max order free page hints to host, which has generated similar good results as before. But the interface used by virtio-balloon to report can support reporting more orders in the future when there is a need. v31->v32: - virtio-balloon: - rename cmd_id_use to cmd_id_active; - report_free_page_func: detach used buffers after host sends a vq interrupt, instead of busy waiting for used buffers. v30->v31: - virtio-balloon: - virtio_balloon_send_free_pages: return -EINTR rather than 1 to indicate an active stop requested by host; and add more comments to explain about access to cmd_id_received without locks; - add_one_sg: add TODO to comments about possible improvement. v29->v30: - mm/walk_free_mem_block: add cond_sched() for each order v28->v29: - mm/page_poison: only expose page_poison_enabled(), rather than more changes did in v28, as we are not 100% confident about that for now. - virtio-balloon: use a separate buffer for the stop cmd, instead of having the start and stop cmd use the same buffer. This avoids the corner case that the start cmd is overridden by the stop cmd when the host has a delay in reading the start cmd. v27->v28: - mm/page_poison: Move PAGE_POISON to page_poison.c and add a function to expose page poison val to kernel modules. v26->v27: - add a new patch to expose page_poisoning_enabled to kernel modules - virtio-balloon: set poison_val to 0x, instead of 0xaa v25->v26: virtio-balloon changes only - remove kicking free page vq since the host now polls the vq after initiating the reporting - report_free_page_func: detach all the used buffers after sending the stop cmd id. This avoids leaving the detaching burden (i.e. overhead) to the next cmd id. Detaching here isn't considered overhead since the stop cmd id has been sent, and host has already moved formard. v24->v25: - mm: change walk_free_mem_block to return 0 (instead of true) on completing the report, and return a non-zero value from the callabck, which stops the reporting. - virtio-balloon: - use enum instead of define for VIRTIO_BALLOON_VQ_INFLATE etc. - avoid __virtio_clear_bit when bailing out; - a new method to avoid reporting the some cmd id to host twice - destroy_workqueue can cancel free page work when the feature is negotiated; - fail probe when the free page vq size is less than 2. v23->v24: - change feature name VIRTIO_BALLOON_F_FREE_PAGE_VQ to
