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([2001:8003:e5b0:9f00:dbbc:1945:6e65:ec5]) by smtp.gmail.com with ESMTPSA id w20-20020a639354000000b00564be149a15sm205429pgm.65.2023.08.30.17.55.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Aug 2023 17:55:34 -0700 (PDT) Message-ID: Date: Thu, 31 Aug 2023 10:55:29 +1000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] virtio_balloon: Fix endless deflation and inflation on arm64 Content-Language: en-US To: David Hildenbrand , virtualization@lists.linux-foundation.org Cc: linux-kernel@vger.kernel.org, jasowang@redhat.com, mst@redhat.com, xuanzhuo@linux.alibaba.com, shan.gavin@gmail.com References: <20230829015421.920511-1-gshan@redhat.com> From: Gavin Shan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/31/23 02:30, David Hildenbrand wrote: > On 29.08.23 03:54, Gavin Shan wrote: >> The deflation request to the target, which isn't unaligned to the >> guest page size causes endless deflation and inflation actions. For >> example, we receive the flooding QMP events for the changes on memory >> balloon's size after a deflation request to the unaligned target is >> sent for the ARM64 guest, where we have 64KB base page size. >> >>    /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64      \ >>    -accel kvm -machine virt,gic-version=host -cpu host          \ >>    -smp maxcpus=8,cpus=8,sockets=2,clusters=2,cores=2,threads=1 \ >>    -m 1024M,slots=16,maxmem=64G                                 \ >>    -object memory-backend-ram,id=mem0,size=512M                 \ >>    -object memory-backend-ram,id=mem1,size=512M                 \ >>    -numa node,nodeid=0,memdev=mem0,cpus=0-3                     \ >>    -numa node,nodeid=1,memdev=mem1,cpus=4-7                     \ >>      :                                                          \ >>    -device virtio-balloon-pci,id=balloon0,bus=pcie.10 >> >>    { "execute" : "balloon", "arguments": { "value" : 1073672192 } } >>    {"return": {}} >>    {"timestamp": {"seconds": 1693272173, "microseconds": 88667},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272174, "microseconds": 89704},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272175, "microseconds": 90819},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272176, "microseconds": 91961},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272177, "microseconds": 93040},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}} >>    {"timestamp": {"seconds": 1693272178, "microseconds": 94117},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}} >>    {"timestamp": {"seconds": 1693272179, "microseconds": 95337},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272180, "microseconds": 96615},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}} >>    {"timestamp": {"seconds": 1693272181, "microseconds": 97626},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272182, "microseconds": 98693},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}} >>    {"timestamp": {"seconds": 1693272183, "microseconds": 99698},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272184, "microseconds": 100727},  \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272185, "microseconds": 90430},   \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    {"timestamp": {"seconds": 1693272186, "microseconds": 102999},  \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073676288}} >>       : >>    >> >> Fix it by having the target aligned to the guest page size, 64KB >> in this specific case. With this applied, no flooding QMP event >> is observed and the memory balloon's size can be stablizied to >> 0x3ffe0000 soon after the deflation request is sent. >> >>    { "execute" : "balloon", "arguments": { "value" : 1073672192 } } >>    {"return": {}} >>    {"timestamp": {"seconds": 1693273328, "microseconds": 793075},  \ >>     "event": "BALLOON_CHANGE", "data": {"actual": 1073610752}} >>    { "execute" : "query-balloon" } >>    {"return": {"actual": 1073610752}} >> >> Signed-off-by: Gavin Shan >> --- >>   drivers/virtio/virtio_balloon.c | 13 ++++++++++++- >>   1 file changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index 5b15936a5214..625caac35264 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -386,6 +386,17 @@ static void stats_handle_request(struct virtio_balloon *vb) >>       virtqueue_kick(vq); >>   } >> +static inline s64 align_pages_up(s64 diff) >> +{ >> +    if (diff == 0) >> +        return diff; >> + >> +    if (diff > 0) >> +        return ALIGN(diff, VIRTIO_BALLOON_PAGES_PER_PAGE); >> + >> +    return -ALIGN(-diff, VIRTIO_BALLOON_PAGES_PER_PAGE); >> +} >> + >>   static inline s64 towards_target(struct virtio_balloon *vb) >>   { >>       s64 target; >> @@ -396,7 +407,7 @@ static inline s64 towards_target(struct virtio_balloon *vb) >>               &num_pages); >>       target = num_pages; >> -    return target - vb->num_pages; > > We know that vb->num_pages is always multiples of VIRTIO_BALLOON_PAGES_PER_PAGE. > > Why not simply align target down? > > target = ALIGN(num_pages, VIRTIO_BALLOON_PAGES_PER_PAGE); > return target - vb->num_pages; > Good point. Thanks a lot, David. The code will be changed to what's suggested in v2, to be posted soon. I will also add a comment to explain it a bit. Besides, ALIGN() is align-up instead of align-down to give bias to deflation intentionally, to avoid overrunning the machine's memory size if it's not aligned to 64KB. Further more, the align-up causes deflation even user requests a 4KB diff. However, the outcome of ALIGN_DOWN(4KB, 64KB) is zero and no deflation will be triggered. Thanks, Gavin