On 3/6/19 11:09 AM, Michael S. Tsirkin wrote: > On Wed, Mar 06, 2019 at 10:50:42AM -0500, Nitesh Narayan Lal wrote: >> The following patch-set proposes an efficient mechanism for handing freed >> memory between the guest and the host. It enables the guests with no page >> cache to rapidly free and reclaims memory to and from the host respectively. >> >> Benefit: >> With this patch-series, in our test-case, executed on a single system and >> single NUMA node with 15GB memory, we were able to successfully launch 5 >> guests(each with 5 GB memory) when page hinting was enabled and 3 without >> it. (Detailed explanation of the test procedure is provided at the bottom >> under Test - 1). >> >> Changelog in v9: >> * Guest free page hinting hook is now invoked after a page has been >> merged in the buddy. >> * Free pages only with order FREE_PAGE_HINTING_MIN_ORDER(currently >> defined as MAX_ORDER - 1) are captured. >> * Removed kthread which was earlier used to perform the scanning, >> isolation & reporting of free pages. >> * Pages, captured in the per cpu array are sorted based on the zone >> numbers. This is to avoid redundancy of acquiring zone locks. >> * Dynamically allocated space is used to hold the isolated guest >> free pages. >> * All the pages are reported asynchronously to the host via virtio >> driver. >> * Pages are returned back to the guest buddy free list only when the >> host response is received. >> >> Pending items: >> * Make sure that the guest free page hinting's current >> implementation doesn't break hugepages or device assigned guests. >> * Follow up on VIRTIO_BALLOON_F_PAGE_POISON's device side support. (It >> is currently missing) >> * Compare reporting free pages via vring with vhost. >> * Decide between MADV_DONTNEED and MADV_FREE. >> * Analyze overall performance impact due to guest free page hinting. >> * Come up with proper/traceable error-message/logs. >> >> Tests: >> 1. Use-case - Number of guests we can launch >> >> NUMA Nodes = 1 with 15 GB memory >> Guest Memory = 5 GB >> Number of cores in guest = 1 >> Workload = test allocation program allocates 4GB memory, touches it via >> memset and exits. >> Procedure = >> The first guest is launched and once its console is up, the test >> allocation program is executed with 4 GB memory request (Due to this the >> guest occupies almost 4-5 GB of memory in the host in a system without page >> hinting). Once this program exits at that time another guest is launched in >> the host and the same process is followed. We continue launching the guests >> until a guest gets killed due to low memory condition in the host. >> >> Results: >> Without hinting = 3 >> With hinting = 5 >> >> 2. Hackbench >> Guest Memory = 5 GB >> Number of cores = 4 >> Number of tasks Time with Hinting Time without Hinting >> 4000 19.540 17.818 >> > How about memhog btw? > Alex reported: > > My testing up till now has consisted of setting up 4 8GB VMs on a system > with 32GB of memory and 4GB of swap. To stress the memory on the system > I > would run "memhog 8G" sequentially on each of the guests and observe how > long it took to complete the run. The observed behavior is that on the > systems with these patches applied in both the guest and on the host I > was > able to complete the test with a time of 5 to 7 seconds per guest. On a > system without these patches the time ranged from 7 to 49 seconds per > guest. I am assuming the variability is due to time being spent writing > pages out to disk in order to free up space for the guest. > Here are the results:
Procedure: 3 Guests of size 5GB is launched on a single NUMA node with total memory of 15GB and no swap. In each of the guest, memhog is run with 5GB. Post-execution of memhog, Host memory usage is monitored by using Free command. Without Hinting: Time of execution Host used memory Guest 1: 45 seconds 5.4 GB Guest 2: 45 seconds 10 GB Guest 3: 1 minute 15 GB With Hinting: Time of execution Host used memory Guest 1: 49 seconds 2.4 GB Guest 2: 40 seconds 4.3 GB Guest 3: 50 seconds 6.3 GB -- Regards Nitesh
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