On 7/11/19 10:58 AM, Alexander Duyck wrote: > On Thu, Jul 11, 2019 at 4:31 AM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote: >> >> On 7/10/19 7:40 PM, Alexander Duyck wrote: >>> On Wed, Jul 10, 2019 at 12:52 PM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote: >>> >>> The results up here were redundant with what is below so I am just >>> dropping them. I would suggest only including one set of results in >>> any future cover page as it is confusing to duplicate it like that. >>> >>>> This approach tracks all freed pages of the order MAX_ORDER - 2 in bitmaps. >>>> A new hook after buddy merging is used to set the bits in the bitmap. >>>> Currently, the bits are only cleared when pages are hinted, not when pages are >>>> re-allocated. >>>> >>>> Bitmaps are stored on a per-zone basis and are protected by the zone lock. A >>>> workqueue asynchronously processes the bitmaps as soon as a pre-defined memory >>>> threshold is met, trying to isolate and report pages that are still free. >>>> >>>> The isolated pages are reported via virtio-balloon, which is responsible for >>>> sending batched pages to the host synchronously. Once the hypervisor processed >>>> the hinting request, the isolated pages are returned back to the buddy. >>>> >>>> Changelog in v11: >>>> * Added logic to take care of multiple NUMA nodes scenarios. >>>> * Simplified the logic for reporting isolated pages to the host. (Eg. replaced >>>> dynamically allocated arrays with static ones, introduced wait event instead of >>>> the loop in order to wait for a response from the host) >>>> * Added a mutex to prevent race condition when page hinting is enabled by >>>> multiple drivers. >>>> * Simplified the logic responsible for decrementing free page counter for each >>>> zone. >>>> * Simplified code structuring/naming. >>>> >>>> Known work items for the future: >>>> * Test device assigned guests to ensure that hinting doesn't break it. >>>> * Follow up on VIRTIO_BALLOON_F_PAGE_POISON's device-side support. >>>> * Decide between MADV_DONTNEED and MADV_FREE. >>>> * Look into memory hotplug, more efficient locking, better naming conventions to >>>> avoid confusion with VIRTIO_BALLOON_F_FREE_PAGE_HINT support. >>>> * Come up with proper/traceable error-message/logs and look into other code >>>> simplifications. (If necessary). >>>> >>>> Benefit analysis: >>>> 1. Number of 5GB guests (each touching 4GB memory) that can be launched without >>>> swap usage on a system with 15GB: >>>> unmodified kernel - 2, 3rd with 2.5GB >>>> v11 page hinting - 6, 7th with 26MB >>>> v1 bubble hinting - 6, 7th with 1.8GB >>>> >>>> Conclusion - In this particular testcase on using v11 page hinting and >>>> v1 bubble-hinting 4 more guests could be launched without swapping compared >>>> to an unmodified kernel. >>>> For the 7th guest launch, v11 page hinting is slightly better than v1 Bubble >>>> hinting as it touches lesser swap space. >>> I'm confused by the comment. From what I can tell bubble hinting came >>> up with 1.8GB of memory while page hinting only managed to achieve >>> .026GB (Using the same units makes it easier to visualize the >>> difference). Also your test says "can be launched without swap usage", >>> yet you say the bubble hinting is touching swap which makes not sense >>> to me. >> I will work on the cover to improve this part. >> Basically, In each case, the first number indicates the number of the >> guest which are launched without touching the swap space. For instance >> with bubble hinting, I was able to launch 6 guests without any swap >> usage. On launching the 7th guests initially there was no swap usage, >> however, as the test app starts allocating 4GB memory the swap came into >> the picture. 1.8 GB is the swap usage after the completion of the test >> application. >>>> Setup & procedure - >>>> Total NUMA Node Memory ~ 15 GB (All guests are run on a single NUMA node) >>>> Guest Memory = 5GB >>>> Number of CPUs in the guest = 1 >>>> Host swap = 4GB >>>> Workload = test allocation program that allocates 4GB memory, touches it via >>>> memset and exits. >>>> 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. It is continued until the swap is not used. >>>> >>>> 2. Memhog execution time (For 3 guests each of 6GB on a system with 15GB): >>>> unmodified kernel - Guest1:21s, Guest2:27s, Guest3:2m37s swap used = 3.7GB >>>> v11 page hinting - Guest1:23s, Guest2:26s, Guest3:21s swap used = 0 >>>> v1 bubble hinting - Guest1:23, Guest2:11s, Guest3:26s swap used = 0 >>>> >>>> For this particular test-case in a guest which doesn't require swap access >>>> "memhog 6G" execution time lies within a range of 15-30s. >>>> Conclusion - >>>> In the above test case for an unmodified kernel on executing memhog in the >>>> third guest execution time rises to above 2minutes due to swap access. >>>> Using either page-hinting or bubble hinting brings this execution time to a >>>> a normal range of 15-30s. >>> So really this test doesn't add much in value. The whole reason why >>> Guest3 runs so much slower is because it is going to swap. I initially >>> did this to demonstrate a point, but now running this test doesn't >>> prove much as it isn't really meant to be a performance test. It is >>> essentially just a duplicate of the "how many guests can you run" test >>> that is passing itself off as some sort of performance test. >>> >>> We could probably just drop this from future version of this as long >>> as we verify that the memory hinting is freeing most of the memory >>> back and the guest is reporting a size less than the total guest >>> memory size. >>> >> +1, makes sense to keep just one of the above two. >>>> Setup & procedure - >>>> Total NUMA Node Memory ~ 15 GB (All guests are run on a single NUMA node) >>>> Guest Memory = 6GB >>>> Number of CPUs in the guest = 4 >>>> Process = 3 Guests are launched and the ‘memhog 6G’ execution time is monitored >>>> one after the other in each of them. >>>> Host swap = 4GB >>>> >>>> Performance Analysis: >>>> 1. will-it-scale's page_faul1 >>>> Setup - >>>> Guest Memory = 6GB >>>> Number of cores = 24 >>>> >>>> Unmodified kernel - >>>> 0,0,100,0,100,0 >>>> 1,514453,95.84,519502,95.83,519502 >>>> 2,991485,91.67,932268,91.68,1039004 >>>> 3,1381237,87.36,1264214,87.64,1558506 >>>> 4,1789116,83.36,1597767,83.88,2078008 >>>> 5,2181552,79.20,1889489,80.08,2597510 >>>> 6,2452416,75.05,2001879,77.10,3117012 >>>> 7,2671047,70.90,2263866,73.22,3636514 >>>> 8,2930081,66.75,2333813,70.60,4156016 >>>> 9,3126431,62.60,2370108,68.28,4675518 >>>> 10,3211937,58.44,2454093,65.74,5195020 >>>> 11,3162172,54.32,2450822,63.21,5714522 >>>> 12,3154261,50.14,2272290,58.98,6234024 >>>> 13,3115174,46.02,2369679,57.74,6753526 >>>> 14,3150511,41.86,2470837,54.02,7273028 >>>> 15,3134158,37.71,2428129,51.98,7792530 >>>> 16,3143067,33.57,2340469,49.54,8312032 >>>> 17,3112457,29.43,2263627,44.81,8831534 >>>> 18,3089724,25.29,2181879,38.69,9351036 >>>> 19,3076878,21.15,2236505,40.01,9870538 >>>> 20,3091978,16.95,2266327,35.00,10390040 >>>> 21,3082927,12.84,2172578,28.12,10909542 >>>> 22,3055282,8.73,2176269,29.14,11429044 >>>> 23,3081144,4.56,2138442,24.87,11948546 >>>> 24,3075509,0.45,2173753,21.62,12468048 >>>> >>>> page hinting - >>>> 0,0,100,0,100,0 >>>> 1,491683,95.83,494366,95.82,494366 >>>> 2,988415,91.67,919660,91.68,988732 >>>> 3,1344829,87.52,1244608,87.69,1483098 >>>> 4,1797933,83.37,1625797,83.70,1977464 >>>> 5,2179009,79.21,1881534,80.13,2471830 >>>> 6,2449858,75.07,2078137,76.82,2966196 >>>> 7,2732122,70.90,2178105,73.75,3460562 >>>> 8,2910965,66.75,2340901,70.28,3954928 >>>> 9,3006665,62.61,2353748,67.91,4449294 >>>> 10,3164752,58.46,2377936,65.08,4943660 >>>> 11,3234846,54.32,2510149,63.14,5438026 >>>> 12,3165477,50.17,2412007,59.91,5932392 >>>> 13,3141457,46.05,2421548,57.85,6426758 >>>> 14,3135839,41.90,2378021,53.81,6921124 >>>> 15,3109113,37.75,2269290,51.76,7415490 >>>> 16,3093613,33.62,2346185,48.73,7909856 >>>> 17,3086542,29.49,2352140,46.19,8404222 >>>> 18,3048991,25.36,2217144,41.52,8898588 >>>> 19,2965500,21.18,2313614,38.18,9392954 >>>> 20,2928977,17.05,2175316,35.67,9887320 >>>> 21,2896667,12.91,2141311,28.90,10381686 >>>> 22,3047782,8.76,2177664,28.24,10876052 >>>> 23,2994503,4.58,2160976,22.97,11370418 >>>> 24,3038762,0.47,2053533,22.39,11864784 >>>> >>>> bubble-hinting v1 - >>>> 0,0,100,0,100,0 >>>> 1,515272,95.83,492355,95.81,515272 >>>> 2,985903,91.66,919653,91.68,1030544 >>>> 3,1475300,87.51,1353723,87.65,1545816 >>>> 4,1783938,83.36,1586307,83.78,2061088 >>>> 5,2093307,79.20,1867395,79.95,2576360 >>>> 6,2441370,75.05,2055421,76.65,3091632 >>>> 7,2650471,70.89,2246014,72.93,3606904 >>>> 8,2926782,66.75,2333601,70.41,4122176 >>>> 9,3107617,62.60,2383112,68.46,4637448 >>>> 10,3192332,58.44,2441626,65.84,5152720 >>>> 11,3268043,54.32,2235964,62.92,5667992 >>>> 12,3191105,50.18,2449045,60.49,6183264 >>>> 13,3145317,46.05,2377317,57.80,6698536 >>>> 14,3161552,41.91,2395814,53.26,7213808 >>>> 15,3140443,37.77,2333200,51.42,7729080 >>>> 16,3130866,33.65,2150967,46.11,8244352 >>>> 17,3112894,29.52,2372068,45.93,8759624 >>>> 18,3078424,25.39,2336211,39.85,9274896 >>>> 19,3036457,21.27,2224821,35.25,9790168 >>>> 20,3046330,17.13,2199755,37.43,10305440 >>>> 21,2981130,12.98,2214862,28.67,10820712 >>>> 22,3017481,8.84,2195996,29.69,11335984 >>>> 23,2979906,4.68,2173395,25.90,11851256 >>>> 24,2971170,0.52,2134311,21.89,12366528 >>> Okay, so this doesn't match up with the results you gave me last time >>> (https://lore.kernel.org/lkml/afac6f92-74f5-4580-0303-12b7374e5011@xxxxxxxxxx/), >>> and actually more closely matches what I was expecting to see. The >>> bubble-hinting patches are performing within a few percent of what the >>> baseline kernel was doing. >> Interestingly even with an unmodified kernel with every fresh boot, I >> observed a certain amount of variability in the results which I stated >> below. >>> I am assuming the results from before had >>> some additional debugging enabled for the bubble-hinting test that >>> wasn't enabled for the other ones. >> Nope, I had debugging options enabled for all the cases. This time >> around I disabled all the debug options. > We can agree to disagree I guess. Those debugging options had reduced > the throughput by over 30% on the guest kernel in my test runs. I was > never able to reproduce the data you reported as enabling the same > debug features on an unmodified kernel had reduced the throughput for > the test just the same as it did for the bubble hinting version. Were > you running the debug options on the host kernel or the guest? In the guest. Do the results which I shared without debug options, match with what you have? I am also curious to know if you see any variability in the results of page_fault1 for an unmodified kernel with every fresh boot? If so how often? > I > suppose it is possible that having those debug options enabled on the > host might trigger similar behavior to what you reported since you > were using MADV_FREE versus MADV_DONTNEED so you wouldn't have to > reallocate the pages and could circumvent the page allocation > debugging. > >>>> Conclusion - >>>> For an unmodified kernel, with every fresh boot, there is 3-4% delta observed >>>> in the results wrt the numbers mentioned above. For both bubble-hinting and >>>> page-hinting, there was no noticeable degradation observed other than the >>>> expected variability mentioned earlier. >>>> >>>> Page hinting vs bubble hinting: >>>> From the benefits and performance perspective, both solutions look quite similar >>>> so far. However, unlike bubble-hinting which is more invasive, the overall core >>>> mm changes required for page hinting are minimal. >>>> >>>> [1] https://lkml.org/lkml/2019/6/19/926 >>> So I think I called it out in the review of the patch but I think we >>> may want to see what happens if we increase the size of the memory in >>> the guest to something more like 64G or larger. My main concern is >>> that as we increase the size of memory the walk through the bitmap is >>> going to become more and more expensive and I am worried that at some >>> point it will start impacting the results. >> Ok, I can try that scenario. >> >> >> >> -- >> Thanks >> Nitesh >> -- Thanks Nitesh
