Re: [RFC][PATCH v11 0/2] mm: Support for page hinting

[Nitesh Narayan Lal]

On 7/11/19 11:08 AM, Alexander Duyck wrote:
> On Thu, Jul 11, 2019 at 8:04 AM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote:
>>
>> 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 âmemhog 6Gâ 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 see some variability, but not much. Usually it can vary by +/- 5% or
> so.
+1
>  What I have been doing is collecting multiple runs, working out
> the average, and then comparing that against an average with the
> patches applied.
Yeah, I didn't share the average values but I do the same.
I just wanted to mention the variability so that there is no confusion
if later the value comes out to be in the range of +/- 3-4%.
>
> One other thing you can probably do to limit the variability would be
> to look at disabling any power management features on the system. One
> thing you could be seeing is the effect of the CPU enabling turbo mode
> or going into sleep states if idle. That can easily throw the numbers
> around quite a bit.
The variability you mentioned, was it after disabling these options?
-- 
Thanks
Nitesh