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dmarc=pass action=none header.from=fb.com; dkim=pass header.d=fb.com; arc=none Authentication-Results: linux.ibm.com; dkim=none (message not signed) header.d=none;linux.ibm.com; dmarc=none action=none header.from=fb.com; Received: from BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) by SJ0PR15MB4357.namprd15.prod.outlook.com (2603:10b6:a03:380::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4042.16; Fri, 16 Apr 2021 18:34:21 +0000 Received: from BYAPR15MB4136.namprd15.prod.outlook.com ([fe80::2c3d:df54:e11c:ee99]) by BYAPR15MB4136.namprd15.prod.outlook.com ([fe80::2c3d:df54:e11c:ee99%6]) with mapi id 15.20.4020.025; Fri, 16 Apr 2021 18:34:21 +0000 Date: Fri, 16 Apr 2021 11:34:16 -0700 From: Roman Gushchin To: Pratik Sampat CC: Dennis Zhou , Tejun Heo , Christoph Lameter , Andrew Morton , Vlastimil Babka , , , Subject: Re: [PATCH v3 0/6] percpu: partial chunk depopulation Message-ID: References: <20210408035736.883861-1-guro@fb.com> <25c78660-9f4c-34b3-3a05-68c313661a46@linux.ibm.com> <7a001bf6-5708-fb04-4970-367d9845ccb9@linux.ibm.com> <8ea7c616-95e8-e391-5373-ebaf10836d2c@linux.ibm.com> Content-Type: text/plain; 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identity=mailfrom; envelope-from=""; helo=mx0a-00082601.pphosted.com; client-ip=67.231.145.42 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618598058-555867 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 16, 2021 at 11:57:03PM +0530, Pratik Sampat wrote: >=20 >=20 > On 16/04/21 10:43 pm, Roman Gushchin wrote: > > On Fri, Apr 16, 2021 at 08:58:33PM +0530, Pratik Sampat wrote: > > > Hello Dennis, > > >=20 > > > I apologize for the clutter of logs before, I'm pasting the logs of= before and > > > after the percpu test in the case of the patchset being applied on = 5.12-rc6 and > > > the vanilla kernel 5.12-rc6. > > >=20 > > > On 16/04/21 7:48 pm, Dennis Zhou wrote: > > > > Hello, > > > >=20 > > > > On Fri, Apr 16, 2021 at 06:26:15PM +0530, Pratik Sampat wrote: > > > > > Hello Roman, > > > > >=20 > > > > > I've tried the v3 patch series on a POWER9 and an x86 KVM setup= . > > > > >=20 > > > > > My results of the percpu_test are as follows: > > > > > Intel KVM 4CPU:4G > > > > > Vanilla 5.12-rc6 > > > > > # ./percpu_test.sh > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 1952 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 219648 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 219648 kB > > > > >=20 > > > > > 5.12-rc6 + with patchset applied > > > > > # ./percpu_test.sh > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 2080 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 219712 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 72672 kB > > > > >=20 > > > > > I'm able to see improvement comparable to that of what you're s= ee too. > > > > >=20 > > > > > However, on POWERPC I'm unable to reproduce these improvements = with the patchset in the same configuration > > > > >=20 > > > > > POWER9 KVM 4CPU:4G > > > > > Vanilla 5.12-rc6 > > > > > # ./percpu_test.sh > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 5888 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 118272 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 118272 kB > > > > >=20 > > > > > 5.12-rc6 + with patchset applied > > > > > # ./percpu_test.sh > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 6144 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 119040 kB > > > > > Percpu:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 119040 kB > > > > >=20 > > > > > I'm wondering if there's any architectural specific code that n= eeds plumbing > > > > > here? > > > > >=20 > > > > There shouldn't be. Can you send me the percpu_stats debug output= before > > > > and after? > > > I'll paste the whole debug stats before and after here. > > > 5.12-rc6 + patchset > > > -----BEFORE----- > > > Percpu Memory Statistics > > > Allocation Info: > >=20 > > Hm, this looks highly suspicious. Here is your stats in a more compac= t form: > >=20 > > Vanilla > >=20 > > nr_alloc : 9038 nr_alloc : = 97046 > > nr_dealloc : 6992 nr_dealloc : 94= 237 > > nr_cur_alloc : 2046 nr_cur_alloc : 2= 809 > > nr_max_alloc : 2178 nr_max_alloc : 90= 054 > > nr_chunks : 3 nr_chunks : = 11 > > nr_max_chunks : 3 nr_max_chunks : = 47 > > min_alloc_size : 4 min_alloc_size : = 4 > > max_alloc_size : 1072 max_alloc_size : 1= 072 > > empty_pop_pages : 5 empty_pop_pages : = 29 > >=20 > >=20 > > Patched > >=20 > > nr_alloc : 9040 nr_alloc : = 97048 > > nr_dealloc : 6994 nr_dealloc : 95= 002 > > nr_cur_alloc : 2046 nr_cur_alloc : 2= 046 > > nr_max_alloc : 2208 nr_max_alloc : 90= 054 > > nr_chunks : 3 nr_chunks : = 48 > > nr_max_chunks : 3 nr_max_chunks : = 48 > > min_alloc_size : 4 min_alloc_size : = 4 > > max_alloc_size : 1072 max_alloc_size : 1= 072 > > empty_pop_pages : 12 empty_pop_pages : = 61 > >=20 > >=20 > > So it looks like the number of chunks got bigger, as well as the numb= er of > > empty_pop_pages? This contradicts to what you wrote, so can you, plea= se, make > > sure that the data is correct and we're not messing two cases? > >=20 > > So it looks like for some reason sidelined (depopulated) chunks are n= ot getting > > freed completely. But I struggle to explain why the initial empty_pop= _pages is > > bigger with the same amount of chunks. > >=20 > > So, can you, please, apply the following patch and provide an updated= statistics? >=20 > Unfortunately, I'm not completely well versed in this area, but yes the= empty > pop pages number doesn't make sense to me either. >=20 > I re-ran the numbers trying to make sure my experiment setup is sane bu= t > results remain the same. >=20 > Vanilla > nr_alloc : 9040 nr_alloc : = 97048 > nr_dealloc : 6994 nr_dealloc : 9440= 4 > nr_cur_alloc : 2046 nr_cur_alloc : 264= 4 > nr_max_alloc : 2169 nr_max_alloc : 9005= 4 > nr_chunks : 3 nr_chunks : 1= 0 > nr_max_chunks : 3 nr_max_chunks : 4= 7 > min_alloc_size : 4 min_alloc_size : = 4 > max_alloc_size : 1072 max_alloc_size : 107= 2 > empty_pop_pages : 4 empty_pop_pages : 3= 2 >=20 > With the patchset + debug patch the results are as follows: > Patched >=20 > nr_alloc : 9040 nr_alloc : = 97048 > nr_dealloc : 6994 nr_dealloc : 9434= 9 > nr_cur_alloc : 2046 nr_cur_alloc : 269= 9 > nr_max_alloc : 2194 nr_max_alloc : 9005= 4 > nr_chunks : 3 nr_chunks : 4= 8 > nr_max_chunks : 3 nr_max_chunks : 4= 8 > min_alloc_size : 4 min_alloc_size : = 4 > max_alloc_size : 1072 max_alloc_size : 107= 2 > empty_pop_pages : 12 empty_pop_pages : 5= 4 >=20 > With the extra tracing I can see 39 entries of "Chunk (sidelined)" > after the test was run. I don't see any entries for "Chunk (to depopula= te)" >=20 > I've snipped the results of slidelined chunks because they went on for = ~600 > lines, if you need the full logs let me know. Yes, please! That's the most interesting part!