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Thu, 07 Aug 2025 10:47:15 -0700 (PDT) MIME-Version: 1.0 References: <202508071609.4e743d7c-lkp@intel.com> <9e3a59b2-11c0-43ca-aff3-414091f04aa4@lucifer.local> In-Reply-To: From: Jann Horn Date: Thu, 7 Aug 2025 19:46:39 +0200 X-Gm-Features: Ac12FXz0pqhZ5ZXNMYXrgkg69OVAPBJ7j_8d24_PRsIXf3jxPz6zdWEIncqLCrg Message-ID: Subject: Re: [linus:master] [mm] f822a9a81a: stress-ng.bigheap.realloc_calls_per_sec 37.3% regression To: Lorenzo Stoakes Cc: kernel test robot , Dev Jain , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Barry Song , Pedro Falcato , Anshuman Khandual , Bang Li , Baolin Wang , bibo mao , David Hildenbrand , Hugh Dickins , Ingo Molnar , Lance Yang , Liam Howlett , Matthew Wilcox , Peter Xu , Qi Zheng , Ryan Roberts , Vlastimil Babka , Yang Shi , Zi Yan , linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: d3tnt3rx3dwob9x8nog3n54oxg5a5jx4 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 953A81A0005 X-Rspam-User: X-HE-Tag: 1754588837-527572 X-HE-Meta: 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 YrF7aevx mZMjJTHlEXiq6PFY6eA6S9n+yWep/tXr2Ky/C2HM9Of1V0vSXQbaVMon/OLSOErCYc7fZXa3BLs9MYzoGxWFpRkjrXy8isUFMe/hRqjEKHRuMFTpv1Xyh8/UmC8vb9GFgl+Jn14YET7QRs30UoQCYS3oP7cwvNTkaLtsDFPjqSvp4uvCn2qYCnH/Mb/J9IoLccQjddoiwoUxgexxT1Wvp0CyvW977fG2uuR6UKET7epbh/x+LHV3VHHGI/245KGATyq17oMEUVR2ccabv2nJrdTJ2WPJYWOSJbpu2ZNIAg/TiMDrp4pal7nxU3w== 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: List-Subscribe: List-Unsubscribe: On Thu, Aug 7, 2025 at 7:41=E2=80=AFPM Lorenzo Stoakes wrote: > On Thu, Aug 07, 2025 at 07:37:38PM +0200, Jann Horn wrote: > > On Thu, Aug 7, 2025 at 10:28=E2=80=AFAM Lorenzo Stoakes > > wrote: > > > On Thu, Aug 07, 2025 at 04:17:09PM +0800, kernel test robot wrote: > > > > 94dab12d86cf77ff f822a9a81a31311d67f260aea96 > > > > ---------------- --------------------------- > > > > %stddev %change %stddev > > > > \ | \ > > > > 13777 =C4=85 37% +45.0% 19979 =C4=85 27% numa-vmstat= .node1.nr_slab_reclaimable > > > > 367205 +2.3% 375703 vmstat.system.in > > > > 55106 =C4=85 37% +45.1% 79971 =C4=85 27% numa-meminf= o.node1.KReclaimable > > > > 55106 =C4=85 37% +45.1% 79971 =C4=85 27% numa-meminf= o.node1.SReclaimable > > > > 559381 -37.3% 350757 stress-ng.bigheap.rea= lloc_calls_per_sec > > > > 11468 +1.2% 11603 stress-ng.time.system= _time > > > > 296.25 +4.5% 309.70 stress-ng.time.user_t= ime > > > > 0.81 =C4=85187% -100.0% 0.00 perf-sched.sch_d= elay.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0 > > > > 9.36 =C4=85165% -100.0% 0.00 perf-sched.sch_d= elay.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0 > > > > 0.81 =C4=85187% -100.0% 0.00 perf-sched.wait_= time.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0 > > > > 9.36 =C4=85165% -100.0% 0.00 perf-sched.wait_= time.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0 > > > > 5.50 =C4=85 17% +390.9% 27.00 =C4=85 56% perf-c2c.DR= AM.local > > > > 388.50 =C4=85 10% +114.7% 834.17 =C4=85 33% perf-c2c.DR= AM.remote > > > > 1214 =C4=85 13% +107.3% 2517 =C4=85 31% perf-c2c.HI= TM.local > > > > 135.00 =C4=85 19% +130.9% 311.67 =C4=85 32% perf-c2c.HI= TM.remote > > > > 1349 =C4=85 13% +109.6% 2829 =C4=85 31% perf-c2c.HI= TM.total > > > > > > Yeah this also looks pretty consistent too... > > > > FWIW, HITM hat different meanings depending on exactly which > > microarchitecture that test happened on; the message says it is from > > Sapphire Rapids, which is a successor of Ice Lake, so HITM is less > > meaningful than if it came from a pre-IceLake system (see > > https://lore.kernel.org/all/CAG48ez3RmV6SsVw9oyTXxQXHp3rqtKDk2qwJWo9TGv= XCq7Xr-w@mail.gmail.com/). > > > > To me those numbers mainly look like you're accessing a lot more > > cache-cold data. (On pre-IceLake they would indicate cacheline > > bouncing, but I guess here they probably don't.) And that makes sense, > > since before the patch, this path was just moving PTEs around without > > looking at the associated pages/folios; basically more or less like a > > memcpy() on x86-64. But after the patch, for every 8 bytes that you > > copy, you have to load a cacheline from the vmemmap to get the page. > > Yup this is representative of what my investigation is showing. > > I've narrowed it down but want to wait to report until I'm sure... > > But yeah we're doing a _lot_ more work. > > I'm leaning towards disabling except for arm64 atm tbh, seems mremap is > especially sensitive to this (I found issues with this with my abortive m= remap > anon merging stuff too, but really expected it there...) Another approach would be to always read and write PTEs in contpte-sized chunks here, without caring whether they're actually contiguous or whatever, or something along those lines.