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Wed, 05 Nov 2025 02:18:14 -0800 (PST) Date: Wed, 5 Nov 2025 02:18:11 -0800 From: Breno Leitao To: Pratyush Yadav Cc: Changyuan Lyu , rppt@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, anthony.yznaga@oracle.com, arnd@arndb.de, ashish.kalra@amd.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, corbet@lwn.net, dave.hansen@linux.intel.com, devicetree@vger.kernel.org, dwmw2@infradead.org, ebiederm@xmission.com, graf@amazon.com, hpa@zytor.com, jgowans@amazon.com, kexec@lists.infradead.org, krzk@kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, luto@kernel.org, mark.rutland@arm.com, mingo@redhat.com, pasha.tatashin@soleen.com, pbonzini@redhat.com, peterz@infradead.org, robh@kernel.org, rostedt@goodmis.org, saravanak@google.com, skinsburskii@linux.microsoft.com, tglx@linutronix.de, thomas.lendacky@amd.com, will@kernel.org, x86@kernel.org Subject: Re: [PATCH v8 01/17] memblock: add MEMBLOCK_RSRV_KERN flag Message-ID: References: <20250509074635.3187114-1-changyuanl@google.com> <20250509074635.3187114-2-changyuanl@google.com> <2ege2jfbevtunhxsnutbzde7cqwgu5qbj4bbuw2umw7ke7ogcn@5wtskk4exzsi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2A52780009 X-Stat-Signature: ngn96ebjnh4uhn9co4ngg43nd5wm3cyx X-Rspam-User: X-HE-Tag: 1762337896-681842 X-HE-Meta: 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 ziJZpNtA K8srJiIRUlF6XisFv93Wzaj+tOn/xLfeamBPDWTgNSTpU5pDkFdGNvvF67hD4142rfVETY9KThzl/8NspHZFUxM+tg6S3dfP3Cd+uJfm4t0mFEERsIn18BC7hpdAV2xRGUz1aIImTVQwEEX1Vo0HLpvcSqEg2CTh9gZgoPPCeJDvs7YzL0Qnbo1/Pk3Rx5gQztIhBzG1Jlhevrsl1/cPAj1wxwajkcg9YYU3yghConeRI2LW0gVEiBqRDJ24oDOQOdtA5QPz4XdKbYLILGBOJ2an2zMWvy/xydT7A2fxxYCmqtgrGdRxp4ccwZaai58UynDUnZ04SmkJtPny+p2jhLIZP7M88PFZPQzRpkLAS+Ry/cGPv+A1KIiAN/v32w04XQeJKAJ9cLQOFq1wLfvaS16cbIge6qgqMMSvWr9S89ZJ8vk+2zEGG1njEGNQs0GhCWle3CObqWBYtQye2VgKKsWmNu5NF1MgiGjYV 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: Hello Pratyush, On Tue, Oct 14, 2025 at 03:10:37PM +0200, Pratyush Yadav wrote: > On Tue, Oct 14 2025, Breno Leitao wrote: > > On Mon, Oct 13, 2025 at 06:40:09PM +0200, Pratyush Yadav wrote: > >> On Mon, Oct 13 2025, Pratyush Yadav wrote: > >> > > >> > I suppose this would be useful. I think enabling memblock debug prints > >> > would also be helpful (using the "memblock=debug" commandline parameter) > >> > if it doesn't impact your production environment too much. > >> > >> Actually, I think "memblock=debug" is going to be the more useful thing > >> since it would also show what function allocated the overlapping range > >> and the flags it was allocated with. > >> > >> On my qemu VM with KVM, this results in around 70 prints from memblock. > >> So it adds a bit of extra prints but nothing that should be too > >> disrupting I think. Plus, only at boot so the worst thing you get is > >> slightly slower boot times. > > > > Unfortunately this issue is happening on production systems, and I don't > > have an easy way to reproduce it _yet_. > > > > At the same time, "memblock=debug" has two problems: > > > > 1) It slows the boot time as you suggested. Boot time at large > > environments is SUPER critical and time sensitive. It is a bit > > weird, but it is common for machines in production to kexec > > _thousands_ of times, and kexecing is considered downtime. > > I don't know if it would make a real enough difference on boot times, > only that it should theoretically affect it, mainly if you are using > serial for dmesg logs. Anyway, that's your production environment so you > know best. > > > > > This would be useful if I find some hosts getting this issue, and > > then I can easily enable the extra information to collect what > > I need, but, this didn't pan out because the hosts I got > > `memblock=debug` didn't collaborate. > > > > 2) "memblock=debug" is verbose for all cases, which also not necessary > > the desired behaviour. I am more interested in only being verbose > > when there is a known problem. I am still interested in this problem, and I finally found a host that constantly reproduce the issue and I was able to get `memblock=debug` cmdline. I am running 6.18-rc4 with some debug options enabled. DMA-API: exceeded 7 overlapping mappings of cacheline 0x0000000006d6e400 WARNING: CPU: 58 PID: 828 at kernel/dma/debug.c:463 add_dma_entry+0x2e4/0x330 pc : add_dma_entry+0x2e4/0x330 lr : add_dma_entry+0x2e4/0x330 sp : ffff8000b036f7f0 x29: ffff8000b036f800 x28: 0000000000000001 x27: 0000000000000008 x26: ffff8000835f7fb8 x25: ffff8000835f7000 x24: ffff8000835f7ee0 x23: 0000000000000000 x22: 0000000006d6e400 x21: 0000000000000000 x20: 0000000006d6e400 x19: ffff0003f70c1100 x18: 00000000ffffffff x17: ffff80008019a2d8 x16: ffff80008019a08c x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000820 x12: ffff00011faeaf00 x11: 0000000000000000 x10: ffff8000834633d8 x9 : ffff8000801979d4 x8 : 00000000fffeffff x7 : ffff8000834633d8 x6 : 0000000000000000 x5 : 00000000000bfff4 x4 : 0000000000000000 x3 : ffff0001075eb7c0 x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0001075eb7c0 Call trace: add_dma_entry+0x2e4/0x330 (P) debug_dma_map_phys+0xc4/0xf0 dma_map_phys (/home/leit/Devel/upstream/./include/linux/dma-direct.h:138 /home/leit/Devel/upstream/kernel/dma/direct.h:102 /home/leit/Devel/upstream/kernel/dma/mapping.c:169) dma_map_page_attrs (/home/leit/Devel/upstream/kernel/dma/mapping.c:387) blk_dma_map_direct.isra.0 (/home/leit/Devel/upstream/block/blk-mq-dma.c:102) blk_dma_map_iter_start (/home/leit/Devel/upstream/block/blk-mq-dma.c:123 /home/leit/Devel/upstream/block/blk-mq-dma.c:196) blk_rq_dma_map_iter_start (/home/leit/Devel/upstream/block/blk-mq-dma.c:228) nvme_prep_rq+0xb8/0x9b8 nvme_queue_rq+0x44/0x1b0 blk_mq_dispatch_rq_list (/home/leit/Devel/upstream/block/blk-mq.c:2129) __blk_mq_sched_dispatch_requests (/home/leit/Devel/upstream/block/blk-mq-sched.c:314) blk_mq_sched_dispatch_requests (/home/leit/Devel/upstream/block/blk-mq-sched.c:329) blk_mq_run_work_fn (/home/leit/Devel/upstream/block/blk-mq.c:219 /home/leit/Devel/upstream/block/blk-mq.c:231) process_one_work (/home/leit/Devel/upstream/kernel/workqueue.c:991 /home/leit/Devel/upstream/kernel/workqueue.c:3213) worker_thread (/home/leit/Devel/upstream/./include/linux/list.h:163 /home/leit/Devel/upstream/./include/linux/list.h:191 /home/leit/Devel/upstream/./include/linux/list.h:319 /home/leit/Devel/upstream/kernel/workqueue.c:1153 /home/leit/Devel/upstream/kernel/workqueue.c:1205 /home/leit/Devel/upstream/kernel/workqueue.c:3426) kthread (/home/leit/Devel/upstream/kernel/kthread.c:386 /home/leit/Devel/upstream/kernel/kthread.c:457) ret_from_fork (/home/leit/Devel/upstream/entry.S:861) Looking at memblock debug logs, I haven't seen anything related to 0x0000000006d6e400. I got the output of `dmesg | grep memblock` in, in case you are curious: https://github.com/leitao/debug/blob/main/pastebin/memblock/dmesg_grep_memblock.txt Thanks --breno