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[173.68.57.129]) by smtp.gmail.com with ESMTPSA id w9sm497119qko.71.2021.12.14.11.18.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Dec 2021 11:18:51 -0800 (PST) Date: Tue, 14 Dec 2021 14:18:50 -0500 From: Dennis Zhou To: Geert Uytterhoeven Cc: Vladimir Murzin , linux-arch-owner@vger.kernel.org, Linux MM , Tejun Heo , Christoph Lameter , Andrew Morton , Nicholas Piggin , Christoph Hellwig , Arnd Bergmann , Linux-sh list , Rich Felker , linux-riscv Subject: Re: [PATCH] percpu: km: ensure it is used with NOMMU (either UP or SMP) Message-ID: References: <20211130172954.129587-1-vladimir.murzin@arm.com> <20211130172954.129587-2-vladimir.murzin@arm.com> <8c2b4666-cf13-3735-be1e-b8a1c71df113@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: anskdinsincctxcrgxzbsscgqik49m3s Authentication-Results: imf17.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=kernel.org (policy=none); spf=pass (imf17.hostedemail.com: domain of dennisszhou@gmail.com designates 209.85.222.174 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A246D40012 X-HE-Tag: 1639509527-99033 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 Tue, Dec 14, 2021 at 08:02:58PM +0100, Geert Uytterhoeven wrote: > Hi Dennis, > > On Tue, Dec 14, 2021 at 6:26 PM Dennis Zhou wrote: > > On Tue, Dec 14, 2021 at 05:29:22PM +0100, Geert Uytterhoeven wrote: > > > On Wed, Dec 1, 2021 at 12:53 PM Vladimir Murzin wrote: > > > > On 11/30/21 5:41 PM, Dennis Zhou wrote: > > > > > On Tue, Nov 30, 2021 at 05:29:54PM +0000, Vladimir Murzin wrote: > > > > >> Currently, NOMMU pull km allocator via !SMP dependency because most of > > > > >> them are UP, yet for SMP+NOMMU vm allocator gets pulled which: > > > > >> > > > > >> * may lead to broken build [1] > > > > >> * ...or not working runtime due to [2] > > > > >> > > > > >> It looks like SMP+NOMMU case was overlooked in bbddff054587 ("percpu: > > > > >> use percpu allocator on UP too") so restore that. > > > > >> > > > > >> [1] > > > > >> For ARM SMP+NOMMU (R-class cores) > > > > >> > > > > >> arm-none-linux-gnueabihf-ld: mm/percpu.o: in function `pcpu_post_unmap_tlb_flush': > > > > >> mm/percpu-vm.c:188: undefined reference to `flush_tlb_kernel_range' > > > > >> > > > > >> [2] > > > > >> static inline > > > > >> int vmap_pages_range_noflush(unsigned long addr, unsigned long end, > > > > >> pgprot_t prot, struct page **pages, unsigned int page_shift) > > > > >> { > > > > >> return -EINVAL; > > > > >> } > > > > >> > > > > >> Signed-off-by: Vladimir Murzin > > > > >> --- > > > > >> mm/Kconfig | 3 +-- > > > > >> 1 file changed, 1 insertion(+), 2 deletions(-) > > > > >> > > > > >> diff --git a/mm/Kconfig b/mm/Kconfig > > > > >> index d16ba92..66331e0 100644 > > > > >> --- a/mm/Kconfig > > > > >> +++ b/mm/Kconfig > > > > >> @@ -425,9 +425,8 @@ config THP_SWAP > > > > >> # UP and nommu archs use km based percpu allocator > > > > >> # > > > > >> config NEED_PER_CPU_KM > > > > >> - depends on !SMP > > > > >> bool > > > > >> - default y > > > > >> + default !SMP || !MMU > > > > >> > > > > > > > > > > Should this be `depends on !SMP || !MMU` with default yes? Because with > > > > > SMP && MMU, it shouldn't be an option to run with percpu-km. > > > > > > > > IIUC these are equivalent, truth table would not change if is under "depends" > > > > or "default" > > > > > > > > SMP MMU NEED_PER_CPU_KM > > > > y y !y || !y => n || n => n > > > > y n !y || !n => n || y => y > > > > n y !n || !y => y || n => y > > > > n n !n || !n => y || y => y > > > > > > > > > > > > > >> config CLEANCACHE > > > > >> bool "Enable cleancache driver to cache clean pages if tmem is present" > > > > >> -- > > > > >> 2.7.4 > > > > >> > > > > > > > > > > It's interesting to me that this is all coming up at once. Earlier this > > > > > month I had the same conversation with people involved with sh [1]. > > > > > > > > > > [1] https://lore.kernel.org/linux-sh/YY7tp5attRyK42Zk@fedora/ > > > > > > > > > > I can pull this shortly once I see whatever happened to linux-sh. > > > > > > > > Ahh, good to know! Adding SH folks here (start of discussion [0]). I see you came > > > > to the same conclusion, right? > > > > > > > > IIRC, RISC-V also have SMP+NOMMU, so adding them as well. > > > > > > I had seen the j-Core thread, but completely forgot about > > > Canaan K210 (RV64 SMP+NOMMU). > > > > > > This became commit 3583521aabac76e5 ("percpu: km: ensure it is used > > > with NOMMU (either UP or SMP)"). And now booting K210 prints: > > > > > > percpu: wasting 10 pages per chunk > > > > > > a) Is this bad? > > > > It's not great.. Can you share the line on boot with the following > > prefix: pcpu-alloc [1]. > > There are no such lines. > "make mm/percpu.i mm/percpu.s" and inspecting the generated files, > and vmlinux, proves the code is there. But apparently it's not called. > > So there may be no issue on my system? > I might be missing something, but that can't be right. Percpu calls pcpu_dump_alloc_info() from pcpu_setup_first_chunk() which is called by both embed/page first chunk code. Ummm. That can't be right. Percpu call pcpu_dump_alloc_info() from pcpu_setup_first_chunk() which everyone should call. On my machine: $ dmesg | grep "pcpu-alloc" [ 0.065118] pcpu-alloc: s184320 r8192 d28672 u262144 alloc=1*2097152 Thanks, Dennis