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[209.85.222.54]) by smtp.gmail.com with ESMTPSA id h10sm39620vsl.34.2021.12.14.08.29.34 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Dec 2021 08:29:34 -0800 (PST) Received: by mail-ua1-f54.google.com with SMTP id n9so16812970uaq.10 for ; Tue, 14 Dec 2021 08:29:34 -0800 (PST) X-Received: by 2002:a05:6102:21dc:: with SMTP id r28mr6178703vsg.57.1639499373849; Tue, 14 Dec 2021 08:29:33 -0800 (PST) MIME-Version: 1.0 References: <20211130172954.129587-1-vladimir.murzin@arm.com> <20211130172954.129587-2-vladimir.murzin@arm.com> <8c2b4666-cf13-3735-be1e-b8a1c71df113@arm.com> In-Reply-To: <8c2b4666-cf13-3735-be1e-b8a1c71df113@arm.com> From: Geert Uytterhoeven Date: Tue, 14 Dec 2021 17:29:22 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] percpu: km: ensure it is used with NOMMU (either UP or SMP) To: Vladimir Murzin , Dennis Zhou Cc: 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 Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5CD654000D X-Stat-Signature: 1j9hscixf9m7ejm7knnt3i7hcoz8z5i1 Authentication-Results: imf07.hostedemail.com; dkim=none; spf=pass (imf07.hostedemail.com: domain of geert.uytterhoeven@gmail.com designates 209.85.222.52 as permitted sender) smtp.mailfrom=geert.uytterhoeven@gmail.com; dmarc=none X-HE-Tag: 1639499376-686643 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: Hi Vladimir and Dennis, 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? b) What exactly was this fixing, and how would I trigger the bad case on K210 before, if it was affected at all? > > [0] https://lore.kernel.org/linux-mm/20211130172954.129587-1-vladimir.murzin@arm.com/T/ Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds