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bh=SsEFykTTr1Y+kZYyRqrdoefiJQaCTMcgpE7uD+V55Ow=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=OWDqbvWlIm7OcMQaGlT+EtXnC54BfSzGWgOzgp5j/7ydS/dewMezjQOwRKCHPIOHe TL051HGjO/RDOZjAL0Y+hLp1zKulj0+SdesJUstAg7+V1AYaACvbwkWZOFwyOLoquG awMoPUgNJ8SVHbU98ceJNJxa+JjwbY8tOzQtF2AMzz0d8qRkmgx9DpmFFTa3dZ5zl1 zp0pnAAu8cf8xuN/gn/mMGXQo3SsfxZT5anmzHl+FPItlPFjQv/g+hIRFpHqmMMIDZ ykHwy9qcqwBUlDwGHk7LUvgSux9HeyHuTv2yp/sv4ee1+ADOPUQeky9Us0pLZNu0XU NMy7pb6+v+YLA== From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= To: Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org Cc: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@rivosinc.com, Alexandre Ghiti , Joerg Roedel Subject: Re: [PATCH] riscv: mm: Pre-allocate PGD entries vmalloc/modules area In-Reply-To: <20230529180023.289904-1-bjorn@kernel.org> References: <20230529180023.289904-1-bjorn@kernel.org> Date: Tue, 30 May 2023 08:37:17 +0200 Message-ID: <871qiyfhpe.fsf@all.your.base.are.belong.to.us> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: bads7rpnnmw574wxtk3zmzhazoba4z8x X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 745E3180002 X-HE-Tag: 1685428643-336109 X-HE-Meta: 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 JUGLTEGK 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 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: Bj=C3=B6rn T=C3=B6pel writes: > From: Bj=C3=B6rn T=C3=B6pel > > The RISC-V port requires that kernel PGD entries are to be > synchronized between MMs. This is done via the vmalloc_fault() > function, that simply copies the PGD entries from init_mm to the > faulting one. > > Historically, faulting in PGD entries have been a source for both bugs > [1], and poor performance. > > One way to get rid of vmalloc faults is by pre-allocating the PGD > entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on > SV39). The pre-allocation function is pulled from J=C3=B6rg R=C3=B6del's = x86 > work, with the addition of 3-level page tables (PMD allocations). > > The pmd_alloc() function needs the ptlock cache to be initialized > (when split page locks is enabled), so the pre-allocation is done in a > RISC-V specific pgtable_cache_init() implementation. > > Pre-allocate the kernel PGD entries for the vmalloc/modules area, but > only for 64b platforms. > > Link: https://lore.kernel.org/lkml/20200508144043.13893-1-joro@8bytes.org= / # [1] > Signed-off-by: Bj=C3=B6rn T=C3=B6pel ...and the build was bitten by nommu [1]. I'll hold off the v2 a bit, to see if there's any other comments. Bj=C3=B6rn [1] https://patchwork.kernel.org/project/linux-riscv/patch/20230529180023.2= 89904-1-bjorn@kernel.org/