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[60.241.56.246]) by smtp.gmail.com with ESMTPSA id p68sm4145337pfb.80.2019.06.10.07.47.14 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 10 Jun 2019 07:47:15 -0700 (PDT) Date: Tue, 11 Jun 2019 00:44:49 +1000 From: Nicholas Piggin Subject: Re: [PATCH 4/4] mm/vmalloc: Hugepage vmalloc mappings To: Mark Rutland References: <20190610043838.27916-1-npiggin@gmail.com> <20190610043838.27916-4-npiggin@gmail.com> <20190610141036.GA16989@lakrids.cambridge.arm.com> In-Reply-To: <20190610141036.GA16989@lakrids.cambridge.arm.com> MIME-Version: 1.0 User-Agent: astroid/0.14.0 (https://github.com/astroidmail/astroid) Message-Id: <1560177786.t6c5cn5hw4.astroid@bobo.none> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Mark Rutland's on June 11, 2019 12:10 am: > Hi, >=20 > On Mon, Jun 10, 2019 at 02:38:38PM +1000, Nicholas Piggin wrote: >> For platforms that define HAVE_ARCH_HUGE_VMAP, have vmap allow vmalloc t= o >> allocate huge pages and map them >>=20 >> This brings dTLB misses for linux kernel tree `git diff` from 45,000 to >> 8,000 on a Kaby Lake KVM guest with 8MB dentry hash and mitigations=3Dof= f >> (performance is in the noise, under 1% difference, page tables are likel= y >> to be well cached for this workload). Similar numbers are seen on POWER9= . >=20 > Do you happen to know which vmalloc mappings these get used for in the > above case? Where do we see vmalloc mappings that large? Large module vmalloc could be subject to huge mappings. > I'm worried as to how this would interact with the set_memory_*() > functions, as on arm64 those can only operate on page-granular mappings. > Those may need fixing up to handle huge mappings; certainly if the above > is all for modules. Good point, that looks like it would break on arm64 at least. I'll work on it. We may have to make this opt in beyond HUGE_VMAP. Thanks, Nick =