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[217.140.110.172]) by mx.google.com with ESMTP id b10si2433448ejh.360.2019.06.10.23.17.22 for ; Mon, 10 Jun 2019 23:17:23 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 04483344; Mon, 10 Jun 2019 23:17:22 -0700 (PDT) Received: from [10.162.43.135] (p8cg001049571a15.blr.arm.com [10.162.43.135]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 847F13F73C; Mon, 10 Jun 2019 23:17:20 -0700 (PDT) Subject: Re: [PATCH 4/4] mm/vmalloc: Hugepage vmalloc mappings To: Nicholas Piggin , Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org References: <20190610043838.27916-1-npiggin@gmail.com> <20190610043838.27916-4-npiggin@gmail.com> <20190610141036.GA16989@lakrids.cambridge.arm.com> <1560177786.t6c5cn5hw4.astroid@bobo.none> From: Anshuman Khandual Message-ID: Date: Tue, 11 Jun 2019 11:47:39 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1560177786.t6c5cn5hw4.astroid@bobo.none> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 06/10/2019 08:14 PM, Nicholas Piggin wrote: > Mark Rutland's on June 11, 2019 12:10 am: >> Hi, >> >> 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 to >>> allocate huge pages and map them >>> >>> 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=off >>> (performance is in the noise, under 1% difference, page tables are likely >>> to be well cached for this workload). Similar numbers are seen on POWER9. >> >> 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. This is another reason we might need to have an arch opt-ins like the one I mentioned before.