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d=linux-foundation.org; s=korg; t=1690397567; bh=CxP8YWy391Ug3Hzfo8N8jl+lKHtBCe6vTm0NgR+xnP4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=RNkrFUcloKc5NnzwRJDVvUvhoj6yDvBiENSJ87Cd3Bd9toX/a3lkLBZS5VyQ+7voo PXSrdgkqwWLgN7+h5CX/VE3VmHAnEgNiDXyy+CErHGG6FK8L4UpqrLQ27ucpduXhko SYIhAcljZnlfkqoU2ALxBcg014/dUH2dx8cuggKg= Date: Wed, 26 Jul 2023 11:52:46 -0700 From: Andrew Morton To: Aneesh Kumar K V Cc: linux-mm@kvack.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, christophe.leroy@csgroup.eu, Oscar Salvador , Mike Kravetz , Dan Williams , Joao Martins , Catalin Marinas , Muchun Song , Will Deacon Subject: Re: [PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64 Message-Id: <20230726115246.b6ed2a08aa7b648671107a8a@linux-foundation.org> In-Reply-To: <47feb4fe-f461-a2c2-1368-5480d00d0f1d@linux.ibm.com> References: <20230724190759.483013-1-aneesh.kumar@linux.ibm.com> <20230725122959.e9b79e7528cd3084802fa6d0@linux-foundation.org> <47feb4fe-f461-a2c2-1368-5480d00d0f1d@linux.ibm.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 042E8C0010 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: sn6nmwo9di3psey7fb6ar69dwgb1775i X-HE-Tag: 1690397568-952419 X-HE-Meta: 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 zIRqwDqU n9Gbf/HQjL6Sm6fh/CayHptQhwzY1ixV9nPP/oFBS7hLObd4B0RxeodJ6yzlc7zE/wgam/wFH9/zXXFxTcbtCL/thC740crVCyDQ24BH86Q6g3NMKmcV332jGNjsHbixlbAQlUoVSgbWwoynHOgkeBoXBe9ElHKzN3sUcat+YS13La4U9EGOcco22e8I84TOoQ8qgWEEzunYtQVPqGauXl3hZaqbTT3K8u4S0VeGpvv5OXLzMnaNR0oNws1Po9eyXnaP4OBitWOmxm5dFnJ4e4A/GvIG/L+zmJNYVyqQILhf62SGmAenActQqblJXMDBY4gKwxTEXVyDHFVEuemFIEP5zNwB3DLh+6sp0 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 Wed, 26 Jul 2023 10:59:32 +0530 Aneesh Kumar K V wrote: > On 7/26/23 12:59 AM, Andrew Morton wrote: > > On Tue, 25 Jul 2023 00:37:46 +0530 "Aneesh Kumar K.V" wrote: > > > >> This patch series implements changes required to support DAX vmemmap > >> optimization for ppc64. > > > > Do we have any measurements to help us understand the magnitude > > of this optimization? > > > > And any documentation which helps users understand whether and > > why they should enable this feature? > > That is memory space optimization due to kernel reusing the tail page struct pages. The details > of the optimization is documented in patch 11. We document there the impact with both 4k and > 64K page size. I suppose that with sufficient arithmetic one could use Documentation/powerpc/vmemmap_dedup.rst to figure out the bottom-line savings. I was more expecting a straightforward statement in the [0/N] overview to help people understand why they're reading this patchset at all. Like "saves 5% of total memory on my XXX machine".