From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 635BDC001DF for ; Wed, 26 Jul 2023 18:53:46 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=RNkrFUcl; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4RB32c5mmwz3cJH for ; Thu, 27 Jul 2023 04:53:44 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=RNkrFUcl; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux-foundation.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=akpm@linux-foundation.org; receiver=lists.ozlabs.org) Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4RB31c6Vsvz304b for ; Thu, 27 Jul 2023 04:52:51 +1000 (AEST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DC97761C63; Wed, 26 Jul 2023 18:52:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4FDFC433C7; Wed, 26 Jul 2023 18:52:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; 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 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-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: Will Deacon , Muchun Song , linux-mm@kvack.org, npiggin@gmail.com, Catalin Marinas , Dan Williams , Mike Kravetz , linuxppc-dev@lists.ozlabs.org, Joao Martins , Oscar Salvador Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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".