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[209.85.220.65]) by mx.google.com with SMTPS id n11sor10685185plg.60.2019.03.25.09.59.33 for (Google Transport Security); Mon, 25 Mar 2019 09:59:33 -0700 (PDT) Received-SPF: pass (google.com: domain of salyzyn@android.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@android.com header.s=20161025 header.b=vqXpLsAU; spf=pass (google.com: domain of salyzyn@android.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=salyzyn@android.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=android.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=android.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=NWGLIQGu38/jJb6e8uWtmgESprJGVMgumpIJ57GgwLQ=; b=vqXpLsAUGm0QT70kX4qwhbmciXz3cS7QYuXaQZf1e26ddA9ixDkoyH1skKslX3iVK9 U+yWZOWSgHV8bhdUFn28dzhI/SwxuP/uPdlwilQ8Zwe4VEmI0WKVyP9IAhi8pyL04eTI bTJXctHM6c0Kf0OAEgUhwGhw9urE1YlnLPivsY8jyT0xz0LWVR1FrqmKWJdNuavaFM/7 u/IQl743Qcbo6PgvrV7mgBYltaw80uUEbBty85iiwU0UL5oyh2cl6M7+Lx8F3nAPbBRP fO3QZ1DMn+N9myfUKaXFcCqzdlt0Xx7FTgpWGy7xyJ+eLzsmAESdOMRH2cttOuq0QPXZ wSZg== X-Google-Smtp-Source: APXvYqwXslOnXOKe7wC30klcY2KN8K5xcX4jq5xguuZL/3Igbc5bGQNlXFr+P0grfxvTw8OCG3cGEA== X-Received: by 2002:a17:902:e684:: with SMTP id cn4mr3383014plb.71.1553533172882; Mon, 25 Mar 2019 09:59:32 -0700 (PDT) Received: from nebulus.mtv.corp.google.com ([2620:0:1000:1612:b4fb:6752:f21f:3502]) by smtp.googlemail.com with ESMTPSA id z77sm30426023pfi.155.2019.03.25.09.59.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Mar 2019 09:59:32 -0700 (PDT) Subject: Re: [RFC PATCH] mm: readahead: add readahead_shift into backing device To: Fengguang Wu , Martin Liu Cc: akpm@linux-foundation.org, axboe@kernel.dk, dchinner@redhat.com, jenhaochen@google.com, salyzyn@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org References: <20190322154610.164564-1-liumartin@google.com> <20190325121628.zxlogz52go6k36on@wfg-t540p.sh.intel.com> From: Mark Salyzyn Message-ID: <9b194e61-f2d0-82cb-30ac-95afb493b894@android.com> Date: Mon, 25 Mar 2019 09:59:31 -0700 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: <20190325121628.zxlogz52go6k36on@wfg-t540p.sh.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB 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 03/25/2019 05:16 AM, Fengguang Wu wrote: > Martin, > > On Fri, Mar 22, 2019 at 11:46:11PM +0800, Martin Liu wrote: >> As the discussion https://lore.kernel.org/patchwork/patch/334982/ >> We know an open file's ra_pages might run out of sync from >> bdi.ra_pages since sequential, random or error read. Current design >> is we have to ask users to reopen the file or use fdavise system >> call to get it sync. However, we might have some cases to change >> system wide file ra_pages to enhance system performance such as >> enhance the boot time by increasing the ra_pages or decrease it to > > Do you have examples that some distro making use of larger ra_pages > for boot time optimization? Android (if you are willing to squint and look at android-common AOSP kernels as a Distro). > > Suppose N read streams with equal read speed. The thrash-free memory > requirement would be (N * 2 * ra_pages). > > If N=1000 and ra_pages=1MB, it'd require 2GB memory. Which looks > affordable in mainstream servers. That is 50% of the memory on a high end Android device ... > > Sorry but it sounds like introducing an unnecessarily twisted new > interface. I'm afraid it fixes the pain for 0.001% users while > bringing more puzzle to the majority others. >2B Android devices on the planet is 0.001%? I am not defending the proposed interface though, if there is something better that can be used, then looking into: > > Then let fadvise() and shrink_readahead_size_eio() adjust that > per-file ra_pages_shift. Sounds like this would require a lot from init to globally audit and reduce the read-ahead for all open files? Sincerely -- Mark Salyzyn