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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 30149C38142 for ; Thu, 19 Jan 2023 04:49:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229973AbjASEtg (ORCPT ); Wed, 18 Jan 2023 23:49:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229831AbjASEsb (ORCPT ); Wed, 18 Jan 2023 23:48:31 -0500 Received: from mail-pj1-f44.google.com (mail-pj1-f44.google.com [209.85.216.44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1125E78578; Wed, 18 Jan 2023 20:43:39 -0800 (PST) Received: by mail-pj1-f44.google.com with SMTP id a14-20020a17090a70ce00b00229a2f73c56so4679343pjm.3; Wed, 18 Jan 2023 20:43:39 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=0d4sY4KYUa7j537BEEIS3yVmB57Y9RzPLByhF0pYcg0=; b=p1u9uQAtSu11kyaQ7NN86iY92w1WAoNEPWqTeMMo0ZT9OMydhNSP1zawCZdQe31/m/ CwZIQ+5Tya4Txs8IR3Wjn0pU/CQvwziC/EYZbVCmFZMq5uSSNg2UBtgweeZ+IsqOhqcc YaEpaEBzcsFaMr+AmDwYD8ebv3bMywThknoTSr0xzhVZLvRe5JkVpTiZNwqLpfv3geHl fFuV1GJsJt8halKm6aY8oo7IiXPrkM6bf5jVP6F8dgq/pLGML2MmQ52oXk7aFFwfoafa uOeWxOu6XQYz6Uc01aTrNCtqTIFQxpEcpFD8iofqWknT+JXwQgoavudgMQf+jG//qHxI 8sag== X-Gm-Message-State: AFqh2kqZEbr8ANLb8gwcXU+LVdXAqNIQR4kXKpye4hPbZELUQTpHyCje hzssSYhY07hAPdMff1LT/6g= X-Google-Smtp-Source: AMrXdXsA+sH1dun7aToK6KPMwZLBrSu2P+Ad0hT+aymj16K/rYS4kTMxv9n52wqM9jKUZGY5rYEtKw== X-Received: by 2002:a17:902:ebc9:b0:194:85da:16 with SMTP id p9-20020a170902ebc900b0019485da0016mr10777949plg.13.1674103393875; Wed, 18 Jan 2023 20:43:13 -0800 (PST) Received: from [192.168.51.14] ([98.51.102.78]) by smtp.gmail.com with ESMTPSA id j15-20020a170903028f00b00190c6518e30sm24032502plr.243.2023.01.18.20.43.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Jan 2023 20:43:13 -0800 (PST) Message-ID: <0e120274-29d8-cb53-2190-d82eabf4c431@acm.org> Date: Wed, 18 Jan 2023 20:43:10 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v3 0/9] Add support for segments smaller than one page Content-Language: en-US To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, Jaegeuk Kim , Avri Altman , Adrian Hunter , Christoph Hellwig , Ming Lei References: <20230118225447.2809787-1-bvanassche@acm.org> <52073ee8-72ab-f424-1738-c56bc8d5cd67@kernel.dk> From: Bart Van Assche In-Reply-To: <52073ee8-72ab-f424-1738-c56bc8d5cd67@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 1/18/23 17:18, Jens Axboe wrote: > On 1/18/23 3:54?PM, Bart Van Assche wrote: >> Hi Jens, >> >> Several embedded storage controllers need support for DMA segments that are >> smaller than the size of one virtual memory page. Hence this patch series. >> Please consider this patch series for the next merge window. > > Before any real reviews are done, I have to ask "why?". This is pretty > hairy code in the middle of the fast path for some obscure controller. > Why would anyone ship that with > 4k page sizes rather than ship it with > a controller that is sane? Hi Jens, The new config variable CONFIG_BLK_SUB_PAGE_SEGMENTS has been introduced to make sure that the hot path is *not* affected if that config variable is disabled. Regarding the question "why": the Google Android team would like to improve performance by switching from 4 KiB pages to 16 KiB pages. One of the widely used UFS controllers (Exynos) has a maximum segment size of 4 KiB. Hence this patch series. This patch series is not only useful for phones but also for Tesla cars since Tesla cars use an Exynos UFS controller. A contributor to the MMC driver told me that this patch series would allow to simplify the MMC driver significantly (I have not yet double checked this). Bart.