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 X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7564FC43142 for ; Fri, 3 Aug 2018 02:36:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2AEBF21717 for ; Fri, 3 Aug 2018 02:36:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="L2qAi5ZZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2AEBF21717 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727091AbeHCEaP (ORCPT ); Fri, 3 Aug 2018 00:30:15 -0400 Received: from mail-pl0-f67.google.com ([209.85.160.67]:45810 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726190AbeHCEaP (ORCPT ); Fri, 3 Aug 2018 00:30:15 -0400 Received: by mail-pl0-f67.google.com with SMTP id j8-v6so1868381pll.12; Thu, 02 Aug 2018 19:36:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=AX6xF/Zd/rGkWz2OM2zPw+EDntBi/qcRCOYadaNZHqg=; b=L2qAi5ZZ0F35ObO1RCkYUfoUMc9f0jovInAqM76ou2W9W/CaGtoB+jOAvj8KWHMZRk XO6f//vh84yd3XKfUioRzwNEMBDMsf2IR+lGD7iOjWvfPR/u7WGu5Nhfk0STZNGcA7qO 2PiK3Yg7aPUpa0QMZsc6jn3xPoQOSK0feFljApBNEGKEW58TYSUU/DxbFsIK8oKq8aUJ MhBxCSIof+UHU+jWPcR6jopALlTnpimvHB6BEIJXcnWxFivZ83ci+pyjgMUqyh6cjB2a gT2opiCIF30ydalT1R545TweyLnSDMSjnmAhRdBKZ92nsUn3M+aMDQxfhpPD9A+5si0l qYgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=AX6xF/Zd/rGkWz2OM2zPw+EDntBi/qcRCOYadaNZHqg=; b=d7xabo5U/UuGf8BTvwkb4qvvrIDfZXwC/6omiQ5i3XfsR1REID6icrxvEh6vtRbysk bNd+yRJ+QYGAd2E1besIYoU/ahsZItKGk2AIXl+yKFhv6q+gWUQEMZ0gISyt3yCpAwQL aDK34bMo47rCxTmNK1xkJdPcOKHaDaivBRrWWwA+5dLMVkQsC8FKz0HpfX5/t06yVt1U GBXP2i9yPm8U0RfUldXTXSZZHlkfNycivNXoUWXuyEPaycTibcVAgQwg7WAxQ/Uc2tyK eYtYEha71b/l8fIQ4Q4lz/6pxoT6g1eENnfSjd2WpNDXwxYCTDSTcR3wra0eGHppkDjp Ggdg== X-Gm-Message-State: AOUpUlFT4Uc3CXq1xuiLtdsZ7OFCgyWJpi+JaHlQixlRbIW6FshQ6cDL AG/dENXftoygT9yfGkz0B9w= X-Google-Smtp-Source: AAOMgpelfspZN15wqcEoquRs+h/KROMof+DTcXgB7F6eaohyOMrneOW7IZ9QwPjVg3ebJs+QQh88rw== X-Received: by 2002:a17:902:8c84:: with SMTP id t4-v6mr1815445plo.100.1533263773987; Thu, 02 Aug 2018 19:36:13 -0700 (PDT) Received: from localhost ([175.223.10.158]) by smtp.gmail.com with ESMTPSA id 1-v6sm5835739pfm.145.2018.08.02.19.36.12 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 02 Aug 2018 19:36:12 -0700 (PDT) Date: Fri, 3 Aug 2018 11:39:29 +0900 From: Sergey Senozhatsky To: Andrew Morton Cc: Minchan Kim , LKML , Sergey Senozhatsky , Tino Lehnig , stable@vger.kernel.org, Jens Axboe Subject: Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback feature Message-ID: <20180803023929.GA7500@jagdpanzerIV> References: <20180802051112.86174-1-minchan@kernel.org> <20180802141304.d0589ddc5f8213429ab3b565@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180802141304.d0589ddc5f8213429ab3b565@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (08/02/18 14:13), Andrew Morton wrote: [..] > That changelog is rather hard to follow. Please review my edits: > > : If zram supports writeback feature, it's no longer a BD_CAP_SYNCHRONOUS_IO ^BDI_CAP_SYNCHRONOUS_IO [..] > A reader looking at this would wonder "why the heck are we doing that". > Adding a code comment would help them. The interesting thing here is that include/linux/backing-dev.h BDI_CAP_SYNCHRONOUS_IO comment says "Device is so fast that asynchronous IO would be inefficient." Which is not the reason why BDI_CAP_SYNCHRONOUS_IO is used by ZRAM. Probably, the comment needs to be updated as well. Both SWP_SYNCHRONOUS_IO and BDI_CAP_SYNCHRONOUS_IO tend to pivot "efficiency" [looking at the comments], but in ZRAM's case the whole reason to use SYNC IO is a race condition and user-after-free that follows. -ss