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 7521EC43142 for ; Fri, 3 Aug 2018 02:52:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FCD521724 for ; Fri, 3 Aug 2018 02:52:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="iVbyf//q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2FCD521724 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 S1727163AbeHCEqj (ORCPT ); Fri, 3 Aug 2018 00:46:39 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:35996 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725736AbeHCEqj (ORCPT ); Fri, 3 Aug 2018 00:46:39 -0400 Received: by mail-pf1-f195.google.com with SMTP id b11-v6so2427329pfo.3; Thu, 02 Aug 2018 19:52:35 -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=+rx5nRSqIHZl4QDpTMaJBkINy5D1R74Z8iUnocz+tuA=; b=iVbyf//q9sI5DmxRy9BH4n0w3dRhhrEWfOIXI0s0v1XG28yTd+vcS69cmo61D01DP1 cHvwSQdHnzgUYO7PKfQtDd3J7cmwbqMbd+/ApTJFokuDkcsgdSBLgaGDXShS7aHHNjLH 6ncNMCXF/T5GGajAJLaBqfXnQeSLGS+sBhqff23Kq+9PPcbvF62/dPMOdNnhUCM3nyjs dpn/bNtCcpSKbayzmgNmvVRugO/BcC2vhrP3OgQNGwI2nhufyLOHJdrsif458PcHghVe KDDSOzLpSkMWftEVWG0kxiPt9oVdgxV5SmFTNXd28B8vuMwLP5T6AaITAmLvQ7DnGZSD uGQw== 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=+rx5nRSqIHZl4QDpTMaJBkINy5D1R74Z8iUnocz+tuA=; b=NF7VxTwTkwMFHx3hCju+p6akY3CfwOG9KeZtCevJGqDg24vl1B0PGr6OHjPCoZspLD xK+mIaCDNnxvds6RttaDCTQHeolDdrozbKOYb+S1V5BwZ0FnHannBhg3gJJlsp0ZUpLx 65I5O6gdeP+VmjUFTnIeZqedly8P0jJ3j1bq9E1oi16ZsydS8gjEa9nKcY05OclKCWmG KGA3dGchFdoTiCG9XZ7ICOpNcmTI7FZ6jThtrL4G4Qzt0M9Mckz73I5dSRJFTF9RgV0T VJnMy5zFlabR2PVDMoZuby/XzMKa20MhSMgOzUORzTTwlA3BakCDDPENHrh5zUd/BC9Y Ygpw== X-Gm-Message-State: AOUpUlGoFoV1O72rEjRAC2anv8bwtxMdFiOxlCCp2QH9Jlx8qMpp7nKq XscH9zMwPg3u4JoXTEbH6j4K4zr7 X-Google-Smtp-Source: AAOMgpc1bnDW1r4L/ePhdoINQhfU+6B2nk7rBL7fQFPeY7EAGj3wxN4TjWq/dBJsv2AEJe3wnsPVig== X-Received: by 2002:a63:5025:: with SMTP id e37-v6mr1868289pgb.341.1533264754811; Thu, 02 Aug 2018 19:52:34 -0700 (PDT) Received: from localhost ([175.223.10.158]) by smtp.gmail.com with ESMTPSA id z184-v6sm4001056pgd.83.2018.08.02.19.52.32 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 02 Aug 2018 19:52:33 -0700 (PDT) Date: Fri, 3 Aug 2018 11:52:30 +0900 From: Sergey Senozhatsky To: Sergey Senozhatsky Cc: Andrew Morton , Minchan Kim , LKML , Tino Lehnig , stable@vger.kernel.org, Jens Axboe Subject: Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback feature Message-ID: <20180803025230.GA502@jagdpanzerIV> References: <20180802051112.86174-1-minchan@kernel.org> <20180802141304.d0589ddc5f8213429ab3b565@linux-foundation.org> <20180803023929.GA7500@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180803023929.GA7500@jagdpanzerIV> 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 (08/03/18 11:39), Sergey Senozhatsky wrote: > [..] > > > 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 ^ASYNC IO -ss