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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 54759C4361B for ; Tue, 8 Dec 2020 06:12:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 08A4623A57 for ; Tue, 8 Dec 2020 06:12:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726667AbgLHGMG (ORCPT ); Tue, 8 Dec 2020 01:12:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:44364 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725979AbgLHGMF (ORCPT ); Tue, 8 Dec 2020 01:12:05 -0500 Date: Mon, 7 Dec 2020 22:11:23 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607407885; bh=6eVsoX1UfUHRal2QvrfoS2AS5yZMliy97WzwbEbV8Lw=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=b5+clt9E+XWruWrulzy8brKCYKPtc+U0zAbBxonMi99vz0vq2qL1HNoQbZX4nst4a 6wdYBbQcebmWtEB6MBWfv/tfdSJSpTRzrGwdJWtjiEQ/LrThHH8Fwr7lBSnmDFhel+ g2iNerWRtHpiiQ2ncO9s+2xhrElmDaqxYlwIw/gJgsq8XF52qDQjQyLlOUcgPTTKPI /IFeIn/pxcsXbDpmL/1/U+NmqYEbgOqK6KwKowSHJ2qD8yVu1K2dF3V7txI7yoMjj7 XD/B3gJkbWt0Po8I1aps1bw9pBqmUN1y+VOi3diqNJYT2h1gzY9aBxMQglpYgBYSrd pvYgyOs+ewE8Q== From: Eric Biggers To: Daeho Jeong Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Jaegeuk Kim , Daeho Jeong Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in decompression Message-ID: References: <20201205042626.1113600-1-daeho43@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 08, 2020 at 08:51:45AM +0900, Daeho Jeong wrote: > > I am trying to review this but it is very hard, as the f2fs compression code is > > very hard to understand. > > > > It looks like a 'struct decompress_io_ctx' represents the work to decompress a > > particular cluster. Since the compressed data of the cluster can be read using > > multiple bios, there is a reference count of how many pages are remaining to be > > read before all the cluster's pages have been read and decompression can start. > > > > What I don't understand is why that reference counting needs to work differently > > depending on whether verity is enabled or not. Shouldn't it be exactly the > > same? > > > > There also seems to be some confusion about the scope of STEP_VERITY. Before > > f2fs compression was added, it was a per-bio thing. But now in a compressed > > file, it's really a per-cluster thing, since all decompressed pages in a > > compressed cluster are verified (or not verified) at once. > > > > Wouldn't it make a lot more sense to, when a cluster needs both compression and > > verity, *not* set STEP_VERITY on the bios, but rather set a similar flag in the > > decompress_io_ctx? > > > > Eric, > > Decompression and verity can be executed in different thread contexts > in different timing, so we need separate counts for each. > > We already use STEP_VERITY for non-compression case, so I think using > this flag in here looks more making sense. > > Thanks, That didn't really answer my questions. I gave up trying to review this patch as the compression post-read handling is just way too weird and hard to understand. I wrote a patch to clean it all up instead, please take a look: https://lkml.kernel.org/r/20201208060328.2237091-1-ebiggers@kernel.org - Eric