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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 F25D3C07E95 for ; Wed, 7 Jul 2021 11:03:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D457D61C7F for ; Wed, 7 Jul 2021 11:03:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231360AbhGGLGP (ORCPT ); Wed, 7 Jul 2021 07:06:15 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:54432 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230354AbhGGLGP (ORCPT ); Wed, 7 Jul 2021 07:06:15 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 3A624220A9; Wed, 7 Jul 2021 11:03:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1625655814; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BgwYsC6ZoaxZL4BZ5yOzWNI4AOSUP3oyE9DclzfFN0E=; b=s7GlYmyY7GpGckJrnHxNjzV/1A82IqWHbFQpY3fRU3TsVv8kYjD7Uvv7f9KtjjtCgm9bvl MODop/1i+cwvBLzxZecn/nb4MBd2Z1lchOjj+0lhS19tC7tLXOyil5c2SEYozn5Ndn47gK GZTiW2bWuCkhiefTMzHEObOoFaRE//s= Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id E7F4E13998; Wed, 7 Jul 2021 11:03:33 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id ogBCNQWK5WDYXgAAGKfGzw (envelope-from ); Wed, 07 Jul 2021 11:03:33 +0000 Subject: Re: [PATCH v2 5/8] fs: add a filemap_fdatawrite_wbc helper To: Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com, linux-fsdevel@vger.kernel.org References: From: Nikolay Borisov Message-ID: <5425d3ef-ef71-626b-17f9-b6b5bac27815@suse.com> Date: Wed, 7 Jul 2021 14:03:33 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 29.06.21 г. 16:59, Josef Bacik wrote: > Btrfs sometimes needs to flush dirty pages on a bunch of dirty inodes in > order to reclaim metadata reservations. Unfortunately most helpers in > this area are too smart for us > > 1) The normal filemap_fdata* helpers only take range and sync modes, and > don't give any indication of how much was written, so we can only > flush full inodes, which isn't what we want in most cases. > 2) The normal writeback path requires us to have the s_umount sem held, > but we can't unconditionally take it in this path because we could > deadlock. > 3) The normal writeback path also skips inodes with I_SYNC set if we > write with WB_SYNC_NONE. This isn't the behavior we want under heavy > ENOSPC pressure, we want to actually make sure the pages are under > writeback before returning, and if another thread is in the middle of > writing the file we may return before they're under writeback and > miss our ordered extents and not properly wait for completion. > 4) sync_inode() uses the normal writeback path and has the same problem > as #3. > > What we really want is to call do_writepages() with our wbc. This way > we can make sure that writeback is actually started on the pages, and we > can control how many pages are written as a whole as we write many > inodes using the same wbc. Accomplish this with a new helper that does > just that so we can use it for our ENOSPC flushing infrastructure. > > Signed-off-by: Josef Bacik Reviewed-by: Nikolay Borisov