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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 E5193C433DB for ; Tue, 23 Mar 2021 15:42:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 71258619BD for ; Tue, 23 Mar 2021 15:42:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 71258619BD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C66C56B020B; Tue, 23 Mar 2021 11:42:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BEFDA6B0246; Tue, 23 Mar 2021 11:42:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A68B86B0249; Tue, 23 Mar 2021 11:42:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0205.hostedemail.com [216.40.44.205]) by kanga.kvack.org (Postfix) with ESMTP id 8B77A6B020B for ; Tue, 23 Mar 2021 11:42:28 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 533CA8249980 for ; Tue, 23 Mar 2021 15:42:28 +0000 (UTC) X-FDA: 77951555976.19.E5CEBE4 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf17.hostedemail.com (Postfix) with ESMTP id 4930F407F8FE for ; Tue, 23 Mar 2021 15:42:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=m59UZWXfLRd0rO3ZUPVC1bRgtsSO+J63cyZVGfi/nRE=; b=amH4eqTwef6dVrvHenjYMF2QHe VBb9Q2JjD7+u3m0l1l4SKU/xLU1xjk3kmO/2yva7BgvxS69jjx2AZUNxUFEjkh/Qi6pe1J1nGiSvl EfyjTb0RpmLROj5wb6ij8NoVPFu0El5Fyy0g2RuiipkXZg1xfYEErUtkQE/miIfMPBLIDr5CwXa5l 10RQSBb587QnmctXWSAZdvIDpcdd6eE6oGFMB/lOsAoTkRINXxOjti1r88wXh//AgeitaJZFpof4O 8TI0VDCxuR8Hi+0WM0LHQYcWp4LAI7kx8LEp4/0mf8BNYWfKWmh4SMebMhGVqNDLZd3euxsowQMnp Wo0GLxzw==; Received: from hch by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lOj9p-00AEQz-29; Tue, 23 Mar 2021 15:41:34 +0000 Date: Tue, 23 Mar 2021 15:41:25 +0000 From: Christoph Hellwig To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: set_page_dirty variants Message-ID: <20210323154125.GA2438080@infradead.org> References: <20210322011907.GB1719932@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210322011907.GB1719932@casper.infradead.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4930F407F8FE X-Stat-Signature: tbcqi75zoobterehihnu34z9w8shgj1y Received-SPF: none (casper.srs.infradead.org>: No applicable sender policy available) receiver=imf17; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616514146-876214 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Mar 22, 2021 at 01:19:07AM +0000, Matthew Wilcox wrote: > I'd like to get it down to zero. After all, the !mapping case in > set_page_dirty() is exactly what we want. So is there a problem > with doing this? > > +++ b/mm/page-writeback.c > @@ -2562 +2562 @@ int set_page_dirty(struct page *page) > - if (likely(mapping)) { > + if (likely(mapping && mapping_can_writeback(mapping))) { > > But then I noticed that we have both mapping_can_writeback() > and mapping_use_writeback_tags(), and I'm no longer sure > which one to use. Also, why don't we mirror the results of > inode_to_bdi(mapping->host)->capabilities & BDI_CAP_WRITEBACK into > a mapping->flags & AS_something bit? Probably because no one has bothered to submit a patch yet.