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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BD30C433F5 for ; Mon, 31 Jan 2022 04:55:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B94E66B007B; Sun, 30 Jan 2022 23:55:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B43D66B007D; Sun, 30 Jan 2022 23:55:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A0C436B007E; Sun, 30 Jan 2022 23:55:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0118.hostedemail.com [216.40.44.118]) by kanga.kvack.org (Postfix) with ESMTP id 947866B007B for ; Sun, 30 Jan 2022 23:55:31 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 4EE5D987BE for ; Mon, 31 Jan 2022 04:55:31 +0000 (UTC) X-FDA: 79089368862.07.56CA6F6 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf08.hostedemail.com (Postfix) with ESMTP id 9AE3C160002 for ; Mon, 31 Jan 2022 04:55:30 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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 53109210F8; Mon, 31 Jan 2022 04:55:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1643604929; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NdB1XHgAD5AGIVVsRx2EQeO3d7TEVq5YDPKnGsmvoSo=; b=ftP6guEKgOcD+qcuWJB4Xv35Y3zrOaBJa7dEeRwiPxi7j0RdkmePW0y4SVOUF1tfiQx3Am M2ehez+KMUHgYKFc9mWEZyGEQxHrMSe3AHK/zkmITG8sjFg11LH/NEKTuy40HetAAAONEF eXNds0UoJYZ71pbvTaaTrdKyjuFva8Y= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1643604929; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NdB1XHgAD5AGIVVsRx2EQeO3d7TEVq5YDPKnGsmvoSo=; b=8N8jRXLY8+y2eslTTS+XbYtUzAQY0tbcbK/gwomrzZVkGqleGjjbAcNdu1NK2vBOJTdXB7 h3qF/JOYSUqsinBg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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 imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C7AA113638; Mon, 31 Jan 2022 04:55:25 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id kCDWIL1r92H1FgAAMHmgww (envelope-from ); Mon, 31 Jan 2022 04:55:25 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit MIME-Version: 1.0 From: "NeilBrown" To: "Matthew Wilcox" Cc: "Andrew Morton" , "Jeff Layton" , "Ilya Dryomov" , "Miklos Szeredi" , "Trond Myklebust" , "Anna Schumaker" , linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] nfs: remove reliance on bdi congestion In-reply-to: References: <164360127045.4233.2606812444285122570.stgit@noble.brown>, <164360183350.4233.691070075155620959.stgit@noble.brown>, Date: Mon, 31 Jan 2022 15:55:22 +1100 Message-id: <164360492268.18996.14760090171177015570@noble.neil.brown.name> X-Rspam-User: nil X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9AE3C160002 X-Stat-Signature: 6ybzg9k7qzpnmmeb8bx4cei36s3qn6cq Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=ftP6guEK; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=8N8jRXLY; dmarc=pass (policy=none) header.from=suse.de; spf=pass (imf08.hostedemail.com: domain of neilb@suse.de designates 195.135.220.28 as permitted sender) smtp.mailfrom=neilb@suse.de X-HE-Tag: 1643604930-732754 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, 31 Jan 2022, Matthew Wilcox wrote: > On Mon, Jan 31, 2022 at 03:03:53PM +1100, NeilBrown wrote: > > - .writepage to return AOP_WRITEPAGE_ACTIVATE if WB_SYNC_NONE > > and the flag is set. > > Is this actually useful? I ask because Dave Chinner believes > the call to ->writepage in vmscan to be essentially unused. He would be wrong ... unless "essentially" means "mostly" rather than "totally". swap-out to NFS results in that ->writepage call. Of course swap_writepage ignores sync_mode, so this might not be entirely relevant. But the main point of the patch is not to return AOP_WRITEPAGE_ACTIVATE to vmscan. It is to avoid writing at all when WB_SYNC_NONE and congested. e.g. for POSIX_FADV_DONTNEED It is also to allow the removal of congestion tracking with minimal changes to behaviour. If I end up changing some dead code into different dead code, I really don't care. I'm not here to clean up all dead code - only the dead code specifically related to congestion. NeilBrown > See commit 21b4ee7029c9, and I had a followup discussion with him > on IRC: > > dchinner: did you gather any stats on how often ->writepage was > being called by pageout() before "xfs: drop ->writepage completely" > was added? > willy: Never saw it on XFS in 3 years in my test environment... > I don't ever recall seeing the memory reclaim guards we put on > ->writepage in XFS ever firing - IIRC they'd been there for the best > part of a decade. > not so much the WARN_ON firing but the case where it actually calls > iomap_writepage > willy: I mean both - I was running with a local patch that warned > on writepage for a long time, regardless of where it was called from. > > I can believe things are different for a network filesystem, or maybe > XFS does background writeback better than other filesystems, but it > would be intriguing to be able to get rid of ->writepage altogether > (or at least from pageout(); migrate.c may be a thornier proposition). > >