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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1E39C433EF for ; Tue, 19 Oct 2021 22:00:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 230CC6128B for ; Tue, 19 Oct 2021 22:00:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 230CC6128B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 7D5D76B006C; Tue, 19 Oct 2021 18:00:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 78450900002; Tue, 19 Oct 2021 18:00:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6253E6B0072; Tue, 19 Oct 2021 18:00:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 510E66B006C for ; Tue, 19 Oct 2021 18:00:29 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 0D96C181AEF15 for ; Tue, 19 Oct 2021 22:00:29 +0000 (UTC) X-FDA: 78714556578.15.0450EF4 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf26.hostedemail.com (Postfix) with ESMTP id 9494620019ED for ; Tue, 19 Oct 2021 22:00:29 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 3FE0960FDA; Tue, 19 Oct 2021 22:00:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1634680827; bh=Rk43kt/rzfIF9w6y1lPOwDQjIprPyWMfV86zk0IuZz4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=mM0x0H7FCOinXZ4mdFMqWNW7smp4C8w8lQtnMlj9VvCKdIW/SFcPU/RxPsKDbsP1t z5A59chQaUCEMvnwBQDimhND52a8u62ysdVmWCy88aEidcmxII8iqtpdqeGNfRkfsx waP9eBwf4tcdC+5UkRoYp/O1Jy625nCCmK4DZTDE= Date: Tue, 19 Oct 2021 15:00:25 -0700 From: Andrew Morton To: Mel Gorman Cc: NeilBrown , "Theodore Ts'o" , Andreas Dilger , "Darrick J . Wong" , Matthew Wilcox , Michal Hocko , Dave Chinner , Rik van Riel , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Linux-MM , Linux-fsdevel , LKML Subject: Re: [PATCH v4 0/8] Remove dependency on congestion_wait in mm/ Message-Id: <20211019150025.c62a0c72538d1f9fa20f1e81@linux-foundation.org> In-Reply-To: <20211019090108.25501-1-mgorman@techsingularity.net> References: <20211019090108.25501-1-mgorman@techsingularity.net> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9494620019ED X-Stat-Signature: 93y1eyo6x9z6zxkp7r1jw4nsmhkeozf3 Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=mM0x0H7F; spf=pass (imf26.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-HE-Tag: 1634680829-50175 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 Tue, 19 Oct 2021 10:01:00 +0100 Mel Gorman wrote: > Changelog since v3 > o Count writeback completions for NR_THROTTLED_WRITTEN only > o Use IRQ-safe inc_node_page_state > o Remove redundant throttling > > This series is also available at > > git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-reclaimcongest-v4r2 > > This series that removes all calls to congestion_wait > in mm/ and deletes wait_iff_congested. It's not a clever > implementation but congestion_wait has been broken for a long time > (https://lore.kernel.org/linux-mm/45d8b7a6-8548-65f5-cccf-9f451d4ae3d4@kernel.dk/). The block layer doesn't call clear_bdi_congested() at all. I never knew this until recent discussions :( So this means that congestion_wait() will always time out, yes? > Even if congestion throttling worked, it was never a great idea. Well. It was a good idea until things like isolation got added! > While > excessive dirty/writeback pages at the tail of the LRU is one possibility > that reclaim may be slow, there is also the problem of too many pages > being isolated and reclaim failing for other reasons (elevated references, > too many pages isolated, excessive LRU contention etc). > > This series replaces the "congestion" throttling with 3 different types. > > o If there are too many dirty/writeback pages, sleep until a timeout > or enough pages get cleaned > o If too many pages are isolated, sleep until enough isolated pages > are either reclaimed or put back on the LRU > o If no progress is being made, direct reclaim tasks sleep until > another task makes progress with acceptable efficiency. > > This was initially tested with a mix of workloads that used to trigger > corner cases that no longer work. Mix of workloads is nice, but a mix of devices is more important here. I trust some testing was done on plain old spinning disks? And USB storage, please! And NFS plays with BDI congestion. Ceph and FUSE also. We've had complaints about this stuff forever. Usually of the form of interactive tasks getting horridly stalled by writeout/swap activity.