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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id 7si36540581pga.439.2019.08.02.01.12.24 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 02 Aug 2019 01:12:24 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of batv+e51aaead15bb68118d94+5822+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=J4P9XXFF; spf=pass (google.com: best guess record for domain of batv+e51aaead15bb68118d94+5822+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=BATV+e51aaead15bb68118d94+5822+infradead.org+hch@bombadil.srs.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=KjfLNU0SyqIyVrAxHzlRCdRO4H2dKobiLNT7ypOiSiU=; b=J4P9XXFF6r79xI9pt/gvdN9oA X2BwcCJGTOUfq1Js4lh22cDe6AkfCTnwQVmhlxluksQvNyI5oF9lpPy5MckRL2x9WShvEg2EGleyc pilujzQ40oIUsYl7Cd0HiAVfsD2LNRfimYy7A2AWWnE5cNuUYlfJoUISYSIQ7WGGauYbZ4KKLUOsw ZShxaJJyNljB1jTZLdCyTON4yE+V7sW94y0xtokoq4FUgM56q+Q4z5tYxT/ID2b1bjIQqDGRYUTtY rPEW3iODyLo8ESy8fFTBdNddfZI4K6k8qCDYVZSYYKnH3NAVbnCkynp0MrsiOL0OBLFFbBEf9Awve V3qlCc83g==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1htSfl-0004Xd-Uu; Fri, 02 Aug 2019 08:12:22 +0000 Date: Fri, 2 Aug 2019 01:12:21 -0700 From: Christoph Hellwig To: Dave Chinner Cc: Chris Mason , "linux-xfs@vger.kernel.org" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , Jens Axboe Subject: Re: [PATCH 09/24] xfs: don't allow log IO to be throttled Message-ID: <20190802081221.GA15849@infradead.org> References: <20190801021752.4986-1-david@fromorbit.com> <20190801021752.4986-10-david@fromorbit.com> <20190801235849.GO7777@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190801235849.GO7777@dread.disaster.area> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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 Fri, Aug 02, 2019 at 09:58:49AM +1000, Dave Chinner wrote: > Which simply reinforces the fact that that request type based > throttling is a fundamentally broken architecture. > > > It feels awkward to have one set of prio inversion workarounds for io.* > > and another for wbt. Jens, should we make an explicit one that doesn't > > rely on magic side effects, or just decide that metadata is meta enough > > to break all the rules? > > The problem isn't REQ_META blows throw the throttling, the problem > is that different REQ_META IOs have different priority. > > IOWs, the problem here is that we are trying to infer priority from > the request type rather than an actual priority assigned by the > submitter. There is no way direct IO has higher priority in a > filesystem than log IO tagged with REQ_META as direct IO can require > log IO to make progress. Priority is a policy determined by the > submitter, not the mechanism doing the throttling. > > Can we please move this all over to priorites based on > bio->b_ioprio? And then document how the range of priorities are > managed, such as: Yes, we need to fix the magic deducted throttling behavior, especiall the odd REQ_IDLE that in its various incarnations has been a massive source of toruble and confusion. Not sure tons of priorities are really helping, given that even hardware with priority level support usually just supports about two priorit levels.