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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id r3si34590571plb.14.2019.08.02.11.34.22 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 02 Aug 2019 11:34:22 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@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=fGJG11C2; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@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=2kEy2KClG3alDj03YfM34b+mCKk6wTiisUQufFSVdlI=; b=fGJG11C2pbKbbrqF3XBVAwW6q KxNlRGiE/D5EhURS1DioBlHhyjyk1M8FPn06HpEbQdOWUPT4Gs+mlHU0Af2k16yZRuf/cMIPY3n0r XK41cehqZldoz+EzicIdSIEaXJr//184sJwD7ES4euh7HNw15jUF+7w3gtjI253p7Y7QWYu858Vq3 0dOzlAycnebIJB/vzWbG0pcCoMkKcNdbTEhMkE6iydjxtmLRsaRg4qDyYqwm3U0lBzR9rlFGUAH10 YjzaL2L0nLNA/txU2Io+Jd1Wosp7Wa83n0s9XAak00CoTHlzAuj6+p99MMPhWN4Mh18utGNQ/A0We tqylaKRLw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1htcNg-0006S8-2m; Fri, 02 Aug 2019 18:34:20 +0000 Date: Fri, 2 Aug 2019 11:34:19 -0700 From: Matthew Wilcox To: Chris Mason Cc: Dave Chinner , "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: <20190802183419.GC5597@bombadil.infradead.org> References: <20190801021752.4986-1-david@fromorbit.com> <20190801021752.4986-10-david@fromorbit.com> <20190801235849.GO7777@dread.disaster.area> <7093F5C3-53D2-4C49-9C0D-64B20C565D18@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7093F5C3-53D2-4C49-9C0D-64B20C565D18@fb.com> User-Agent: Mutt/1.11.4 (2019-03-13) 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 02:11:53PM +0000, Chris Mason wrote: > Yes and no. At some point important FS threads have the potential to > wait on every single REQ_META IO on the box, so every single REQ_META IO > has the potential to create priority inversions. [...] > Tejun reminded me that in a lot of ways, swap is user IO and it's > actually fine to have it prioritized at the same level as user IO. We > don't want to let a low prio app thrash the drive swapping things in and > out all the time, and it's actually fine to make them wait as long as > other higher priority processes aren't waiting for the memory. This > depends on the cgroup config, so wrt your current patches it probably > sounds crazy, but we have a lot of data around this from the fleet. swap is only user IO if we're doing the swapping in response to an allocation done on behalf of a user thread. If one of the above-mentioned important FS threads does a memory allocation which causes swapping, that priority needs to be inherited by the IO.