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[198.145.29.99]) by mx.google.com with ESMTPS id x20si8927727plm.61.2019.08.06.16.01.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Aug 2019 16:01:04 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=ram+yxpj; spf=pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8C7A32070D; Tue, 6 Aug 2019 23:01:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565132464; bh=vGl/qyUj+m3xdNJaJ9fF/HjSzIEZvTJK5xJjIUiHOxQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ram+yxpjoZZlMPdi2p/p8wC9xbLXU244ul4IK2w7JME7Dob0R4Qy/D1hsmAvZ0GDM lPuIhCuLFw5/g2cagStWN5Eua65k6HVxgrIAfPon7hrUHTVSJGBaJH22M3WDg17C6L TdVf/pEW1LNxxYciU9FWLJmB9xyejRP00N6oKK4k= Date: Tue, 6 Aug 2019 16:01:02 -0700 From: Andrew Morton To: Tejun Heo Cc: axboe@kernel.dk, jack@suse.cz, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, guro@fb.com Subject: Re: [PATCH 2/4] bdi: Add bdi->id Message-Id: <20190806160102.11366694af6b56d9c4ca6ea3@linux-foundation.org> In-Reply-To: <20190803140155.181190-3-tj@kernel.org> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-3-tj@kernel.org> 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-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 Sat, 3 Aug 2019 07:01:53 -0700 Tejun Heo wrote: > There currently is no way to universally identify and lookup a bdi > without holding a reference and pointer to it. This patch adds an > non-recycling bdi->id and implements bdi_get_by_id() which looks up > bdis by their ids. This will be used by memcg foreign inode flushing. Why is the id non-recycling? Presumably to address some lifetime/lookup issues, but what are they? Why was the IDR code not used? > I left bdi_list alone for simplicity and because while rb_tree does > support rcu assignment it doesn't seem to guarantee lossless walk when > walk is racing aginst tree rebalance operations. > > ... > > +/** > + * bdi_get_by_id - lookup and get bdi from its id > + * @id: bdi id to lookup > + * > + * Find bdi matching @id and get it. Returns NULL if the matching bdi > + * doesn't exist or is already unregistered. > + */ > +struct backing_dev_info *bdi_get_by_id(u64 id) > +{ > + struct backing_dev_info *bdi = NULL; > + struct rb_node **p; > + > + spin_lock_irq(&bdi_lock); Why irq-safe? Everywhere else uses spin_lock_bh(&bdi_lock). > + p = bdi_lookup_rb_node(id, NULL); > + if (*p) { > + bdi = rb_entry(*p, struct backing_dev_info, rb_node); > + bdi_get(bdi); > + } > + spin_unlock_irq(&bdi_lock); > + > + return bdi; > +} > + > > ... >