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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id 78si39946109pfz.268.2019.08.03.09.17.48 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sat, 03 Aug 2019 09:17:48 -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=YTMLQb4x; 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=/X3WDI0mWhLkrrAZYpOBF14jsWJC/LWwN2nM68m2FXE=; b=YTMLQb4x9LXJC64dxUjr6v4Xk GMXQsTaDR1vmYROgRuPGQmcgEYe76/aACMQQWCtkZimsYaMoot1ZvwPQDm2Ihc2qq7OidsOSLkgi5 5h4VKxOmA9p2bsT/wyW0eiE02ATnGIGZFQZ1DcJKqPFLLhndN++tne2fJkGXmLxkZ5sdM7ADQfEHj ZUnzIYOL2jqDrOkrkXILUmtHBpDlM7HqH5QWkJ6gkEmQSJSg1PFxAP5KxYT78scR0A+zv9wLYi74s ucUhUJiJLtSFE9BZiIREAP1CItRqGkb5o5/6a4VXeKUPosSTon4rRzJYDNgxMmGjhEAcUMcDZEnKr HD/miYdsw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1htwj1-0007V1-Ge; Sat, 03 Aug 2019 16:17:43 +0000 Date: Sat, 3 Aug 2019 09:17:43 -0700 From: Matthew Wilcox 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, akpm@linux-foundation.org Subject: Re: [PATCH 2/4] bdi: Add bdi->id Message-ID: <20190803161743.GB932@bombadil.infradead.org> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-3-tj@kernel.org> <20190803153908.GA932@bombadil.infradead.org> <20190803155349.GD136335@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190803155349.GD136335@devbig004.ftw2.facebook.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 Sat, Aug 03, 2019 at 08:53:49AM -0700, Tejun Heo wrote: > Hey, Matthew. > > On Sat, Aug 03, 2019 at 08:39:08AM -0700, Matthew Wilcox wrote: > > On Sat, Aug 03, 2019 at 07:01:53AM -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. > > > > > > 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. > > > > This would seem like the perfect use for an allocating xarray. That > > does guarantee lossless walk under the RCU lock. You could get rid of the > > bdi_list too. > > It definitely came to mind but there's a bunch of downsides to > recycling IDs or using radix tree for non-compacting allocations. Ah, I wasn't sure what would happen if you recycled an ID. I agree, the radix tree is pretty horrid for monotonically increasing IDs. I'm still working on the maple tree to replace it, but that's going slower than I would like, so I can't in good conscience ask you to wait for it to be ready.