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 X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26FCEC31E40 for ; Sat, 3 Aug 2019 15:53:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED4662085B for ; Sat, 3 Aug 2019 15:53:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564847638; bh=KLBnMj3Tyuap/WV7l+1iISEe2D3I5txGEIYh/f4Aea0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=RIn3q7YcvbN41VVsCs9mdH80YTiTnS7efJXgTBiYBhtjPamzSoe1Um37a8uNoa/4+ gPdDw7FRhXJsTdhsFm7jWbmzqCY71tkeqwaNUrC4sVWN403+7T4EtiSToloKT8oc6y KfpRx2ctaLbshNXGA5WWxwvFuKjQaNZF1UN0J6tM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728043AbfHCPxx (ORCPT ); Sat, 3 Aug 2019 11:53:53 -0400 Received: from mail-qk1-f195.google.com ([209.85.222.195]:39692 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727758AbfHCPxw (ORCPT ); Sat, 3 Aug 2019 11:53:52 -0400 Received: by mail-qk1-f195.google.com with SMTP id w190so57147119qkc.6; Sat, 03 Aug 2019 08:53:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=wr1/jf7OC4N1CyD2pZrJRAsqKQhTrW81tkA/dMeoZYU=; b=E4xysODT5QEs0YiJh/6lyT4EBx4B7Mz7IMg6xczGcQ0G9Qk2AtE4TXZ+GCBgFJDEi1 lLnFymeOoSvdAYvHJIdCSSrgbeDE4a17sW8u6K0mHvhTIQr7wv8IU/Sst4zTTu0Ui9p9 jfnV5m2JmluBR+fiHIHyCypa6MemIx71M5jmKx6vtYPIEIc/gtcjHdvjaf5qkicR216B vr2TNHeSv9J9+fUNK7YQ/gOyrhWAGf5rfXuyH6O/uIOIbbVZkbs1h8vugk98ksEkGk+E kSQOd/o+FqbgLWKvjIyIdPT1Sa9ivX+Vce/lqYQCUaRKFWaUnKiHZKnPlvGognn7X6L+ Xw7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=wr1/jf7OC4N1CyD2pZrJRAsqKQhTrW81tkA/dMeoZYU=; b=oAJMdL6UK+ZddtmyZsbBLrWBufvasDrn6uavDuGaXa3KqooltNNmYgG7mQV1wOAd+d Om6SROdQquOIEHnj59eUzikbbKbdQwWvg7ZFg6rsaENPNlqBs0kTUTJJn1+VamfXaxUF w7MuS8SItSyXsSkctXqfHeEZAFEUQj3wU+z0jcXv9CSKUYa7QS64FXgf1x7XUNuNpMdf wIvJJApFBBpmF1jnpLThM2wYtvB0HQVd90DwJ5UKu8R8+5hRjRlsAtq2/nFRV0+TfH59 dhBCZFiIKvB6EjFUYdKf9+2mif1MI+nVCEmxPv9OJUEqoQdI5PA9NYsoMLvRDGripmzO a8xg== X-Gm-Message-State: APjAAAWINjFwzOL3mWwM3owRzVmqMTOK9/JO4oeICzuDuwPPctQL2lLX ZpWWFjjnAYsGA2aZKc5Iqt8= X-Google-Smtp-Source: APXvYqxgFYSi0U8M7Pxq58YMG2KJi0fk/qfGLpdfgkpRW+ewtu0h1e0nP4F1pryg35uOv1I+y7chQA== X-Received: by 2002:a37:6085:: with SMTP id u127mr96259447qkb.25.1564847631510; Sat, 03 Aug 2019 08:53:51 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::7cfa]) by smtp.gmail.com with ESMTPSA id r205sm38568262qke.115.2019.08.03.08.53.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 03 Aug 2019 08:53:50 -0700 (PDT) Date: Sat, 3 Aug 2019 08:53:49 -0700 From: Tejun Heo To: Matthew Wilcox 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: <20190803155349.GD136335@devbig004.ftw2.facebook.com> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-3-tj@kernel.org> <20190803153908.GA932@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190803153908.GA932@bombadil.infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. Thanks. -- tejun