From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 58154848A; Wed, 31 Jan 2024 21:58:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706738308; cv=none; b=RREqfd1GgoszwjXYTObXfV3FyxQUi2w0oTvivnFvFKVArHCZcB4cE5TneuZYni5hTyF18lBHElydafH4+3WCdFB4/vQdwnJN+TFYNwVYxy/+rKxNjU3sXdfoYBI3QxIg0+F8zChwZcp6SKMsai7kSRnDTEIM41BkQq2GbKe5LPY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706738308; c=relaxed/simple; bh=OCJeKfhQ9glNLXX2ntf9uF6fRDRZS3kJloQ6WG9qz+0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Oss+OhbgcqQ1dcGfO9SCkNHAVb2Ex4DaXWA+5i4qzURSoURH9NufE/mfrO5cgfql+iid3GVVBp0lsazN6OPzDRZEpFOXqGx1MPnxSIH0bBlF2qiX0ebp8QzhrWE+UEfwU6REAzsLK0bMN/yX+f3yA8nu2+1+g6OXW5uWS5beEiQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=h5bIouCx; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="h5bIouCx" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=iQfXW37ZK31yG37Afle32aWwrDr+gCC0dupCwANd1vs=; b=h5bIouCxLjtlG+frdiQOFKm2uX U/2ZniW40PsD232UWulNNlEaoHXQ8vL020jg5yOCCTTa2+x+4cp4iN0RKjKmw/OFYhACLIHTwfHrr +OCXquWfqnT2hOYEFwKT6LLOUBLWA2LhvBYQNZ6mEUsnh/xuiGHLX8KHfraUJLSPSPCZ74ckbjL4L P5vpWzCdDLZG1+r+ZaXFv+NzQs/EblX49p6GNr5b3Ps9H8UMa0RrlxLERCzxFBPLMYC6RjWIx12M3 DUQzLrOfxDW43HkIUxSepWMBLAeXVqd6+SjoBG1E1Agz2p7Wd/eMuy2VQiUevb74HBKrZx5tEEB4E CXo+TkOA==; Received: from mcgrof by bombadil.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rVIbC-00000005dEB-100a; Wed, 31 Jan 2024 21:58:26 +0000 Date: Wed, 31 Jan 2024 13:58:26 -0800 From: Luis Chamberlain To: Matthew Wilcox Cc: kernel test robot , Daniel Gomez , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, "gost.dev@samsung.com" , Pankaj Raghav Subject: Re: [PATCH 1/2] test_xarray: add tests for advanced multi-index use Message-ID: References: <20231104005747.1389762-2-da.gomez@samsung.com> <202311152254.610174ff-oliver.sang@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Luis Chamberlain On Fri, Jan 26, 2024 at 08:32:28PM +0000, Matthew Wilcox wrote: > On Fri, Jan 26, 2024 at 12:04:44PM -0800, Luis Chamberlain wrote: > > > We have a perfectly good system for "relaxing": > > > > > > xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) { > > > xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE); > > > if (++tagged % XA_CHECK_SCHED) > > > continue; > > > > > > xas_pause(&xas); > > > xas_unlock_irq(&xas); > > > cond_resched(); > > > xas_lock_irq(&xas); > > > } > > > > And yet we can get a soft lockup with order 20 (1,048,576 entries), > > granted busy looping over 1 million entries is insane, but it seems it > > the existing code may not be enough to avoid the soft lockup. Also > > cond_resched() may be eventually removed [0]. > > what? you're in charge of when you sleep. you can do this: > > unsigned i = 0; > rcu_read_lock(); > xas_for_each(...) { > ... > if (iter++ % XA_CHECK_SCHED) > continue; > xas_pause(); > rcu_read_unlock(); > rcu_read_lock(); > } > rcu_read_unlock(); > > and that will get rid of the rcu warnings. right? The RCU warning was due to my getting an try call missing an RCU lock, I fixed that. The pending issue was a soft lockup that I get on low end systems testing test_xarray with higher order but after testing on a 2 vcpus with only 2 GiB of RAM I cannot reproduce so we can address this later. I forget the exact type of low end system I tested this on... but anyway I can't reproduce now. I suspect it may have been similar to the issue 0-day had found long ago and you noted an overloaded system [0] [0] https://lore.kernel.org/all/20190306120843.GI13380@bombadil.infradead.org/ Luis