From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 A129E401A37; Mon, 29 Jun 2026 12:46:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782737170; cv=none; b=mfppTB2mU1FCi4UJ5V4ma2D7cZEeox5Lr4gcVoTwTQkuCQ5zgnvdeIHf+zk46xi64DL2lnp7YVYqp9l9cZd3N0fRRLDDrXB6CSRbudCyPKu1ZZvQKTZygFb7cQ35uigtqJM+BTjGWa1yBo447PtQsQmU4KL9MhOGlEg9rRnHizY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782737170; c=relaxed/simple; bh=389AEM2utSqn2fN8FAKtgkgAr4Z17AuWTFZfzIj2Gjk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kSgka/qaSHXIDERNeck18XPW3cB1U8OplBdPydPX8SUmfSEUSxK+TsMsE1gHsx38g+rpCpyDwvt1kEGVk+ohLRcM2Z3E+nfUfgnSjBjL5m31Uo98iBdVGEOeMUGYmKUSFOYCbqe0WMJjaH4ptM50H3lV+Y2TrjWmhqdYC2DtZXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 53E6668C7B; Mon, 29 Jun 2026 14:46:04 +0200 (CEST) Date: Mon, 29 Jun 2026 14:46:03 +0200 From: Christoph Hellwig To: Carlos Maiolino Cc: Jan Kara , Filip Blagojevic , Matthew Wilcox , Damien Le Moal , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: update BDI {io,ra}_pages values based on the RT device limits Message-ID: <20260629124603.GA23417@lst.de> References: <20260623142109.1838702-1-hch@lst.de> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <20260623142109.1838702-1-hch@lst.de> User-Agent: Mutt/1.5.17 (2007-11-01) So, I guess we're stuck with this approach? Or any other ideas? On Tue, Jun 23, 2026 at 04:21:05PM +0200, Christoph Hellwig wrote: > Hi all, > > we ran into a bit of a funny case where adding an SSD to store metadata > to a (zoned) XFS file system reduced the performance vs using a HDD for > both data and metadata. It turns out this is due to readahead code > looking at the BDI limits, including the io_pages value that can't be > inspected or tuned from userspace. > > This patch has the simplest fix for that by just updating the values from > XFS, but for a long-term solution this feels a bit ugly. Other, a lot > more invasive options would be: > > > 1) support multiple BDIs per file system. > > This would work pretty well for XFS, as data for a given file is > always entirely on one device, and the VFS writeback code is not > used for metadata. But it probably doesn't work well for other > cases > > 2) stop propagating these values through the BDI > > Have a way to query these parameters from the file system, either > through a method if we want to be fully dynamic, or through fields > instead of going through the BDI. The downside would be that > sysfs modifications of the readahead size would not work after > the file system initially queried them. > > Thoughts? ---end quoted text---