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 18D0B3515D5; Wed, 19 Aug 2026 07:21:42 +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=1787124104; cv=none; b=jNDolCX8/8aFWRQsLJWD2nRunUkq+iNcKd2k52y8wUsHbTLUkTRyNlhBn7SYSxVc8SZSTxhj3VNOMB5LEokHuL7O3IunNpuV/KcZmrnxhQkvaw/pVPxNmraW2qpHINU4VwV0EOD760SqN1+hGWoAFGngClmCiVAAmOFvDVHOeFI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787124104; c=relaxed/simple; bh=JLmWBd13CdMp0qtnOUeYYS5wJYaVdUn3H3Oy1zORrPc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Qk2GDSCeJEWSOedzc3tIvPvNihVzuc76GNfHE+zq/tMcL1g+k76eLfRLiTQsix14fjD8RlkSkxImQPZgOWpPh1ileuFDEYS1XoS51A8dGrCU4KeEZ/a4X87fkkdv8SbS6iRqjgCdQc/U4+00t7fBfECAZNMqJIo3iQmEQet1VW8= 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 90B4C68C7B; Wed, 19 Aug 2026 09:21:37 +0200 (CEST) Date: Wed, 19 Aug 2026 09:21:37 +0200 From: Christoph Hellwig To: Kanchan Joshi Cc: brauner@kernel.org, hch@lst.de, djwong@kernel.org, dgc@kernel.org, jack@suse.cz, cem@kernel.org, axboe@kernel.dk, kbusch@kernel.org, ritesh.list@gmail.com, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, gost.dev@samsung.com, Anuj Gupta Subject: Re: [PATCH v4 4/6] xfs: generic AG set based steering Message-ID: <20260819072137.GG1541@lst.de> References: <20260717125538.508925-1-joshi.k@samsung.com> <20260717125538.508925-5-joshi.k@samsung.com> 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: <20260717125538.508925-5-joshi.k@samsung.com> User-Agent: Mutt/1.5.17 (2007-11-01) On Fri, Jul 17, 2026 at 06:25:36PM +0530, Kanchan Joshi wrote: > Improve allocator concurrency and reduce interleaving by introducing > fixed sized AG set. > Use low bits of the inode as a hash to select AG within the AG set. > Overall, a file will try to use the same AG (and contiguity is maintained), > but multiple files will be spread across all AGs in the target AG set. I'm a bit worried this kind of magic - the inodes close to each other might not all have data or very different amounts of data. I suspect the root cause this helps with is that the XFS initial data placement algorithm that tries to place file data next to the inode is actively harmful these days. So doing an initial AG selection similar to how the RT device does the initial RTG selection might be more useful here (and thinking about moving to an inode32-like scheme where small metadata with a lot of churn is constrained to a few AGs).