From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 62BAC155398; Thu, 20 Mar 2025 14:31:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742481075; cv=none; b=kKtvhXsqyAaHwocM/8OWM+5lAzynGdKC9R6ufeYSQLgpWBPORFFeNFyID2b6JZgAKZir4uv6z3YHCrtYSqp7aFN32WP0UJ7W5wts6nnyUGgYOafbtgx1ufnFYX3tXI+nR+dd1tVeMZX5PFYUJHJ4Ev0K0T255TG2rhylBMLTmfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742481075; c=relaxed/simple; bh=FFSIXT5DcGX7/dkepbl74FSQUrt+QKc/N+V3dVJVCKk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UtfZyIq48HUfzrKB417Pfb9mLggIMUR0Hn6U2W/pXI5At5blcCAN+ipbt3H+87u5s1xaBWBrtbyzc/wW5U7aRVlLuAcfQroIKLPp0Kd1ztXkgI1tIQJTtq6iX1MtPlxJZ08/WydAyrzsZUjZTg4AUI0ssLH15qP4MSFl7xvAWyY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=hpptel6x; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.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="hpptel6x" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=NJZJ1FkgbSm88M1HAHaut+9UWjO501+rWTX6iMm1JYs=; b=hpptel6xf9qMXLORgmovdqNhsc x/1Qb0Kfq49q3b9UnlTmYq6W8erzzsDExlykz63TG9LKnT2bJXWX2L3kB5tywslbUyur3+MK9WfWe 3885xJ52ZM3P7Wspdlg0Mi/ahv5vBXr90doJLvQOONPhfQHVdpvxnh/x/rGn3NCJA2qfj2+KPWpGA wNQ812jt2LFC5N7+Sxb1KBZv5lJIVF9VAPsd/24oHrFoWAmIYrnNmBx8+9KscmD/NPbmftmbaAY8X M30c0nhdu9CxMt/7sAMeZqZ6zCuF55sx80DoF2xCtt2UAvoTB+gpIuNu5vnjLf+m703v1WCFwFE2c ek+FXj5Q==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tvGvL-0000000BzxE-2fcV; Thu, 20 Mar 2025 14:31:07 +0000 Date: Thu, 20 Mar 2025 14:31:07 +0000 From: Matthew Wilcox To: Daniel Gomez Cc: Luis Chamberlain , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, lsf-pc@lists.linux-foundation.org, david@fromorbit.com, leon@kernel.org, hch@lst.de, kbusch@kernel.org, sagi@grimberg.me, axboe@kernel.dk, joro@8bytes.org, brauner@kernel.org, hare@suse.de, djwong@kernel.org, john.g.garry@oracle.com, ritesh.list@gmail.com, p.raghav@samsung.com, gost.dev@samsung.com, da.gomez@samsung.com Subject: Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64 Message-ID: References: Precedence: bulk X-Mailing-List: linux-block@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: On Thu, Mar 20, 2025 at 02:29:56PM +0100, Daniel Gomez wrote: > On Thu, Mar 20, 2025 at 12:11:47PM +0100, Matthew Wilcox wrote: > > On Thu, Mar 20, 2025 at 04:41:11AM -0700, Luis Chamberlain wrote: > > > We've been constrained to a max single 512 KiB IO for a while now on x86_64. > > ... > > > It does beg a few questions: > > > > > > - How are we computing the new max single IO anyway? Are we really > > > bounded only by what devices support? > > > - Do we believe this is the step in the right direction? > > > - Is 2 MiB a sensible max block sector size limit for the next few years? > > > - What other considerations should we have? > > > - Do we want something more deterministic for large folios for direct IO? > > > > Is the 512KiB limit one that real programs actually hit? Would we > > see any benefit from increasing it? A high end NVMe device has a > > bandwidth limit around 10GB/s, so that's reached around 20k IOPS, > > which is almost laughably low. > > Current devices do more than that. A quick search gives me 14GB/s and 2.5M IOPS > for gen5 devices: > > https://semiconductor.samsung.com/ssd/enterprise-ssd/pm1743/ > > An gen6 goes even further. That kind of misses my point. You don't need to exceed 512KiB I/Os to be bandwidth limited. So what's the ROI of all this work? Who benefits?