From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:38791 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727105AbeJRXXF (ORCPT ); Thu, 18 Oct 2018 19:23:05 -0400 Date: Thu, 18 Oct 2018 17:21:33 +0200 From: Christoph Hellwig To: Matthew Wilcox Cc: Christoph Hellwig , Ming Lei , Jens Axboe , linux-block@vger.kernel.org, Vitaly Kuznetsov , Dave Chinner , Linux FS Devel , "Darrick J . Wong" , xfs@vger.kernel.org, Bart Van Assche Subject: Re: [PATCH 0/5] block: introduce helpers for allocating io buffer from slab Message-ID: <20181018152133.GA28300@lst.de> References: <20181018131817.11813-1-ming.lei@redhat.com> <20181018140342.GB32429@bombadil.infradead.org> <20181018140551.GA26500@lst.de> <20181018150605.GC32429@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181018150605.GC32429@bombadil.infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, Oct 18, 2018 at 08:06:05AM -0700, Matthew Wilcox wrote: > Can you name one that does require 512-byte alignment, preferably still > in use? Or even >4-byte alignment. I just checked AHCI and that requires > only 2-byte alignment. Xen-blkfront, rsxx, various SD/MMC card readers for example. > I have reason to believe that these are uncommon because of the feedback > we got in the NVMe committee after releasing 1.0 which required 4-byte > alignment from people whining that they just couldn't guarantee 4-byte > alignment in their host devices and they absolutely needed to have no > alignment requirements (!) See how things turned - after NVMe SGLs followed the no alignment rule enough controller vendors rebelled so that NVMe 1.3 has an option of SGL support only if 4-byte aligned.