From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:57585 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388390AbgLCIaf (ORCPT ); Thu, 3 Dec 2020 03:30:35 -0500 Date: Thu, 3 Dec 2020 09:29:51 +0100 From: Christoph Hellwig Subject: Re: [PATCH 3/9] block: store a block_device pointer in struct bio Message-ID: <20201203082951.GA15581@lst.de> References: <20201201165424.2030647-1-hch@lst.de> <20201201165424.2030647-4-hch@lst.de> <20201203063941.GA629758@T590> <20201203071055.GA633702@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201203071055.GA633702@T590> List-ID: To: Ming Lei Cc: Christoph Hellwig , Jens Axboe , Tejun Heo , Coly Li , Song Liu , dm-devel@redhat.com, linux-bcache@vger.kernel.org, linux-raid@vger.kernel.org, linux-s390@vger.kernel.org, linux-block@vger.kernel.org On Thu, Dec 03, 2020 at 03:10:55PM +0800, Ming Lei wrote: > On Thu, Dec 03, 2020 at 02:40:04PM +0800, Ming Lei wrote: > > On Tue, Dec 01, 2020 at 05:54:18PM +0100, Christoph Hellwig wrote: > > > Replace the gendisk pointer in struct bio with a pointer to the newly > > > improved struct block device. From that the gendisk can be trivially > > > accessed with an extra indirection, but it also allows to directly > > > look up all information related to partition remapping. > > > > The extra indirection is often done in fast path, so just wondering why > > you don't consider to embed gendisk into block_device? Then the extra > > indirection can be avoided. > > oops, that is only possible for disk, and indirection is still needed > for partitions. I looked into that, but given that the block device is allocated as part of the inode we'd need to tell ->alloc_inode if we want to allocate the small inode without the gendisk, or the large one with it which doesn't work with the current interface. Beause the hd_struct is gone we're still not using more structures in the I/O path than we did before.