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Thu, 3 May 2018 17:20:32 -0400 Received: from mail-pg0-f43.google.com ([74.125.83.43]:38803 "EHLO mail-pg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751261AbeECVUa (ORCPT ); Thu, 3 May 2018 17:20:30 -0400 X-Google-Smtp-Source: AB8JxZo/sZ/VdXQKFlcEDCOqouyGijqCKgTSwauBN/eOThn7cxiSmx428G16jBVSDrvUcI0huHWddA== Subject: Re: [PATCH v2] fs: Add aio iopriority support for block_dev To: Adam Manzanares , Matthew Wilcox Cc: "viro@zeniv.linux.org.uk" , "bcrl@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "linux-api@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20180503182114.2797-1-adam.manzanares@wdc.com> <20180503183353.GC1562@bombadil.infradead.org> <47e0a519-37b4-f5e7-0616-8659d11c2b69@wdc.com> <18300bdb-a12f-0b6c-1317-6db3e4391d57@kernel.dk> From: Jens Axboe Message-ID: <9e3ba3eb-9c41-3b5d-dc12-f9ef573ab53f@kernel.dk> Date: Thu, 3 May 2018 15:20:26 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 5/3/18 2:58 PM, Adam Manzanares wrote: > > > On 5/3/18 1:24 PM, Jens Axboe wrote: >> On 5/3/18 2:15 PM, Adam Manzanares wrote: >>> >>> >>> On 5/3/18 11:33 AM, Matthew Wilcox wrote: >>>> On Thu, May 03, 2018 at 11:21:14AM -0700, adam.manzanares@wdc.com wrote: >>>>> If we want to avoid bloating struct kiocb, I suggest we turn the private field >>>>> into a union of the private and ki_ioprio field. It seems like the users of >>>>> the private field all use it at a point where we can yank the priority from >>>>> the kiocb before the private field is used. Comments and suggestions welcome. >>>> >>>> Or we could just make ki_hint a u8 or u16 ... seems unlikely we'll need >>>> 32 bits of ki_hint. (currently defined values are 1-5) >>> >>> I like the approach of using a u16 for the ki_hint. I'll update and >>> resubmit. >> >> It's intended to be a mask. If you do shrink it for now, then we need some >> guard code to ensure it can always carry what it needs to. >> > > Got it, I'll add the guard to rw_hint_valid along with a comment about > being limited by the size of ki_hint in case we get to a situation where > 16 bits is not enough. Other way around - the API should not be limited by the fact that some smaller type was chosen for an internal structure. Hence the guard/check should not be in rw_hint_valid, but rather around where you assign ki_hint. If/when we do extend the read/write hints, then we'll potentially need to bump ki_hint to accommodate it. -- Jens Axboe