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Hellwig Cc: axboe@kernel.dk, kbusch@kernel.org, sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, chandan.babu@oracle.com, dchinner@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com, linux-api@vger.kernel.org References: <20230929102726.2985188-1-john.g.garry@oracle.com> <20230929102726.2985188-3-john.g.garry@oracle.com> <20231109151343.GB32432@lst.de> From: John Garry Organization: Oracle Corporation In-Reply-To: <20231109151343.GB32432@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO2P265CA0325.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a4::25) To DM6PR10MB4313.namprd10.prod.outlook.com (2603:10b6:5:212::20) Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: 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a71yk/+rJYXsTBTFUlo/K++QdSsMGAn2ZavsT0YF2+Hg3BYFdSA4011VtI8VEKIsf3e+fKOWLAdqvxXQERZBHw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM3PR10MB7948 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-09_14,2023-11-09_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 malwarescore=0 suspectscore=0 adultscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311060000 definitions=main-2311090133 X-Proofpoint-ORIG-GUID: lDk2RUBgL_UOXwuEccS2ojle-2Acl_Wc X-Proofpoint-GUID: lDk2RUBgL_UOXwuEccS2ojle-2Acl_Wc On 09/11/2023 15:13, Christoph Hellwig wrote: > On Fri, Sep 29, 2023 at 10:27:07AM +0000, John Garry wrote: >> We rely the block layer always being able to send a bio of size >> atomic_write_unit_max without being required to split it due to request >> queue or other bio limits. >> >> A bio may contain min(BIO_MAX_VECS, limits->max_segments) vectors, >> and each vector is at worst case the device logical block size from >> direct IO alignment requirement. > A bio can have more than BIO_MAX_VECS if you use bio_init. Right, FWIW we are only concerned with codepaths which use BIO_MAX_VECS, but I suppose that is not good enough as a guarantee. > >> +static unsigned int blk_queue_max_guaranteed_bio_size_sectors( >> + struct request_queue *q) >> +{ >> + struct queue_limits *limits = &q->limits; >> + unsigned int max_segments = min_t(unsigned int, BIO_MAX_VECS, >> + limits->max_segments); >> + /* Limit according to dev sector size as we only support direct-io */ > Who is "we", and how tells the caller to only ever use direct I/O? I think that this can be dropped as a comment. My earlier series used PAGE_SIZE and not sector size here, which I think was proper. > And how would a type of userspace I/O even matter for low-level > block code. It shouldn't do, but we still need to limit according to request queue limits. > What if I wanted to use this for file system metadata? > As mentioned, I think that the direct-IO comment can be dropped. Thanks, John