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Christoph 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, Himanshu Madhani References: <20230929102726.2985188-1-john.g.garry@oracle.com> <20230929102726.2985188-2-john.g.garry@oracle.com> <20231109151013.GA32432@lst.de> <20231110062325.GB26516@lst.de> From: John Garry Organization: Oracle Corporation In-Reply-To: <20231110062325.GB26516@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO6P123CA0042.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:2fe::13) To DM6PR10MB4313.namprd10.prod.outlook.com (2603:10b6:5:212::20) Precedence: bulk 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IcBFhR2/YZwRdGAfCtsad3HzNO7HW6kyiWt/vpmAN3ofVYxCjCpKZy5OTDpPnpdfKSmDSIMmXOIp34kVEqvi+A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN0PR10MB5272 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=2023-11-10_05,2023-11-09_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 phishscore=0 suspectscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311060000 definitions=main-2311100075 X-Proofpoint-GUID: R5iOP_6LOtGC-a-fQdP7857J7b-TZ1dj X-Proofpoint-ORIG-GUID: R5iOP_6LOtGC-a-fQdP7857J7b-TZ1dj On 10/11/2023 06:23, Christoph Hellwig wrote: > On Thu, Nov 09, 2023 at 05:01:10PM +0000, John Garry wrote: >> Generally they come from the same device property. Then since >> atomic_write_unit_max_bytes must be a power-of-2 (and >> atomic_write_max_bytes may not be), they may be different. > How much do we care about supporting the additional slack over the > power of two version? I'm not sure yet. It depends on any merging support and splitting safeguards introduced. > >> In addition, >> atomic_write_unit_max_bytes is required to be limited by whatever is >> guaranteed to be able to fit in a bio. > The limit what fits into a bio is UINT_MAX, not sure that matters 😄 I am talking about what we guarantee that we can always fit in a bio according to request queue limits and bio vector count, e.g. if the request queue limits us to 8 segments only, then we can't guarantee to fit much in (without splitting) and need to limit atomic_write_unit_max accordingly. > >> atomic_write_max_bytes is really only relevant for merging writes. Maybe we >> should not even expose via sysfs. > Or we need to have a good separate discussion on even supporting any > merges. Willy chimed in that supporting merges was intentional, > but I'd really like to see numbers justifying it. > So far I have tested on an environment where the datarates are not high and any merging benefit was minimal to non-existent. But that is not to say it could help elsewhere. Thanks, John